The Identification of Haemonchus Species and Diagnosis of Haemonchosis

Characterization and population genetics of Haemonchus contortus in Merino sheep in Lesotho

Haemonchus contortus is the most pathogenic and economically restrictive gastrointestinal nematode in the small ruminant industry globally. Morbidity, poor cross-bodily state, and mortality of sheep in Lesotho suggest the presence of H. contortus. The present study investigated the morphological, molecular, and population genetics of H. contortus third-stage larvae infecting sheep in four ecological zones (EZ) of Lesotho. Coprocultures were prepared for larval morphological identification and PCR determination. Larvae were identified morphologically as 100% H. contortus. The Second Internal Transcribed Spacer (ITS-2) gene of the ribosomal DNA of H. contortus isolates in the present study revealed nucleotide homology ranging from 97 to 100% when compared with selected GenBank reference sequences. Pairwise evolutionary divergence among H. contortus isolates was low, with 0.01318 recorded as the highest in the present study. Five haplotypes resulted from 14 Lesotho sequences. Haplotype diversity and nucleotide diversity were 0.76923 and 0.00590, respectively. Genetic differentiation among isolates was low but not statistically significant. An analysis of molecular variance revealed that most molecular variation was distributed within topographic populations at 94.79% (FST = 0.05206, p > 0.05) and 5.21% among populations. There was high gene flow and no definite population genetic structure among Lesotho isolates.

Epidemiological, Morphological, and Morphometric Study on Haemonchus spp. Recovered From Goats in Egypt

Goats can be infected by multiple groups of external and internal parasites. Haemonchus spp. are among abomasal parasites that can result in higher mortality and several considerable economic losses in goats. Early detection of parasites and better understanding of the major risk factors associated with infection are among the main strategies for controlling the infection. Considering this, information on hemonchosis in goats from Egypt, and the contribution of goats in the maintenance of the epidemiological foci of the disease is limited. This study investigated the prevalence of Haemonchus species among 240 abomasum samples collected during postmortem examination of goat carcasses from Assiut Governorate, Egypt. Moreover, the association of the major risk factors to describe the epidemiological pattern of the disease was explored. This study demonstrated that 16.66% of abomasa samples harbored Haemonchus species. Additionally, age, sex, and sampling season were the most significant risk factors associated with infection. Following the variable factors under study, goats aged 1 year or older were at higher risk, with an infection rate of 22.14% (31 of 140), than those younger than 1 year (9%) [p = 0.008; odds ratio (OR) = 2.87; 95% confidence interval (CI), 1.30-6.35]. The infection rate was 25% (19 of 76) in males and 12.8% (21 of 164) in females [p = 0.024; odds ratio (OR) = 2.26; 95% confidence interval (CI), 1.13-4.53]. Moreover, the exposure to infection was higher in summer (22.22%) than in winter (8.33%) (p = 0.007; odds ratio (OR) = 0.318; 95% confidence interval (CI), 0.139-0.725). More importantly, three species of the parasite-Haemonchus contortus, Haemonchus placei, and Haemonchus longistipes-were identified for the first time, and the confirmation of the identification and morphological characterization of the worms was performed using light microscopy and SEM. Collectively, this study reveals interesting epidemiological, morphological, and morphometric findings associated with the occurrence of hemonchosis among goats in Egypt. This study suggests further research for exploring the major circulating species of the parasite in Egypt, which is mandatory for controlling the disease.

Triple lectin staining of trichostrongyle eggs from naturally infected small ruminants

