Blackhead disease (histomoniasis) in poultry: a critical review

18S rRNA gene metabarcoding for investigation of gastrointestinal parasite diversity in great cormorants

The great cormorant (Phalacrocorax carbo) is a migratory, fish-eating bird that may act as a carrier for various pathogens, raising potential ecological and public health concerns. This study investigated the diversity of gastrointestinal parasites in great cormorants from the Republic of Korea using 18S rRNA gene metabarcoding and conventional diagnostic methods. Fecal samples were collected from 10 great cormorants in Korea, and DNA was extracted for metabarcoding targeting the V4 and V9 regions of the 18S rRNA gene using the MiSeq platform. Conventional PCR and microscopic examination were used for validation. The V4 region of the 18S rRNA gene revealed the presence of Baruscapillaria spiculata, Contracaecum sp., and Isospora lugensae. The V9 region analysis identified the following parasites: Tetratrichomonas sp., Histomonas meleagridis, Trichomitus sp., Tetratrichomonas prowazekii, B. obsignata, Monosiga ovata, and Fasciola gigantica. Furthermore, conventional PCR confirmed the presence of Contracaecum sp., Isospora sp., and unspecified trichomonads, and microscopic examination identified eggs of capillarid, Contracaecum, and Eustrongylides and trophozoites of flagellated protozoa in the collected cormorant fecal samples. The findings underscored the potential ecological role of great cormorants as hosts for diverse gastrointestinal parasites and the utility of 18S rRNA gene metabarcoding for screening the diversity of gastrointestinal parasites in great cormorants.

Inhibitory effects of different plant extracts on Histomonas meleagridis in vitro and in vivo in chickens

Histomonosis is a protozoan disease that is caused by Histomonas meleagridis, which can lead to cecal inflammation and liver necrosis in poultry. Since the discontinuation of nitarsone in 2015, there is currently a lack of approved prophylactics for managing histomonosis. In search of potential alternatives, the present investigation evaluated the inhibitory effects of seven commercial plant extracts on the in vitro growth of H. meleagridis. Additionally, the in vivo effectiveness of three of the most promising plant extracts was evaluated. The study demonstrated that all seven plant extracts exhibited antihistomonal properties in vitro. Sodium houttuyfonate, emodin, and osthole displayed the highest effectiveness among these extracts, as evidenced by their respective minimal lethal concentration of 0.25, 0.5, and 1 mg/mL. Subsequently, these three plant extracts were employed in additional in vivo testing. The results indicated that all three extracts could mitigate liver and cecum lesion scores in infected chickens while facilitating a degree of body weight gain following infection compared to the challenged control. The group administered with 0.5 g/kg (feed) sodium houttuyfonate exhibited the most pronounced effect, as evidenced by the absence of a significant difference in weight gain compared to the dimetridazole group (P < 0.05). However, the three plant extracts did not fully restore the body weight of infected chickens to levels comparable with the blank control. The experimental results indicate that sodium houttuyfonate, emodin, and osthole possess properties that contribute to the prevention and treatment of histomonosis, with sodium houttuyfonate demonstrating the most favorable results.

Biosecurity Implications, Transmission Routes and Modes of Economically Important Diseases in Domestic Fowl and Turkey

The poultry industry is a critical source of affordable protein worldwide; however, it faces continuous threats from various poultry diseases that significantly impact public health, economic stability, and food security. Knowledge of and examination of the transmission routes, risk factors, and environmental survival characteristics of the most important pathogens affecting poultry populations, as well as the importance of strict biosecurity, are pivotal. Transmission routes are split into direct and vector-borne pathways, and indirect ways, which include infections via contaminated surfaces and vector-borne pathways, including insects and rodents. Avian influenza virus and Newcastle disease virus spread through respiratory droplets, and their transmission risk increases with increasing stocking density. While other pathogens (e.g., infectious bursal disease virus and Salmonella spp.), to persist long-term in the environments, for example, feed and litter, increasing the probability to persist long-term in the environments, for example, feed and litter, increasing the probability of infection. The long-term resilience of pathogens in multiple pathogens in various environmental conditions highlights the role of biosecurity, sanitation, and hygiene controls in preventing disease outbreaks. High stocking density in production systems, suboptimal ventilation, and inadequate biosecurity controls further increase transmission risks. This paper summarizes important disease transmissions and reinforces the need for strict biosecurity protocols and routine health monitoring to prevent the spread of pathogens within and beyond poultry facilities. These strategies can support safe poultry production, address growing global demand, and ensure food safety and public health.

Host-specific targets of Histomonas meleagridis antigens revealed by immunoprecipitation

Histomonas meleagridis, a protozoan parasite responsible for histomonosis (syn. Blackhead disease, histomoniasis), presents an increasing challenge for poultry health, particularly with the ban of licensed prophylactic and treatment options. Recent studies have explored H. meleagridis proteome, exoproteome, and surfaceome, linking molecular data to virulence and in vitro attenuation. Nevertheless, proteins involved in interactions with hosts remain largely unknown. In this study, we conducted immunoproteome analyses to identify key antigens involved in the humoral immune response of the parasite's main hosts, turkeys and chickens. Immunogenic proteins were isolated via immunoprecipitation using sera from chickens and turkeys that were vaccinated with a single attenuated strain and challenged with virulent strains of the protozoan, respectively. Mass spectrometry identified 155 putative H. meleagridis immunogenic proteins, of which 43 were recognized by sera from both hosts. In silico antigenicity screening (VaxElan) identified 33 pan-reactive antigens, with VaxiDL further highlighting 10 as potential vaccine candidates. Comparative analysis revealed host-specific immune responses, with 16 differential immunogenic proteins in chickens (6 specific to virulent and 10 to attenuated preparations) and 19 unique proteins in turkeys, all associated with virulent strains. These results enhance our understanding of H. meleagridis immunogenic protein dynamics and host-pathogen specificities, supporting the development of improved diagnostic tools and potential protective measures against the infection.

Evaluation of an attenuated chicken-origin Histomonas meleagridis vaccine for the prevention of histomonosis in chickens

Introduction

Histomonosis, a protozoan disease caused by Histomonas meleagridis, poses a significant economic burden on domestic poultry in China. To reduce the losses caused by this disease in chickens, an attenuated vaccine was developed by exploiting the diminished virulence of H. meleagridis through successive in vitro passages.

Methods

Four experiments were conducted to evaluate the viability of attenuated H. meleagridis as a potential vaccine candidate. Experiment 1 evaluated the route of infection (oral vs. intracloacal) and dose (5 × 104, 1 × 105, and 2 × 105 H. meleagridis/chicken) using the virulent strain H. meleagridis JSYZ-D10. Experiment 2 evaluated the attenuated effect of the H. meleagridis JSYZ-D168 strain (infection dose: 2 × 105 H. meleagridis/chicken). Experiment 3 evaluated the immunoprotective effect of different immunization doses (5 × 104, 1 × 105, and 2 × 105 H. meleagridis/chicken). Experiment 4 evaluated the immunoprotective effect of different immunization schedules (immunization at 3 days of age; immunization at 14 days of age; two immunizations, one at 3 days of age and one at 14 days of age; immunization and infection dose: 2 × 105 H. meleagridis/chicken).

Results

The results showed that the intracloacal route of infection was more effective and stable compared to the oral route. The pathogenicity of the JSYZ-D168 H. meleagridis strain was significantly reduced compared to the original virulent strain. Chickens vaccinated by intracloacal immunization at a dose of 2 × 105 H. meleagridis/chicken on day 14 provided effective protection against a virulent strain challenge, significantly resulting in increased body weight and reduced lesions in the cecum and liver within 28 days post-immunization (p < 0.05). Poor immunoprotection was obtained either when the immunization dose was 1 × 105 H. meleagridis/chicken or when the immunization program was a single immunization at 3 days of age only.

Discussion

In conclusion, the administration of a vaccine provides a measurable degree of protection against the detrimental effects induced by H. meleagridis, thus warranting its endorsement in clinical settings.

Metabolic Profile of Histomonas meleagridis in Dwyer's Media with and Without Rice Starch

BACKGROUND AND OBJECTIVES

Histomonas meleagridis, the causative agent of histomonosis (i.e., blackhead disease), threatens the poultry industry with serious economic losses due to its high mortality and morbidity in turkey and chicken flocks. In vitro studies are complicated by the inability to culture the parasite axenically. Histomonas meleagridis has been propagated in Dwyer's media, which contains a starch source and serum, for over 50 years. The presence of insoluble starch component in Dwyer's media represents an obstacle for the commercialization of such media, and the role of starch in media is poorly understood.

