Specific detection of Histomonas meleagridis in turkeys by a PCR assay with an internal amplification control

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.

Critical Review: Future Control of Blackhead Disease (Histomoniasis) in Poultry

Blackhead disease (histomoniasis) currently has no efficacious drug approved for use in poultry in the United States. Both chickens and turkeys can get the disease, but mortality is most often associated with turkeys. The lack of any approved therapies for blackhead is of concern, especially in the case of valuable turkey breeder candidate flocks. Due to the availability of efficacious drugs for many years, research focused on blackhead was minimal. However, without any drugs or reliable additives, blackhead will continue to be an issue in turkeys and broiler breeder chickens. The American Association of Avian Pathologists annual meeting in San Antonio, Texas, August 6-9, 2016, held a mini-symposium on blackhead. The mini-symposium included university researchers and industry veterinarians discussing blackhead in the United States and Europe including insights on the disease pathogenesis and epidemiology, as well as an update on the current state of blackhead in the United States since the removal of nitarsone from the market in January 2016. This review summarizes the information presented at the mini-symposium and discusses current control measures in an era without efficacious drugs.

Histomonas meleagridis--new insights into an old pathogen

The protozoan flagellate Histomonas meleagridis is the etiological agent of histomonosis, first described in 1893. It is a fastidious disease in turkeys, with pathological lesions in the caeca and liver, sometimes with high mortality. In chickens the disease is less fatal and lesions are often confined to the caeca. The disease was well controlled by applying nitroimidazoles and nitrofurans for therapy or prophylaxis. Since their introduction into the market in the middle of the previous century, research nearly ceased as outbreaks of histomonosis occurred only very rarely. With the ban of these drugs in the last two decades in North America, the European Union and elsewhere, in combination with the changes in animal husbandry, the disease re-emerged. Consequently, research programs were set up in various places focusing on different features of the parasite and the disease. For the first time studies were performed to elucidate the molecular repertoire of the parasite. In addition, research has been started to investigate the parasite's interaction with its host. New diagnostic methods and tools were developed and tested with samples obtained from field outbreaks or experimental infections. Some of these studies aimed to clarify the introduction of the protozoan parasite into a flock and the transmission between birds. Finally, a strong focus was placed on research concentrated on the development of new treatment and prophylactic strategies, urgently needed to combat the disease. This review aims to summarize recent research activities and place them into context with older literature.

Loop-mediated isothermal amplification assay for detection of Histomonas meleagridis infection in chickens targeting the 18S rRNA sequences

Histomonas meleagridis is the causative agent of histomonosis, a disease of gallinaceous fowl characterized by necrotic typhlitis, hepatitis, and high mortality. To develop a rapid and sensitive method for specific detection of H. meleagridis, an assay based on loop-mediated isothermal amplification (LAMP) targeting the 18S rRNA gene was established. The detection limit of the LAMP assay was 10 copies for standard plasmids containing an 18S rRNA gene fragment, which was superior to that of a classical PCR method. Specificity tests revealed that there was no cross-reaction with other protozoa such as Trichomonas gallinae, Blastocytis sp, Tetratrichomonas gallinarum, Plasmodium gallinaceum, Toxoplasma gondii, Eimeria tenella, Leucocytozoon caulleryi and Leucocytozoon sabrazesi. The assay was evaluated for its diagnostic utility using liver and caeca samples collected from suspected field cases, the detection rate was 100 and 97.92%, respectively. These results indicate that the LAMP assay may be a useful tool for rapid detection and identification of H. meleagridis in poultry.

Establishing mono-eukaryotic Histomonas meleagridis cultures from in vivo infection contaminated with Tetratrichomonas gallinarum and Blastocystis spp

SUMMARY The necessity to easily establish Histomonas meleagridis cultures has been underlined extensively by many researchers in order to gain more insights in the biology of H. meleagridis. In addition the occurrence of different protozoa in the caeca of birds impedes, however, the isolation and propagation of H. meleagridis from field outbreaks. Therefore, in a kinetic study using transmission electron microscopy the deleterious effects of adventitious protozoa including Tetratrichomonas gallinarum and Blastocystis spp. on cultured H. meleagridis were examined. To overcome this issue, an easy and successful approach to establish the mono-eukaryotic H. meleagridis culture free of other host's protozoa is proposed. At 10 days post infection, liver lesions of H. meleagridis-infected birds were isolated and inoculated into culture media pre-incubated with caecal bacteria. After 48 h of incubation, presence of H. meleagridis in the cultures was confirmed through morphological evaluation. Additionally, TEM examination and analysis by PCR amplification of the small subunit rRNA gene could exclude the co-cultivation of T. gallinarum and Blastocystis spp. Furthermore, after successful propagation and maintenance of the cultured H. meleagridis, its pathogenicity was affirmed in an infection experiment in turkeys.

Seroprevalence of Histomonas meleagridis in pullets and laying hens determined by ELISA

Serum samples from 1120 layers from 56 flocks and 400 pullets from 20 flocks were tested by an indirect sandwich ELISA to investigate the prevalence of antibodies to Histomonas meleagridis in chickens kept in alternative husbandry systems. The overall prevalence of antibodies to H meleagridis in layers was 37.3 per cent, and positive birds were identified in 50 flocks. This was significantly higher than in pullets, where only 8.3 per cent of the birds tested positive. Optical density (OD) values obtained from pullet sera were much lower than the OD values from layers; however, positive birds were detected in half of the pullet flocks. In particular, all birds from an organic pullet flock were found to be positive, with high OD values. Overall, the highest prevalence of positive sera was obtained from birds kept in free-range flocks. Attempts to reisolate live histomonads from birds in 18 layer flocks were unsuccessful.

Establishing an indirect sandwich enzyme-linked-immunosorbent-assay (ELISA) for the detection of antibodies against Histomonas meleagridis from experimentally infected specific pathogen-free chickens and turkeys

No serological method suitable for large screening of antibodies against Histomonas meleagridis in poultry is available so far, the objective targeted in the present investigation. Consequently, an ELISA was developed as a suitable tool for this purpose. Investigating serum samples from non-infected specific pathogen-free (spf) chickens and commercial turkeys a high-background signal was noticed when ELISA plates were directly coated with purified parasitic cells. This signal was significantly reduced by coating the plates with a polyclonal rabbit antibody, raised against histomonads, prior to the addition of the antigen. Adopting this approach five antigen preparations were compared and a high reproducibility could be demonstrated reflected by a very low coefficient of variation of 5.3% and 1.7% for the chicken and turkey sera, respectively. After this initial development all further experiments were carried out with one set of plates and the same antigen preparation. Investigating chicken sera obtained from birds infected at 14 days of life, OD values above a predetermined cut-off value were observed 2 weeks post-infection and a rise of IgG antibodies was noticed until 6 weeks post-infection, when the experiment was terminated. Non-protected turkeys infected at 6 weeks of age displayed an increasing IgG response until 14 days post-infection, prior to the death of animals due to histomonosis. In comparison, the majority of turkeys vaccinated with attenuated histomonads, obtained through prolonged passaging and challenged 4 weeks later with virulent parasites, displayed a demonstrable antibody response after the challenge only. Antibody titres increased until 4 weeks post-challenge when the birds were killed and the study was terminated. Altogether, the developed indirect sandwich ELISA proved to be a quick and efficient method to detect IgG antibodies against H. meleagridis in sera of experimentally infected chickens and turkeys and will be a helpful tool to obtain more insights into the epidemiology of the parasite and the immune response of its hosts.