Trichostrongyle nematodes can be a major threat to the profitability of small ruminant producers depending of the species and intensity of trichostrongyles parasitizing their herd. Haemonchus contortus, Teladorsagia circumcincta, and Trichostrongylus colubriformis are typically the most common and clinically important species. Three lectins (PNA, LCA and AAL) have been reported to bind specifically to eggs from these three genera and therefore could be used to quantify the intensity of each species in individual animals. Peanut agglutinin (PNA) has been the most commonly tested lectin because it selectively binds intensely to eggs of the most pathogenic species, H. contortus. Lens culinaris agglutinin (LCA) and Aleuria aurantia agglutinin (AAL) have shown specificity to T. circumcincta and Trichostrongylus spp. respectively, however, these lectins have only been evaluated using eggs harvested directly from adult females, and not from fecal samples. The purpose of the present study is to describe a method to sequentially stain H. contortus, T. circumcincta and Trichostrongylus spp. fecal eggs with PNA, LCA and AAL, and then evaluate the resultant staining patterns seen with eggs collected from a naturally infected goat shown with PCR to contain H. contortus, T. circumcincta, Ostertagia leptospicularis, Trichostrongylus colubriformis and Trichostrongylus axei eggs. These results were also compared with patterns observed with eggs stained with single lectins and double combinations of lectins. The various patterns were then compared to those seen with egg samples collected from an ewe shown to only contain H. contortus. PNA bound intensely and uniformly to all eggs from samples containing only H. contortus eggs; however, some eggs additionally bound LCA and AAL in localized patches of varying size, and a few eggs exhibited intense and uniform binding of all three lectins. Single PNA-staining of goat samples containing the five trichostrongyles species identified most eggs as H. contortus, and triple-staining showed patterns consistent with those seen for H. contortus. Binding of AAL to non-Haemonchus eggs was uniform but showed significant variations in intensity. Lesser staining eggs tended to also stain intensely with LCA, which is consistent with published binding pattern for T. circumcincta. Most eggs that AAL bound intensely to did not bind with LCA, which is consistent with published binding pattern for Trichostrongylus spp. Autofluorescence was observed with the DAPI filter-cube among most non-Haemonchus eggs. This study demonstrates the need for additional field studies to further validate the specificity of these three lectins for use in identifying eggs from the three species of trichostrongyles.

Ovine haemonchosis: a review

Sheep farming is the backbone of a rural economy in developing countries, and haemonchosis is a major impediment in the way of its progress. Haemonchus contortus (H. contortus) infection persists all over the world particularly in the tropical and sub-tropical regions. Various review articles have been published to substantially cover one or more aspects of its morphology, prevalence, pathogenesis, symptoms, diagnosis, immune response, drug resistance, treatment, and control measure. The objective of this paper is to briefly review past and present information available in the aforementioned areas in one place to enable the readers to fully understand the problem from a broader perspective. H. contortus parasite harbours in abomasum of affected animal and feeds on its blood, producing mild to severe symptoms and even death in acute form. The parasite thus inflicts heavy production losses and is of economic importance. H. contortus has developed diverse characters over the years leading to limited success in the production of vaccines. Indiscriminate use of the anthelmintics has produced drug resistance against almost all conventional products. Efficacy of medicinal plants and non-conventional chemicals has been reported under controlled experiments; however, research on their adverse effects on growth and fertility is yet to be studied. Research on molecular tools for identification and introduction of resistant genes into the flock is also underway but still a long journey to find its field application. Crossbreeding may compromise the production traits of the existing flock. In given circumstances, a targeted selective treatment approach along with selective breeding, culling of more susceptible animals, and maintaining a good body condition score through the provision of a balanced diet remains a workable strategy to control haemonchosis in sheep.

Development of SYBR Green real-time PCR for diagnosis of fasciolosis in sheep

Fasciolosis is commonly diagnosed by microscopic detection of egg following sedimentation. However, this technique is time-consuming when a large number of samples must be processed and requires sufficient experience. Quantitative real-time PCR based on the detection of liver fluke ribosomal DNA in feces has been introduced, which is more accurate and liable to reflect the presence of flukes in hosts. This study aimed to develop an efficient molecular detection method in laboratory diagnosis. A cross-sectional study of 250 sheep was performed to detect Fasciola hepatica infections using gold standard microscopic detection, conventional PCR and real-time PCR. Both conventional and real-time PCRs targeted the internal transcribed spacer 2 (ITS-2). A composite reference standard(CRS) was used to analyze the sensitivity and specificity of three methods. Furthermore, the minimal amount of plasmid DNA detected by the real-time PCR was 1.67 pg plasmid DNA (equivalent to 1.1 × 10⁶ copies). In conclusion, a highly sensitive and specific method for fasciolosis in sheep was developed.