METHODS

To investigate the intracellular metabolomic differences in H. meleagridis and undefined bacteria grown in Dwyer's media with rice starch (SD) and without rice starch (NR), we conducted a global metabolomics analysis using ultra-high-performance liquid chromatography-high-resolution mass spectrometry.

RESULTS

SD significantly supported the growth of H. meleagridis compared to NR. There was no significant difference in bacterial growth between SD and NR media at various timepoints. From the intracellular metabolic analysis of samples collected from the SD and NR media, a total of 170 known metabolites were identified. H. meleagridis appears to be the major contributor to global metabolic differences.

CONCLUSIONS

We found that riboflavin had the highest variable importance in the projection score, and metabolites involved in riboflavin biosynthesis significantly contributed to the differences between SD and NR in the media immediately after the inoculation of H. meleagridis and undefined bacteria, warranting further investigations into the role of riboflavin biosynthesis in H. meleagridis growth.

Hepatic transcriptomic analysis reveals differential regulation of metabolic and immune pathways in three strains of chickens with distinct growth rates exposed to mixed parasite infections

During parasite infections, the liver may prioritise immune-related pathways over its metabolic functions. Intestinal infections caused by Ascaridia galli and Heterakis gallinarum impair feed intake, nutrient absorption, and weight gain. Histomonas meleagridis, vectored by H. gallinarum, can also damage liver tissues, potentially impairing liver functions. This study examined the hepatic gene expression in three strains of chickens: Ross-308 (R), Lohmann Brown Plus (LB), and Lohmann Dual (LD), 2 weeks after an experimental infection (n = 18) with both A. galli and H. gallinarum or kept as uninfected control (n = 12). Furthermore, H. gallinarum infection led to a co-infection with H. meleagridis. The mixed infections reduced feed intake and the average daily weight gain (P < 0.001). The infections also increased the plasma concentrations of alpha (1)-acid glycoprotein and the antibody titre against H. meleagridis (P = 0.049), with no strain differences (P > 0.05). For host molecular response, 1887 genes were differentially expressed in LD, while 275 and 25 genes were differentially expressed in R and LB, respectively. The up-regulated genes in R and LD were mostly related to inflammatory and adaptive immune responses, while down-regulated genes in LD were involved in metabolic pathways, including gluconeogenesis. Despite performance differences among the strains, worm burdens were similar, but hepatic molecular responses differed significantly. Moreover, there was an indication of a shift in hepatic functions towards immune-related pathways. We, therefore, conclude that the liver shifts its functions from metabolic to immune-related activities in chickens when challenged with mixed parasite species.

Diversity of gastrointestinal parasites of turkeys (Meleagris gallopavo) under different housing systems in Bessarabia, Ukraine

The development of turkey farming is significantly restrained by parasitic diseases, which have become widespread and cause significant economic losses to specialized- and homestead farms. This study aimed to determine the prevalence of endoparasites in turkeys of different age groups under different maintenance systems and the nature of patho-anatomical changes depending on the course of the disease. A total of 1,869 samples of fecal from turkeys were studied. From turkeys kept in poultry houses, 925 fecal samples and 944 fecal samples from free-range turkeys were examined. In turkeys that were kept in a poultry house, the total infection with endoparasites was 59.8 %, while in free range, it was 63.3 %. The most common in turkeys 30-60 days old from poultry houses are Histomonas meleagridis (21.5 %), Eimeria spp. (11.5 %) and Cryptosporidium baileyi (15.5 %) and in free-range turkeys - Histomonas meleagridis (15.6 %), Eimeria spp. (7.2 %) and Cryptosporidium baileyi (10.8 %). Cryptosporidium baileyi was not observed in turkeys 360 days old or older. Tetratrichomonas gallinarum was most frequently recorded in turkeys 90 - 120 days old from poultry houses (3.8 %) and turkeys 150 - 180 days old in free range (3.7 %). Ascaridia dissimilis is most common in free-range turkeys 90 - 120 days old (11.8 %) and turkeys 150 - 180 days old from poultry houses (9.5 %). Heterakis gallinarum was primarily recorded in turkeys 150 - 180 days old under both systems of keeping with a value range from 16.2 to 17.2 %. Infestation of 150 - 180-day-old free-range turkeys by cestodes Davainea meleagridis and Raillietina echinobothrida was 15.0 % and 12.9 %, respectively. Thus, the diversity and prevalence of gastrointestinal tract invasions depend on the age and housing system of the poultry.

HISTOMONAS MELEAGRIDIS INFECTIONS IN TURKEYS IN THE USA: A CENTURY OF PROGRESS, RESURGENCE, AND TRIBUTE TO ITS EARLY INVESTIGATORS, THEOBALD SMITH, ERNST TYZZER, AND EVERETT LUND

Histomoniasis, caused by the protozoan, Histomonas meleagridis, is an economically important disease of turkeys, and it also affects several other species of domesticated and wild Galliformes, including chickens. Under natural conditions, the parasite is transmitted through eggs of a nematode, Heterakis gallinarum, that shares its hosts with Hi. meleagridis. The protozoan infects tissues of both male and female He. gallinarum and eventually is carried within the worm egg. Histomonas meleagridis more readily infects and develops in chickens, and the proximity of chicken farms is a major risk factor for outbreaks in turkeys. Chemoprophylaxis had controlled Hi. meleagridis in turkeys very successfully, but histomoniasis has recently reemerged in turkeys because anti-histomonal drugs are no longer permitted by the United States Food and Drug Administration because of the concerns for residual toxins in poultry meat. Horizontal transmission of the protozoan in the absence of worm eggs remains a mystery because the flagellate trophozoite excreted in the feces of turkeys is not viable for any length of time. A proposed resistant stage of the protozoan has not yet been conclusively demonstrated. Here we review the discovery of the protozoan and the current status of the disease and its control.

MicroRNA expression profile of chicken liver at different times after Histomonas meleagridis infection

Histomonas meleagridis, an anaerobic intercellular parasite, is known to infect gallinaceous birds, particularly turkeys and chickens. The resurgence of histomonosis in recent times has resulted in significant financial setbacks due to the prohibition of drugs used for disease treatment. Currently, research on about H. meleagridis primarily concentrate on the examination of its virulence, gene expression analysis, and the innate immunity response of the host organism. However, there is a lack of research on differentially expressed miRNAs (DEMs) related to liver infection induced by H. meleagridis. In this study, the weight gain and pathological changes at various post-infection time points were evaluated through animal experiments to determine the peak and early stages of infection. Next, High-throughput sequencing was used to examine the expression profile of liver miRNA at 10 and 15 days post-infection (DPI) in chickens infected with the Chinese JSYZ-F strain of H. meleagridis. A comparison with uninfected controls revealed the presence of 120 and 118 DEMs in the liver of infected chickens at 10 DPI and 15 DPI, respectively, with 74 DEMs being shared between the two time points. Differentially expressed microRNAs (DEMs) were categorized into three groups based on the time post-infection. The first group (L1) includes 45 miRNAs that were differentially expressed only at 10 DPI and were predicted to target 1646 genes. The second group (L2) includes 43 miRNAs that were differentially expressed only at 15 DPI and were predicted to target 2257 genes. The third group (L3) includes 75 miRNAs that were differentially expressed at both 10 DPI and 15 DPI and were predicted to target 1623 genes. At L1, L2, and L3, there were 89, 87, and 41 significantly enriched Gene Ontology (GO) terms, respectively (p<0.05). The analysis of differentially expressed miRNA target genes using KEGG pathways revealed significant enrichment at L1, L2, and L3, with 3, 4, and 5 pathways identified, respectively (p<0.05). This article suggests that the expression of liver miRNA undergoes dynamic alterations due to H. meleagridis and the host. It showed that the expression pattern of L1 class DEMs was more conducive to regulating the development of the inflammatory response, while the L2 class DEMs were more conducive to augmenting the inflammatory response. The observed patterns of miRNA expression associated with inflammation were in line with the liver's inflammatory process following infection. The results of this study provide a basis for conducting a comprehensive analysis of the pathogenic mechanism of H. meleagridis from the perspective of host miRNAs.

Concurrent Histomonas meleagridis and Hemorrhagic Enteritis Virus Infection in a Turkey Flock with Recurrent History of Blackhead Disease

Intestinal health is one of the key factors required for the growth and production of turkeys. Histomoniasis (blackhead disease), caused by a protozoan parasite, Histomonas meleagridis, is a reemerging threat to the turkey industry. Increased incidences of histomoniasis have been reported in recent years due to withdrawal of antihistomonas treatments. H. meleagridis affects ceca and causes cecal inflammation and necrosis. H. meleagridis migrates from ceca to the liver and causes liver necrosis, resulting in high mortalities. Ironically, field outbreaks of histomoniasis are not always associated with high mortalities, while low mortalities have also been documented. There are several exacerbating factors associated with high mortality rates in histomoniasis outbreaks, with concurrent infection being one of them. Recurrent histomoniasis outbreaks in a newly constructed barn were documented, and concurrent infection of H. meleagridis and hemorrhagic enteritis virus was confirmed. Currently, neither commercial vaccines nor prophylactic or therapeutic solutions are available to combat histomoniasis. However, there are treatments, vaccines, and solutions to minimize or prevent concurrent infections in turkeys. In addition to implementing biosecurity measures, measures to prevent concurrent infections are critical steps that the turkey industry can follow to reduce mortality rates and minimize the production and economic losses associated with histomoniasis outbreaks.

Antimicrobial Peptides (AMP) in the Cell-Free Culture Media of Xenorhabdus budapestensis and X. szentirmaii Exert Anti-Protist Activity against Eukaryotic Vertebrate Pathogens including Histomonas meleagridis and Leishmania donovani Species

Anti-microbial peptides provide a powerful toolkit for combating multidrug resistance. Combating eukaryotic pathogens is complicated because the intracellular drug targets in the eukaryotic pathogen are frequently homologs of cellular structures of vital importance in the host organism. The entomopathogenic bacteria (EPB), symbionts of entomopathogenic-nematode species, release a series of non-ribosomal templated anti-microbial peptides. Some may be potential drug candidates. The ability of an entomopathogenic-nematode/entomopathogenic bacterium symbiotic complex to survive in a given polyxenic milieu is a coevolutionary product. This explains that those gene complexes that are responsible for the biosynthesis of different non-ribosomal templated anti-microbial protective peptides (including those that are potently capable of inactivating the protist mammalian pathogen Leishmania donovanii and the gallinaceous bird pathogen Histomonas meleagridis) are co-regulated. Our approach is based on comparative anti-microbial bioassays of the culture media of the wild-type and regulatory mutant strains. We concluded that Xenorhabdus budapestensis and X. szentirmaii are excellent sources of non-ribosomal templated anti-microbial peptides that are efficient antagonists of the mentioned pathogens. Data on selective cytotoxicity of different cell-free culture media encourage us to forecast that the recently discovered "easy-PACId" research strategy is suitable for constructing entomopathogenic-bacterium (EPB) strains producing and releasing single, harmless, non-ribosomal templated anti-microbial peptides with considerable drug, (probiotic)-candidate potential.

Investigations of Histomonosis-Favouring Conditions: A Hypotheses-Generating Case-Series-Study

Since the ban of effective feed additives and therapeutics, histomonosis has become an important disease and, subsequently, a welfare issue for turkey production. We conducted an interview-based case series study to generate hypotheses about possible disease-favouring conditions in 31 H. meleagridis-infected flocks. The determined parameters were related to the general farm (flock management, biosecurity measures, etc.) as well as the histomonosis-specific disease management. Some inadequate biosecurity measures were observed. An inappropriate usage of the hygiene lock and cleaning as well as the disinfection frequency of equipment, clothes, and the hygiene lock could possibly be histomonosis-favouring conditions. These factors could increase the risk for the introduction of H. meleagridis and the risk of a pathogen spread on an affected farm. Insects, wild birds, litter materials, and contaminated dung could be potential vectors of H. meleagridis. Predisposing gastrointestinal diseases were observed in 71% of the affected flocks. Additionally, stress events related to higher temperature, movement of birds, and vaccination were documented in association with clinical histomonosis. The results emphasise the need for both good disease control and health management to ensure sustainable animal health and welfare.

Tandem mass tag-based quantitative proteomics analyses of a chicken-original virulent and its attenuated Histomonas meleagridis strain in China

Introduction

Histomonas meleagridis can cause histomonosis in poultry. Due to the prohibition of effective drugs, the prevention and treatment of the disease requires new strategies. Questions about its pathogenic mechanisms and virulence factors remain puzzling.

Methods

To address these issues, a tandem mass tag (TMT) comparative proteomic analysis of a virulent strain and its attenuated strain of Chinese chicken-origin was performed.

Results

A total of 3,494 proteins were identified in the experiment, of which 745 proteins were differentially expressed (fold change ≥1.2 or ≤0.83 and p &lt; 0.05), with 192 up-regulated proteins and 553 down-regulated proteins in the virulent strain relative to the attenuated strain.

Discussion

Surface protein BspA like, digestive cysteine proteinase, actin, and GH family 25 lysozyme were noted among the proteins up regulated in virulent strains, and these several proteins may be directly related to the pathogenic capacity of the histomonad. Ferredoxin, 60S ribosomal protein L6, 40S ribosomal protein S3, and NADP-dependent malic enzyme which associated with biosynthesis and metabolism were also noted, which have the potential to be new drug targets. The up-regulation of alpha-amylase, ras-like protein 1, ras-like protein 2, and involucrin in attenuated strains helps to understand how it is adapted to the long-term in vitro culture environment. The above results provide some candidate protein-coding genes for further functional verification, which will help to understand the molecular mechanism of pathogenicity and attenuation of H. meleagridis more comprehensively.

Retrospective Investigations of Recurring Histomonosis on a Turkey Farm

The ban of effective feed additives and therapeutics in the European Union and in other parts of the world led to a dramatic increase of histomonosis in turkeys. Despite the impact of the disease on the health and welfare of poultry, many questions remain open regarding the epidemiology of the pathogen. In this study, we retrospectively monitored a farm with recurring cases of histomonosis to identify possible routes of pathogen introduction and predisposing factors that may influence the disease development. We included 32 consecutive turkey flocks, which were fattened between 2007 and 2021 on the same farm under the same management and housing conditions. During this period, Histomonas meleagridis was detected in eight flocks of toms and four flocks of hens with a high variability in disease development. Outbreaks in toms led to significantly (P ≤ 0.05) higher mortality rates (5.3%-98.3%) than in hens (2.6%-6.1%). Most of the outbreaks (9/12) were diagnosed between June and September with a peak in August, suggesting a possible impact of higher temperatures either on the host or on the pathogen and pathogen-transmitting vectors. Further investigation is necessary to determine why hens might cope better with histomonosis than toms. Continuous flock and hygiene management is important to prevent an introduction of the causative pathogen and to control potential vectors.

Genetic resilience in chickens against bacterial, viral and protozoal pathogens

The genome contributes to the uniqueness of an individual breed, and enables distinctive characteristics to be passed from one generation to the next. The allelic heterogeneity of a certain breed results in a different response to a pathogen with different genomic expression. Disease resistance in chicken is a polygenic trait that involves different genes that confer resistance against pathogens. Such resistance also involves major histocompatibility (MHC) molecules, immunoglobulins, cytokines, interleukins, T and B cells, and CD4+ and CD8+ T lymphocytes, which are involved in host protection. The MHC is associated with antigen presentation, antibody production, and cytokine stimulation, which highlight its role in disease resistance. The natural resistance-associated macrophage protein 1 (Nramp-1), interferon (IFN), myxovirus-resistance gene, myeloid differentiation primary response 88 (MyD88), receptor-interacting serine/threonine kinase 2 (RIP2), and heterophile cells are involved in disease resistance and susceptibility of chicken. Studies related to disease resistance genetics, epigenetics, and quantitative trait loci would enable the identification of resistance markers and the development of disease resistance breeds. Microbial infections are responsible for significant outbreaks and have blighted the poultry industry. Breeding disease-resistant chicken strains may be helpful in tackling pathogens and increasing the current understanding on host genetics in the fight against communicable diseases. Advanced technologies, such as the CRISPR/Cas9 system, whole genome sequencing, RNA sequencing, and high-density single nucleotide polymorphism (SNP) genotyping, aid the development of resistant breeds, which would significantly decrease the use of antibiotics and vaccination in poultry. In this review, we aimed to reveal the recent genetic basis of infection and genomic modification that increase resistance against different pathogens in chickens.