Droplet digital polymerase chain reaction (ddPCR) as a novel method for absolute quantification of major gastrointestinal nematodes in sheep

In this paper, we present for the first time a new tool, based on Droplet Digital™ Polymerase Chain Reaction (ddPCR), for absolute quantification of key genera of gastrointestinal (GI) nematode parasites of grazing livestock. Four combinations of primers/probe sets targeting the internal transcribed spacer region 2 (ITS2) of the ribosomal RNA gene array were designed using the Primer3 software, following in silico analysis of nucleotide sequences from nematodes of interest downloaded from common databases. The amplified regions include both a universal region for detection of any strongylid gastrointestinal parasite and three different genus specific regions, making it possible to differentiate between the most important GI nematodes of sheep in Sweden: Haemonchus, Teladorsagia and Trichostrongylus. Analysis of samples containing serial dilutions and different mixtures of genomic DNA extracted from different species of adult worms proved useful in assessment of different threshold settings with the QuantaSoft software. Analysis of template DNA from these worms indicated that ddPCR is a viable choice for detection and absolute quantification of the different genera and also in samples with multiple species. Interpretation of the ddPCR results was straightforward and choice of analytical approach had little influence on the final results. Thus, the results obtained in the different analytical approaches seemed to be robust and the concentrations determined were uniform. Furthermore, the linear range of the Haemonchus ddPCR assay was similar to that of real-time PCR (qPCR). Taken together, our data confirm the suitability of ddPCR for detection and absolute quantification of three major sheep pathogens when tested on larval cultures from pooled ovine faeces. The results also indicate that ddPCR can be a useful complement to applications based on conventional egg counting methods such as the faecal egg reduction test (FECRT).

Comparison of Four Diagnostic Methods for Detection and Relative Quantification of Haemonchus contortus Eggs in Feces Samples

We compared four methods for identification of Haemonchus contortus eggs. With increased trade in animals within and between countries and continents, it has become important to correctly identify H. contortus eggs in fecal samples. To validate the outcome of diagnostic tests, sheep feces (n = 38) were collected from naturally infected flocks in Sweden. Subsamples were analyzed with (a) McMaster egg counting; (b) differential counting of eggs after staining with peanut agglutinin (PNA); (c) detection of DNA following amplification by real-time quantitative polymerase chain reaction (qPCR); and (d) loop-mediated isothermal amplification (LAMP). Differences between similar tests (microscopic and molecular) and SD (±SD) were analyzed with Bland-Altman plots and Spearman rank correlation. Strongylid egg counts ranged from 200 to 12,100 eggs per gram (epg) (mean epg ± SD = 1,278 ± 2,049). Microscopy showed presence of H. contortus eggs in 27 (73%) unstained samples and in 28 (76%) samples stained with PNA, whereas 29 samples (78%) tested positive in LAMP and 34 (91%) in qPCR analysis. The cycle threshold (Ct) values with LAMP ranged between 13 and 38 (mean ± SD = 21 ± 7), and those in qPCR between 25 and 49 (mean ± SD = 33 ± 6). In the LAMP and qPCR analyses, seven (19%) and three (8%) samples, respectively, had a cycle threshold (Ct) >35, whereas no reactions were observed in eight (22%) and three (8%) samples, respectively. There was good agreement between the diagnostic tests based on microscopic examination and DNA detection, although the molecular tests were more sensitive. The bias between the microscopy methods (-4.2 ± 11) was smaller than for the molecular tests (-9.8 ± 10). The observed ranking in terms of test sensitivity was: McMaster counting by conventional microscopy < PNA < LAMP < qPCR. In conclusion, H. contortus can be identified by McMaster counting, without major mistakes regarding false positive results. However, molecular methods provide the capacity to diagnose H. contortus eggs with increased accuracy. This is essential when animals are investigated in quarantine or in studies evaluating anthelmintic treatment efficacy. These methods could also be applied to fecal samples from wildlife to investigate nematode transmission between wildlife and livestock.