Comparative Surfaceome Analysis of Clonal Histomonas meleagridis Strains with Different Pathogenicity Reveals Strain-Dependent Profiles

Histomonas meleagridis, a poultry-specific intestinal protozoan parasite, is histomonosis’s etiological agent. Since treatment or prophylaxis options are no longer available in various countries, histomonosis can lead to significant production losses in chickens and mortality in turkeys. The surfaceome of microbial pathogens is a crucial component of host–pathogen interactions. Recent proteome and exoproteome studies on H. meleagridis produced molecular data associated with virulence and in vitro attenuation, yet the information on proteins exposed on the cell surface is currently unknown. Thus, in the present study, we identified 1485 proteins and quantified 22 and 45 upregulated proteins in the virulent and attenuated strains, respectively, by applying cell surface biotinylation in association with high-throughput proteomic analysis. The virulent strain displayed upregulated proteins that could be linked to putative virulence factors involved in the colonization and establishment of infection, with the upregulation of two candidates being confirmed by expression analysis. In the attenuated strain, structural, transport and energy production proteins were upregulated, supporting the protozoan’s adaptation to the in vitro environment. These results provide a better understanding of the surface molecules involved in the pathogenesis of histomonosis, while highlighting the pathogen’s in vitro adaptation processes.

Feed Composition and Isolate of Histomonas meleagridis Alter Horizontal Transmission of Histomonosis in Turkeys. Proof of Concept

Outbreaks of histomonosis in turkeys are typically initiated by the ingestion of contaminated embryonated eggs of Heterakis gallinarum, potentially present in earthworms and mechanical vectors. Once an outbreak is started, infected turkeys can transmit the disease by horizontal transmission. Factors influencing horizontal transmission of histomonosis are poorly understood. Replication of horizontal transmission in experimental conditions has not been consistent, presenting an obstacle in searching for alternatives to prevent or treat the disease. Two pilot experiments and three validation experiments were conducted in the present study. In pilot experiment 1, one isolate of Histomonas meleagridis (named Buford) was used. Turkeys were fed a low-nutrient density diet corn-soy based (LOW-CS) and raised in floor pens. In pilot experiment 2, another isolate of H. meleagridis was used (named PHL). Turkeys were fed a low-nutrient density diet with the addition of wheat middlings (LOW-WM) and raised in floor pens. In experiment 3, conducted on floor pens, both isolates and diets were used in different groups. In experiment 4, turkeys were raised on battery cages and only the PHL isolate was used. Both diets (LOW-WM and LOW-CS) were used, in addition to a diet surpassing the nutritional needs of young poults (turkey starter, TS). In experiment 5, conducted in battery cages, only the PHL isolate was used, and the LOW-WM and TS diets were in different groups. The horizontal transmission was achieved only with the PHL isolate from all experiments. The transmission rate varied among experimental diets, with the TS diet having the lowest transmission rate in experiments 4 and 5. Variation was observed between experiments and within experimental groups.

MicroRNA expression profile of chicken cecum in different stages during Histomonas meleagridis infection

Background

Histomonas meleagridis is an anaerobic, intercellular parasite, which infects gallinaceous birds such as turkeys and chickens. In recent years, the reemergence of Histomoniasis has caused serious economic losses as drugs to treat the disease have been banned. At present, H. meleagridis research focuses on virulence, gene expression analysis, and the innate immunity of the host. However, there are no studies on the differentially expressed miRNAs (DEMs) associated with the host inflammatory and immune responses induced by H. meleagridis. In this research, high-throughput sequencing was used to analyze the expression profile of cecum miRNA at 10 and 15 days post-infection (DPI) in chickens infected with Chinese JSYZ-F strain H. meleagridis.

Results

Compared with the controls, 94 and 127 DEMs were found in cecum of infected chickens at 10 DPI (CE vs CC) and 15 DPI (CEH vs CCH), respectively, of which 60 DEMs were shared at two-time points. Gene Ontology (GO) functional enrichment analysis of the target genes of DEMs indicated that 881 and 1027 GO terms were significantly enriched at 10 and 15 DPI, respectively. Kyoto Encyclopedia of Genes and Genomes (KEGG, www.kegg.jp/kegg/kegg1.html) pathway enrichment analysis of the target genes of DEMs demonstrated that 5 and 3 KEGG pathways were significantly enriched at 10 and 15 DPI, respectively. For previous uses, the Kanehisa laboratory have happily provided permission. The integrated analysis of miRNA–gene network revealed that the DEMs played important roles in the host inflammatory and immune responses to H. meleagridis infection by dynamically regulating expression levels of inflammation and immune-related cytokines.

Conclusion

This article not only suggested that host miRNA expression was dynamically altered by H. meleagridis and host but also revealed differences in the regulation of T cell involved in host responses to different times H. meleagridis infection.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12917-022-03316-2.

Histomonosis in Poultry: A Comprehensive Review

Histomonas meleagridis, the etiological agent of histomonosis, is a poultry parasite primarily detrimental to turkeys. Characteristic lesions occur in the liver and ceca, with mortalities in turkey flocks often reaching 80-100%. Chickens and other gallinaceous birds can be susceptible but the disease was primarily considered sub-clinical until recent years. Treating and preventing H. meleagridis infection have become more difficult since 2015, when nitarsone was voluntarily removed from the market, leaving the poultry industry with no approved prophylactics, therapeutics, or vaccines to combat histomonosis. Phytogenic compounds evaluated for chemoprophylaxis of histomonosis have varied results with in vitro and in vivo experiments. Some recent research successes are encouraging for the pursuit of antihistomonal compounds derived from plants. Turkeys and chickens exhibit a level of resistance to re-infection when recovered from H. meleagridis infection, but no commercial vaccines are yet available, despite experimental successes. Safety and stability of live-attenuated isolates have been demonstrated; furthermore, highly efficacious protection has been conferred in experimental settings with administration of these isolates without harming performance. Taken together, these research advancements are encouraging for vaccine development, but further investigation is necessary to evaluate proper administration age, dose, and route. A summary of the published research is provided in this review.

Worm control practices on free-range egg farms in Australia and anthelmintic efficacy against nematodes in naturally infected layer chickens

This study investigated worm control practices by free-range egg farmers and the efficacy of the commercial anthelmintics levamisole (LEV), piperazine (PIP), flubendazole (FLBZ) and fenbendazole (FBZ) against gastrointestinal nematodes on two free-range layer farms in Australia. An online survey comprising 36 questions was designed and implemented using SurveyMonkey. The survey contained questions about participant demographics, farm and flock characteristics, perceived intestinal worm importance, infection monitoring, deworming and other worm control practices. A link for the survey was emailed to free range egg producers from their industry body in December 2019. The anthelmintic efficacy trial was conducted in a total of 229 layers naturally infected with Ascaridia galli, Hetarakis gallinarum, Capillaria spp. and/or tape worms. Chickens received a single oral dose of LEV (28 mg/kg), PIP (100 mg/kg), FBZ (10 mg/kg) or LEV-PIP co-administered at their full individual doses, and FLBZ (Flubenol®), 30 ppm or 60 ppm) in the feed over 7 days. Anthelmintic efficacies were estimated by both worm count reduction (WCR %) and excreta egg count reduction (EECR %) tests 10 days after start of treatment. The survey with a response rate of 16/203, revealed that worm infection was of moderate concern to the producers and the majority (68%) felt that the current anthelmintics work effectively. The level of understanding of worms, monitoring and control practices did not reveal any major deficiencies of concern. The most commonly used anthelmintic was LEV (73%) followed by PIP (45%). Based on a standard cut-off value (≥90%), LEV, LEV-PIP, and FBZ attained the desired efficacy but PIP exhibited reduced efficacy against immature A. galli (61-85%), all stages of H. gallinarum (42-77%) and Capillaria spp. (25-44%). FLBZ was highly effective against all stages of roundworms and tapeworm infections. Even though there was some association between the efficacies estimated by WCR % and EECR % the latter was poorly associated in the natural infection model and hence does not provide a reasonable alternative for assessing anthelmintic efficacy when immature stages of the lifecycle are included. These results show no evidence of loss of susceptibility to the tested anthelmintics on these farms supporting the perception of producers that participated in the survey that current treatments work effectively. The reduced efficacy of PIP against some species and immature stages is related to its spectrum of activity rather than providing evidence of emerging resistance.

Prevalence and diversity of intestinal parasites in household and temple pigeons ( Columba livia ) in central Nepal

Background

Intestinal infection, caused by various protozoans and helminths, represents one of the significant health concerns in pigeons around the world.

Objectives

The present study aimed to determine the diversity and prevalence of the intestinal parasites in pigeons found in Ratnanagar Municipality, Chitwan, in central Nepal.

Methods

The fresh faecal samples (n = 155) were non‐invasively collected from different households and temples pigeons The individual samples were immediately preserved in the 2.5% potassium dichromate solution and transported to the research laboratory. Following direct wet mount and concentration methods, the samples were observed under a compound microscope.

Results

The results showed 87.1% prevalence rate with 16 parasite species that included 8 protozoan and 8 helminth faunae. The faecal samples of temple pigeons contained a higher prevalence rate with higher parasitic richness (95.6%; 16 species) than household pigeons (75.4%; 12 species). Mixed infection up to four different species was recorded in both types of sampling populations.

Conclusions

Pigeons harbour a greater prevalence and wider diversity of intestinal parasites and the parasitism varies based on the habitats. Proper management and effective deworming practices are recommended to control intestinal parasitic infection in these avian hosts.

Pathomorphological and molecular investigations in naturally infected Chukar partridges (Alectoris Chukar) with Histomonas meleagridis and Tetratrichomonas gallinarum

ABSTRACT: Histomonas meleagridis and Tetratrichomonas gallinarum are two protozoans responsible for mortality associated with typhlohepatitis in poultry. In this study, the etiology of high mortality in Chukar partridges suspected of infection with these agents was investigated pathologically and molecularly. Twelve healthy partridges during the laying period and 30 partridges that died due to disease and were included in the study. In blood analysis, increased levels of WBC, NEU, LYM, MONO, EO and BASO suggesting bacterial and/or parasitic infection; decreased levels of HGB, MCH and MCHC, which are markers of anemia; and increased AST and LDH levels, which are important for liver degenerations. In the liver, which is one of the most pathologically affected organs, multifocal necrosis foci that sometimes merge with each other and spread to large areas, and severe fibrino-necrotic typhlitis were detected. There was amyloid deposition in the space of Disse and vascular sinuses in the liver. PAS positive protozoal agents were observed in and around the lesioned areas. By PCR analyzes using specific primers, 11 of the samples were positive for H. meleagridis only, whereas 5 were positive for T. gallinarum only; 14 samples tested positive for both agents. Sequence analysis showed 100% identity between all samples resulting in positive PCR. In addition, Escherichia coli was produced in microbiological culture (27 of 30). When all the results were evaluated together, it was concluded that H. meleagridis and T. gallinarum and secondary E. coli may cause high mortality in partridges under lay stress.

Evaluation of live-attenuated Histomonas meleagridis isolates as vaccine candidates against wild-type challenge

Repeated serial in vitro passage of Histomonas meleagridis, the etiological agent of histomoniasis (blackhead) of turkeys, was demonstrated to markedly achieve attenuation and reduction of virulence as compared to the original wild-type isolate. Four experiments were performed to evaluate the route (oral vs. intracloacal) and age (day-of-hatch vs. d 14) for administration of attenuated H. meleagridis isolates as vaccine candidates against homologous or heterologous wild-type challenge. Attenuated H. meleagridis were developed from 2 different strains (Buford strain originating in Georgia; PHL2017 strain originating in Northwest Arkansas). Buford P80a (passage 80, assigned as isolate lineage “a” following repeated passage) was selected as the primary vaccine candidate and was evaluated in Experiments 1–3. Experiment 4 evaluated selected candidates of attenuated PHL2017 (P67, P129) and Buford (P80a, P200a, P138b, P198c) strains against Buford wild-type challenge. As has been demonstrated previously, wild-type H. meleagridis cultures administered orally after 1 day of age were not infective in the current studies, but infection with wild-type cultures could be induced orally at day-of-hatch. Infection was effectively achieved via the intracloacal route at day-of-hatch and in older turkeys (d 21, d 28–29, d 35). Intracloacal inoculation of turkeys with the attenuated passaged isolates as vaccine candidates at d 14 was shown to produce significant (P < 0.05) protection from mortality, reduction in body weight gain, as well as reduction in hepatic and cecal lesions in these experiments following challenge with either the homologous wild-type isolate or from a wild-type strain obtained years later from a geographically disparate area of the United States. Inoculation with the attenuated H. meleagridis isolates at day-of-hatch, either orally or cloacally, did not produce significant protection against subsequent wild-type challenge. While offering significant protection with minimal vaccine-related negative effects, the protection from cloacal vaccine administration was neither significantly robust nor encouraging for industry application using the methods evaluated in the present manuscript since mortalities and lesions were not completely reduced which could thereby potentially allow transmission from residual infection and shedding within a flock.

Heterakis gallinarum and Histomonas meleagridis DNA persists in chicken houses years after depopulation

The poultry pathogen Histomonas meleagridis is transmitted by chicken cecal worms (Heterakis gallinarum) and is potentially transmitted by second order insect vectors and paratenic hosts. Darkling beetles (Alphitobius diaperinus) are poultry farm pests that infest barns. An outstanding question is the degree to which darkling beetles transmit both Heterakis and Histomonas. In this study we monitored populations of darkling beetles and assessed their positivity for both Heterakis and Histomonas by PCR. Uniquely, this study was conducted during the scheduled deconstruction of Auburn University's Poultry Research Farm. Therefore, we were able to monitor beetle and litter infection status months and years after bird depopulation. The duration of our monitoring continued through three seasons. We show that environmental DNA from both Heterakis and Histomonas persist in the environment long after prior infections, even in the absence of living Heterakis and its hosts. Finally, in an intensive search for live Heterakis, we discovered reniform nematodes (plant parasitic nematodes) residing in the soil floor of poultry farms.

Excretion of Histomonas meleagridis following experimental co-infection of distinct chicken lines with Heterakis gallinarum and Ascaridia galli

Background

Histomonosis is a severe re-emerging disease of poultry caused by Histomonas meleagridis, a protozoan parasite which survives in the environment via the cecal worm Heterakis gallinarum. Following infection, the parasites reside in the ceca and are excreted via host feces. In the present work, male birds of conventional broiler (Ross 308, R), layer (Lohmann Brown Plus, LB) and a dual-purpose (Lohmann Dual, LD) chicken line were infected with 250 embryonated eggs of Ascaridia galli and Heterakis gallinarum, respectively, with the latter nematode harboring Histomonas meleagridis, to investigate a co-infection of nematodes with the protozoan parasite in different host lines.

Methods

In weekly intervals, from 2 to 9 weeks post infection (wpi), individual fecal samples (n = 234) from the chickens were collected to quantify the excretion of H. meleagridis by real-time PCR and to determine the number of nematode eggs per gram (EPG) in order to elucidate excretion dynamics of the flagellate and the nematodes. This was further investigated by indirect detection using plasma samples of the birds to detect antibodies specific for H. meleagridis and worms by ELISA. The infection with H. meleagridis was confirmed by histopathology and immunohistochemistry to detect the flagellate in the cecum of representing birds.

Results

The excretion of H. meleagridis could already be observed from the 2nd wpi in some birds and increased to 100% in the last week of the experiment in all groups independent of the genetic line. This increase could be confirmed by ELISA, even though the number of excreted H. meleagridis per bird was generally low. Overall, histomonads were detected in 60% to 78% of birds with temporary differences between the different genetic lines, which also showed variations in the EPG and worm burden of both nematodes.

Conclusions

The infection with H. gallinarum eggs contaminated with H. meleagridis led to a permanent excretion of the flagellate in host feces. Differences in the excretion of H. meleagridis in the feces of genetically different host lines occurred intermittently. The excretion of the protozoan or its vector H. gallinarum was mostly exclusive, showing a negative interaction between the two parasites in the same host.

Graphic abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13071-021-04823-1.

A novel duplex ddPCR assay for detection and differential diagnosis of Ascaridia galli and Heterakis gallinarum eggs from chickens feces

Since the EU ban on battery cages, many studies have listed Ascaridia galli and Heterakis gallinarum as the most common roundworms in the European laying hen population. A complicating factor is that the eggs of these parasites are almost identical. Thus, lack of molecular diagnostic approaches has driven epidemiological studies to take on necropsy for species discrimination, which is labor and cost intensive. Here, we describe a novel diagnostic tool based on droplet digital PCR for simultaneous identification and absolute quantification of the eggs of both of these ascarids in chickens' droppings using two different genus-specific primer-probe sets targeting the second internal transcribed spacer region (ITS-2) in the nuclear ribosomal (rRNA) gene array. No cross-reaction was observed when different combinations of DNA and species-specific primers and probes were tested. The lowest obtained frequency threshold for the detection of H. gallinarum in the presence of a constant A. galli DNA concentration was determined to be 0.8 %. After validation, we used the assay to analyze field samples collected from several Swedish laying hen farms. Out of 134 samples, 86 (64 %) were positive for A. galli while 11 (8.3 %) samples were positive for H. gallinarum. These samples were initially analyzed with flotation technique for detection of ascarid eggs. The results of the Cohen's kappa indicated substantial agreement (85.8 %) between the two tests. In conclusion, we have validated a novel molecular-based diagnostic tool for quantification and differentiation between intestinal parasites of major importance in chickens with high precision. Although this study focuses on identification of parasites of laying hens, the findings may well have a bearing on all types of chicken production systems. The present study lays the groundwork for future research into epidemiology of these two important chicken parasite species.

Phytoncides in The Prevention and Therapy of Blackhead Disease and Their Effect on The Turkey Immune System

Introduction

Turkey histomonosis poses a serious threat to poultry production due to the ban on the use of effective drugs. The aim of the study was to evaluate the influence of a phytoncidal feed supplement on the course of histomonosis. The preparation was also analysed for immunomodulatory properties.

Material and Methods

Clinical observations and production monitoring were conducted in a flock of turkeys with histomonosis from their 11^th to 56^th weeks of life which were treated with the adiCox^SOLPF soluble supplement in a dose of 2.5 mL/L water. Later the preparation was used in a preventive dose (1 mL/L). The influence on the immune system was evaluated in broiler turkeys having been given adiCox^SOLPF for 3 days in doses of 1 or 3 mL/L. The T and B lymphocyte percentages in turkey blood and spleen tissue were analysed with flow cytometry. ELISA was implemented to evaluate antibody titres after Ornithobacterium rhinotracheale vaccination, and biochemical analyses were performed to evaluate the supplement's safety.

Results

AdiCox^SOLPF was found effective in therapy and prevention of histomonosis. Additionally, adiCox^SOLPF stimulated both humoral and cell-mediated immune mechanisms, without impairing the functions of internal organs. The treated turkeys also yielded better production results (eggs/hen, fertility, and hatchability).

Conclusion

AdiCox^SOLPF possesses immunomodulatory properties and it can be used successfully in the prevention and therapy of histomonosis in turkeys.

Histomonas meleagridis isolates compared by virulence and gene expression

Pathology and putative virulence factor expression of three Histomonas meleagridis isolates differing in geographic origin, cell passage number (56 or 100), or cell populations grown from a monoculture were compared. Turkey poults inoculated with the high cell passage number isolates or monoculture isolates varied in gross lesion severity and weight gain (P<0.0001). Screening of a published H. meleagridis cDNA library identified forty- eight cysteine proteinases (CP) and one superoxide dismutase (Fe-SOD) proposed to function in either tissue damage and/or invasion and oxidative defense. The Fe-SOD and eight CPs were analyzed using real time polymerase chain reaction. CP2, CP3, and CP8 showed significant differences in expression among the field isolates (P ≤ 0.05). The high passage isolates had decreased CP2, CP3 and CP4 expression when compared with their field isolate. CP7 did not differ between field isolates or the 56-passaged isolate. The Fe-SOD gene showed significant differences in expression among the various isolates. When exposing cultured H. meleagridis to air, Fe-SOD expression decreased rapidly during the first hour of air exposure but increased progressively through the next 3 h. This study provides information on gross pathology and virulence factors associated with various isolates of Histomonas meleagridis which can aid in determining the pathogenetic mechanisms used by this organism.

Research Note: Evaluation of deoxycholic acid for antihistomonal activity

Deoxycholic acid (DCA) is a naturally occurring secondary bile acid that originates from intestinal bacterial metabolic conversion of cholate, a primary bile acid. Deoxycholic acid was shown to have antihistomonal properties in vitro, leading to our hypothesis that DCA inclusion within the feed might prevent histomoniasis. Selected dietary concentrations of DCA were evaluated for effects on body weight gain (BWG), lesions, and mortality of turkeys challenged with wild-type Histomonas meleagridis (WTH). Treatments consisted of non-challenged control (NC; basal diet), 0.25% DCA diet + challenge, 0.5% DCA diet + challenge, 1% DCA diet + challenge, and a positive-challenged control (PC; basal diet). All groups were fed a basal starter diet until day 7, at which time DCA diets were administered to the respective groups. On day 14, 2 × 10⁵ WTH cells/turkey were intracloacally administered. H. meleagridis-related lesions were evaluated on day 13 post-challenge. Pre-challenge day 0 to 14 BWG was higher (P ≤ 0.05) in the 0.25% DCA group than in the 1% DCA group. There were no significant differences in pre-challenge day 0 to 14 BWG between any of the other groups. No significant differences in mortalities from histomoniasis occurred in the DCA groups as compared to the PC group. No H. meleagridis lesions or mortalities were observed at any time in the NC group. Presence of H. meleagridis-related liver lesions was higher (P ≤ 0.05) in the 0.5% DCA group as compared to the PC group. Using the same controls and experimental timeline, an additional group was included to evaluate a biliogenic diet formulated with 20% whole egg powder to encourage endogenous bile acid production. The biliogenic diet had no statistical impact on pre-challenge day 0 to 14 BWG, but did not reduce H. meleagridis-related mortalities or lesions after the challenge. Taken together, these data suggest that DCA inclusion within the feed at these concentrations and under these experimental conditions does not prevent histomoniasis.

Early infection with Histomonas meleagridis has limited effects on broiler breeder hens' growth and egg production and quality

A study was conducted to determine differences between Histomonas meleagridis–infected and control pullets based on disease signs, hen growth, and egg production and quality. Ross 708SF females were weighed and then placed in pens on the day of hatch (92 chicks/pen). At 25 D, 4 pens were infected with H. meleagridis in the cloaca, whereas 4 pens were control. At 5, 10, and 20 D after inoculation, 5 birds per pen (2 birds per pen at 20 D) were subjectively scored for blackhead disease. Birds were feed restricted based on BW and/or egg production. Individual BW were collected at 3, 5, 13, 15, 20, and 64 wk. Egg production was recorded at 24–63 wk. Egg quality was measured at 30, 34, 39, 42, and 56 wk and included shell and vitelline membrane strength, shell thickness, egg weight, and Haugh units. Hatchability was measured at 27, 37, and 60 wk and fertility at 27 and 37 wk. Treatment effects were determined by JMP Pro 14 using GLM with means separated using the Student t test (P ≤ 0.05). Cecal lesions were apparent on 5, 10, and 20 D and liver lesions on 10 and 20 D for the infected birds. The control had no histomoniasis lesions. Flock uniformity differed on wk 13 and 20 (P = 0.04; 0.04). Infected birds weighed less at 64 wk (P = 0.002). The onset of lay was not delayed. Infected birds produced more eggs during 1 period (P = 0.02). The infected birds produced heavier eggs at 30 wk (P = 0.04), eggs with a stronger and thicker shell at 42 wk (P = 0.05, 0.03), and eggs with a stronger vitelline membrane at 56 wk (P = 0.049). Hatchability and fertility did not differ (P > 0.05). H. meleagridis was observed in the infected birds' cecal samples at trial termination. This study indicates early infection with H. meleagridis has limited effects on pullet egg production and quality.

Germination capacity of the Pochonia chlamydosporia fungus after its passage through the gastrointestinal tract of domestic chickens (Gallus gallus domesticus)

This study evaluated the germination capacity of Pochonia chlamydosporia (VC4) fungus after its passage through the gastrointestinal tract of domestic chickens and its interaction with Ascaridia galli and Heterakis gallinarum eggs. Twenty-two domestic chickens were divided in two groups: control group (G1) received shredded corn substrate without VC4; and treatment group (G2) received a single dose of 29 g corn substrate containing 3.3 × 10⁶ conidia/chlamydospores (VC4). Subsequently, chicken fecal samples were collected at intervals of 0, 6, 8, 10, 12, 18 and 24 h. Petri dishes from fecal samples of the treated group (G2) were subdivided (G2a and G2b), and then replicated in 2% agar-water medium for the microbiological test. After VC4 growth, approximately 200 eggs of A. galli (G2a) and H. gallinarum (G2b) were added to each subgroup to evaluation of ovicidal activity. There was fungal viability after passage through chicken gastrointestinal tract and egg predation of 59.9% and 43.2% for A. galli and H. gallinarum, respectively. The present work demonstrates the ability of the fungus P. chlamydosporia to survive after passing through the gastrointestinal tract of domestic chickens, an extreme environment (low pH, enzymes, microbiota and mechanical action), and still germinate after being excreted with feces.

Research Note: Evaluation of dietary administration of sodium chlorate and sodium nitrate for Histomonas meleagridis prophylaxis in turkeys

Histomoniasis is currently a re-emerging disease of major significance for many commercial turkey and broiler breeder production companies because of the unavailability of drugs or vaccines. The protozoa Histomonas meleagridis (HM) requires the presence of enteric microflora to promote the disease. The objectives of this research note were to evaluate the effect of dietary administration of sodium chlorate (SC) and sodium nitrate (SN) in vitro and in vivo for HM prophylaxis in poults. A total of 128 day-of-hatch female poults obtained from a commercial hatchery were wing-tagged and randomly assigned into 1 of 4 experimental groups: negative control (NC), positive control, dietary inclusion of SC (3,200 ppm) and SN (500 ppm). Poults from groups SC and SN started on their respective diets on day 12. All groups, except the NC, were challenged with 2 × 105 HM on day 19. Controls were fed a basal diet, identical to the treatment diets but not supplemented with SC or SN. Body weight gain (BWG) was determined weekly, starting on day 1 until day 28, and postchallenge morbidity and mortality were recorded. On day 28 of age, all surviving poults were lesion scored for hepatic and cecal lesions. Ceca and distal ileum were collected on day 28 for bacterial recovery on selective media for total aerobic, lactic acid bacteria, or gram-negative bacteria. The addition of SC and SN in the in vitro growth of HM greatly reduced the growth of the protozoa after 20 h of incubation when compared with the control nontreated group (P < 0.05). However, dietary supplementation of SC and SN had no effect against HM in vivo, as was demonstrated by BWG, the severity of lesions in the liver and ceca or bacterial recovery of treated poults when compared with the positive control group.

Interplay between Histomonas meleagridis and Bacteria: Mutualistic or Predator-Prey?

Histomonas meleagridis is an extracellular protozoan parasite and the aetiological agent of histomonosis, an important poultry disease whose impact is greatly accentuated by inaccessibility of any treatment. A special feature of the parasite is its intricate interplay with bacteria in vitro and in vivo, the focus of this article.

Characterisation of gastrointestinal helminths and their impact in commercial small-scale chicken flocks in the Mekong Delta of Vietnam

Commercial small-scale chicken farms managed as all-in-all-out but operating with low standards of hygiene/biosecurity are increasingly common in Vietnam. These conditions facilitate the transmission of gastrointestinal helminths. However, there are no published data on helminths in these systems. We aimed (1) to determine the prevalence/burden of gastrointestinal helminths in small-scale commercial flocks in the Mekong Delta region and (2) to investigate the association between worm burdens and birds' weight and disease status. Randomly selected chickens (n = 120) from 'normal' flocks were investigated at the end of their production cycle (~ 18 weeks), as well as 90 chickens from 'diseased' flocks with signs of respiratory and/or severe disease. The gastrointestinal tract of chickens was dissected and all visible helminths were identified and counted. A total of 54.2% and 54.4% normal and diseased chickens contained helminths. Among colonised birds, the diseased ones harboured a higher mass of helminth worms than normal (healthy) birds (3.8 ± SD 8.6 g vs. 1.9 ± SD 6.3 g, respectively). Eight species were identified, including nematodes (Ascaridia galli, Cheilospirura hamulosa and Heterakis gallinarum), cestodes (Hymenolepis, Raillietina cesticillus, Raillietina echinobothrida, Raillietina tetragona,) and one trematode (Echinostomatidae). Heterakis gallinarum was the most prevalent helminth (43.3% and 42.2% in normal and sick chickens, respectively), followed by A. galli (26.7% and 41.1%). Colonised chickens weighed 101.5 g less than non-colonised birds. Colonisation was higher during the rainy months (May-November) for both H. gallinarum and A. galli. Anthelminthic usage was not associated with reduced helminth burdens. We recommend upgrading cleaning and disinfection and limiting access to ranging areas to control helminths in small-scale chicken flocks.

π-Hole Interactions Involving Nitro Aromatic Ligands in Protein Structures

Studying noncanonical intermolecular interactions between a ligand and a protein constitutes an emerging research field. Identifying synthetically accessible molecular fragments that can engage in intermolecular interactions is a key objective in this area. Here, it is shown that so-called "π-hole interactions" are present between the nitro moiety in nitro aromatic ligands and lone pairs within protein structures (water and protein carbonyls and sulfurs). Ample structural evidence was found in a PDB analysis and computations reveal interaction energies of about -5 kcal mol-1 for ligand-protein π-hole interactions. Several examples are highlighted for which a π-hole interaction is implicated in the superior binding affinity or inhibition of a nitro aromatic ligand versus a similar non-nitro analogue. The discovery that π-hole interactions with nitro aromatics are significant within protein structures parallels the finding that halogen bonds are biologically relevant. This has implications for the interpretation of ligand-protein complexation phenomena, for example, involving the more than 50 approved drugs that contain a nitro aromatic moiety.

Epidemic Characteristics of Clinical Histomoniasis in Chicken Flocks in Eastern China

Preliminary diagnosis of clinical symptoms and gross lesions with subsequent histopathologic and PCR analyses revealed histomoniasis in 276 chicken flocks in Jiangsu Province, China, and surrounding areas from January 2012 to December 2015. Detailed statistical analysis was performed to explore the occurrence and epidemic characteristics of histomoniasis in chicken flocks. The results indicated that histomoniasis usually occurred in free-range flocks of local broilers and laying hens. Also, 2- to 3-mo-old chickens were most susceptible to infection, and adult chickens rarely developed infection. The morbidity rate of chickens was generally 10%-30%, with mortality rates of less than 10%. Moreover, histomoniasis is a seasonal disease, occurring most often from April to June, and the rate of coinfection with heterakids in the ceca of infected chicken was 50.8%. The symptoms of diseased chickens included mental fatigue, bowing of the head and wings, and yellowish green droppings, with bloody stool in very limited cases. Most of the pathologic changes were characteristic of the disease, but there were also some atypical lesions confirmed by laboratory techniques. In the current study, the histomoniasis epidemic was first investigated in Chinese chicken flocks, and the results provided a useful reference for further study of this disease.

Resistance and tolerance to mixed nematode infections in chicken genotypes with extremely different growth rates

Fast growing broilers are less able to cope with fitness related challenges. As the allocation of metabolic resources may be traded off between performance and defence functions in parasitized hosts, we hypothesized that fast growing broilers are more sensitive to mixed nematode infections compared with slower growing genotypes under the same environmental conditions. Therefore, we compared male birds of genotypes selected for either meat production (Ross-308, R) or egg production (Lohmann Brown Plus, LB) or for both purposes (Lohmann Dual, LD), to assess their resistance and tolerance to mixed nematode infections with Ascaridia galli and Heterakis gallinarum. While infections reduced feed intake in all three genotypes, feed conversion efficiency was not affected. Infections impaired growth performance only in R birds, indicating lower tolerance in the fast growing genotype compared with slower growing LB and LD genotypes. Impaired tolerance in R birds was associated with a relative nutrient scarcity due to an infection-induced lower feed intake. Resistance to experimentally induced infections depended on host genotype as well as on the worm species involved. Overall, the A. galli burden was higher in R than LB, whereas the burden of LD was not different from that of R and LB. In contrast, the H. gallinarum burden of first generation worms was similar in the three genotypes. Susceptibility to re-infection with H. gallinarum was higher in LB than in LD, whereas very low levels of re-infection were observed in R birds. Our data collectively suggest that resistance and tolerance to mixed nematode infections are sensitive to growth rate in chickens. These differences amongst genotypes may partly be associated with a mismatch between the actual nutrient supply and genotype-specific nutrient requirements.

Detection of Histomonas meleagridis DNA in dust samples obtained from apparently healthy meat turkey flocks without effect on performance

Environmental dust samples obtained from 65 turkey flocks in France, of which six suffered from histomonosis whereas the rest remained apparent healthy until the end of production, were tested for the presence of Histomonas meleagridis DNA by recently developed real-time PCR based on the 18S rRNA locus. In order to determine the genotype of detected histomonads, positive samples were further subjected to conventional 18S PCR and sequencing. Additionally, production data of all tested flocks, such as average daily gain, feed conversion ratio and production index, were statistically evaluated and compared to see the effect of positive dust samples in apparently healthy flocks. Histomonad DNA was detected in the dust obtained from all six clinically affected and, surprisingly, in nine apparent healthy flocks. Sequencing of the 18S rRNA gene resulted in only one DNA sample homologous to H. meleagridis whereas 11 others revealed the presence of several other flagellates. Average daily gain and production index were negatively affected in flocks with clinical histomonosis, resulting in significant difference in comparison with the data obtained from clinically healthy flocks independent of the presence of histomonad DNA in the dust. Overall, there was no significant difference following statistical analysis of production parameters between the two last mentioned groups of tested flocks. Altogether, this is the first investigation demonstrating the presence of H. meleagridis DNA in environmental dust samples obtained from clinically unaffected turkey flocks. However, this finding could not be correlated with impact on production based on analysis and comparison of selected production data. RESEARCH HIGHLIGHTS Environmental dust obtained from clinically healthy turkey flocks, in addition to dust from flocks affected by histomonosis, was found positive for the presence of Histomonas meleagridis DNA. Histomonas-positive dust samples in clinically unaffected flocks did not have a negative effect on production parameters. The results demonstrate a wider spread of H. meleagridis DNA in flocks of commercial meat turkeys than previously thought.

An Outbreak of Histomoniasis in Backyard Sanhuang Chickens

Histomonas meleagridis is a facultative anaerobic parasite, which can cause a common poultry disease known as histomoniasis. The species and age of the birds impacts on the susceptibility, with turkey being the most susceptible species. Chickens are less susceptible to H. meleagridis than turkeys and usually serve as reservoir hosts. Here, the diagnosis of an outbreak of histomoniasis in backyard Sanhuang chickens is described. The primary diagnosis was made based on clinical symptoms, general changes at necropsy, histopathology, and the isolation and cultivation of parasites. The pathogen was further confirmed by cloning, PCR identification, and animal inoculation tests. A strain of H. meleagridis, named HM-JSYZ-C, with a higher pathogenicity level in chickens was obtained. The study lays a foundation for further investigations into H. meleagridis and histomoniasis in chickens.

An Alliance of Gel-Based and Gel-Free Proteomic Techniques Displays Substantial Insight Into the Proteome of a Virulent and an Attenuated Histomonas meleagridis Strain

The unicellular protozoan Histomonas meleagridis is notorious for being the causative agent of histomonosis, which can cause high mortality in turkeys and substantial production losses in chickens. The complete absence of commercially available curative strategies against the disease renders the devising of novel approaches a necessity. A fundamental step toward this objective is to understand the flagellate's virulence and attenuation mechanisms. For this purpose we have previously conducted a comparative proteomic analysis of an in vitro cultivated virulent and attenuated histomonad parasite using two-dimensional electrophoresis and MALDI-TOF/TOF. The current work aimed to substantially extend the knowledge of the flagellate's proteome by applying 2D-DIGE and sequential window acquisition of all theoretical mass spectra (SWATH) MS as tools on the two well-defined strains. In the gel-based experiments, 49 identified protein spots were found to be differentially expressed, of which 37 belonged to the in vitro cultivated virulent strain and 12 to the attenuated one. The most frequently identified proteins in the virulent strain take part in cytoskeleton formation, carbohydrate metabolism and adaptation to stress. However, post-translationally modified or truncated ubiquitous cellular proteins such as actin and GAPDH were identified as upregulated in multiple gel positions. This indicated their contribution to processes not related to cytoskeleton and carbohydrate metabolism, such as fibronectin or plasminogen binding. Proteins involved in cell division and cytoskeleton organization were frequently observed in the attenuated strain. The findings of the gel-based studies were supplemented by the gel-free SWATH MS analysis, which identified and quantified 42 significantly differentially regulated proteins. In this case proteins with peptidase activity, metabolic proteins and actin-regulating proteins were the most frequent findings in the virulent strain, while proteins involved in hydrogenosomal carbohydrate metabolism dominated the results in the attenuated one.

Unravelling the Immunity of Poultry Against the Extracellular Protozoan Parasite Histomonas meleagridis Is a Cornerstone for Vaccine Development: A Review

The protozoan parasite Histomonas meleagridis is the causative agent of histomonosis in gallinaceous birds, predominantly in turkeys and chickens. Depending on the host species the outcome of the disease can be very severe with high mortality as observed in turkeys, whereas in chickens the mortality rates are generally lower. The disease is known for more than 100 years when in vitro and in vivo investigations started to understand histomonosis and the causative pathogen. For decades histomonosis could be well-controlled by effective drugs for prevention and therapy until the withdrawal of such chemicals for reasons of consumer protection in Europe, the USA and additional countries worldwide. Consequently, research efforts also focused to find new strategies against the disease, resulting in the development of an efficacious live-attenuated vaccine. In addition to efficacy and safety several studies were performed to obtain a deeper understanding of the immune response of the host against H. meleagridis. It could be demonstrated that antibodies accumulate in different parts of the intestine of chickens following infection with H. meleagridis which was much pronounced in the ceca. Furthermore, expression profiles of various cytokines revealed that chickens mounted an effective cecal innate immune response during histomonosis compared to turkeys. Studying the cellular immune response following infection and/or vaccination of host birds showed a limitation of pronounced changes of B cells and T-cell subsets in vaccinated birds in comparison to non-protected birds. Additionally, numbers of lymphocytes including cytotoxic T cells increased in the ceca of diseased turkeys compared to infected chickens suggesting an immunopathological impact on disease pathogenesis. The identification of type 1 and type 2 T-helper (Th) cells in infected and lymphoid organs by in situ hybridization did not show a clear separation of Th cells during infection but revealed a coherence of an increase of interferon (IFN)-γ mRNA positive cells in ceca and protection. The present review not only summarizes the research performed on the immune response of host birds in the course of histomonosis but also highlights the specific features of H. meleagridis as a model organism to study immunological principles of an extracellular organism in birds.

Alternate routes of influenza A virus infection in Mallard (Anas platyrhynchos)

The natural reservoir for all influenza A viruses (IAVs) is wild birds, particularly dabbling ducks. During the autumn, viral prevalence can be very high in dabbling ducks (> 30%) in the Northern Hemisphere, and individuals may be repeatedly infected. Transmission and infection is through the fecal-oral route, whereby birds shed viruses in feces and conspecifics are infected though feeding in virus-contaminated water. In this study we wanted to assess two alternative infection routes: cloacal drinking and preening. Using experimental infections, we assessed patterns of infection using a combination of virus shedding, as assessed by real-time PCR from cloacal swabs, and patterns of viral replication using virus-immunohistochemistry of gastrointestinal tissues. The cloacal drinking experiment consisted of two trials using cloacal inoculation at two different time points to account for age differences, as well as a trial whereby ducks were allowed to take up virus-laden water through the cloaca. All ducks became infected, and rather than the bursa of Fabricius being the main site of replication, the colon had the highest intensity of replication, as inferred through immunohistochemistry. In experiments assessing preening, feathers were contaminated with virus-laden water and all ducks became infected, regardless of whether they were kept individually or together. Further, naive contacts were infected by the individuals whose feathers were virus-contaminated. Overall, we reinforce that IAV transmission in dabbling ducks is multifactorial-if exposed to virus-contaminated water ducks may be infected through dabbling, preening of infected feathers, and cloacal drinking.

Co-expulsion of Ascaridia galli and Heterakis gallinarum by chickens

Worm expulsion is known to occur in mammalian hosts exposed to mono-species helminth infections, whilst this phenomenon is poorly described in avian hosts. Mono-species infections, however, are rather rare under natural circumstances. Therefore, we quantified the extent and duration of worm expulsion by chickens experimentally infected with both Ascaridia galli and Heterakis gallinarum, and investigated the accompanying humoral and cell-mediated host immune responses in association with population dynamics of the worms. Results demonstrated the strong co-expulsion of the two ascarid species in three phases. The expulsion patterns were characterized by non-linear alterations separated by species-specific time thresholds. Ascaridia galli burden decreased at a daily expulsion rate (e) of 4.3 worms up to a threshold of 30.5 days p.i., followed by a much lower second expulsion rate (e = 0.46), which resulted in almost, but not entirely, complete expulsion. Heterakis gallinarum was able to induce reinfection within the experimental period (9 weeks). First generation H. gallinarum worms were expelled at a daily rate of e = 0.8 worms until 36.4 days p.i., and thereafter almost no expulsion occurred. Data on both humoral and tissue-specific cellular immune responses collectively indicated that antibody production in chickens with multispecies ascarid infections is triggered by Th2 polarisation. Local Th2 immune responses and mucin-regulating genes are associated with the regulation of worm expulsion. In conclusion, the chicken host is able to eliminate the vast majority of both A. galli and H. gallinarum in three distinct phases. Worm expulsion was strongly associated with the developmental stages of the worms, where the elimination of juvenile stages was specifically targeted. A very small percentage of worms was nevertheless able to survive, reach maturity and induce reinfection if given sufficient time to complete their life cycle. Both humoral and local immune responses were associated with worm expulsion.