Heterakis gallinarum, the Cecal Nematode of Gallinaceous Birds: A Critical Review

First molecular insights into gastrointestinal helminths of domestic birds in the Caspian Sea Littoral of Iran with an emphasis on the One Health concern

The current investigation was carried out during the period from July 2022 to March 2023, aiming to investigate the prevalence of gastrointestinal helminths in domestic birds collected from traditional markets in Guilan province. One hundred forty-eight domestic birds, including chickens (Gallus gallus domesticus), domestic ducks (Anas platyrhynchos domesticus), greylag geese (Anser anser), and domestic turkeys (Meleagris gallopavo domesticus) were examined. Totally, 42.56% of the investigated birds were positive for helminthic parasites. Morphological analysis revealed varying infection rates among birds: Echinostoma revolutum (5.40%), Hypoderaeum conoideum (2.02%), Cloacotaenia megalops (0.67%), Hymenolepididae family (4.05%), Ascaridia galli (16.89%), and Heterakis gallinarum (4.72%). The investigation involved molecular analysis of the 18S and ITS1 + 5.8S + ITS2 rRNA gene regions. The findings indicated that the 18S region of nematode isolates exhibited a similarity of 92 to 100% with sequences in the GenBank, whereas trematode and cestode isolates showed a gene similarity ranging from 88 to 99%. The ITS regions of nematode, trematode, and cestode isolates exhibited genetic similarities ranging from 87 to 100%, 73-99%, and 75-99%, respectively. Furthermore, phylogenetic analysis confirmed the categorization of the identified species within the Ascaridiidae, Heterakidae, Hymenolepididae, and Echinostomatidae families, indicating their close affinity with previously documented species. Implementing precise control measures such as consistent monitoring, adequate sanitation protocols, and administering anthelmintic treatments is crucial for effectively managing parasitic infections in free-range and backyard poultry farms. Additionally, conducting further surveys is advisable to assess the impact of these parasites on the health and productivity of poultry in the investigated area.

Diversity of fecal parasitomes of wild carnivores inhabiting Korea, including zoonotic parasites and parasites of their prey animals, as revealed by 18S rRNA gene sequencing

Consisting of diverse groups of organisms, parasites are among the least studied pathogens despite their enormous impacts on humans, livestock, and wildlife. In particular, little is known about their host specificity and diversity in wildlife. Here, using multiple primer pairs and sequencing 18S rRNA genes of diverse groups of parasites, we aimed to investigate fecal parasitomes of carnivorous wildlife in Korea, namely, the raccoon dog (Nyctereutes procyonoides), the leopard cat (Prionailurus bengalensis), and the Eurasian otter (Lutra lutra). A total of 5 host-specific parasite species were identified, including 2 from raccoon dogs, 2 from leopard cats, and 1 from Eurasian otters. In addition, numerous parasite species of their prey animals were detected in their feces. It was found that the parasitome composition varied between host animals, and it was thought that the difference was attributed to the difference in prey animals, as numerous small mammal parasites were detected from feces of leopard cats inhabiting inland areas and fish parasites from feces of Eurasian otters and raccoon dogs inhabiting waterside areas. Furthermore, 5 zoonotic parasites known to infect humans were identified at the species level. Wildlife-associated zoonoses are expected to increase as the proximity between humans and wildlife increases due to urbanization. Vigilance may be necessary, such as by monitoring parasites in wildlife feces, as was done in this study.

Cancerogenic parasites in veterinary medicine: a narrative literature review

Parasite infection is one of the many environmental factors that can significantly contribute to carcinogenesis and is already known to be associated with a variety of malignancies in both human and veterinary medicine. However, the actual number of cancerogenic parasites and their relationship to tumor development is far from being fully understood, especially in veterinary medicine. Thus, the aim of this review is to investigate parasite-related cancers in domestic and wild animals and their burden in veterinary oncology. Spontaneous neoplasia with ascertained or putative parasite etiology in domestic and wild animals will be reviewed, and the multifarious mechanisms of protozoan and metazoan cancer induction will be discussed.

Prevalence and magnitude of gastrointestinal helminth infections in cage-free laying chickens in Australia

Helminth infections have been re-emerging with the growing popularity of free-range and floor-based chicken production systems. The aim of this study was to determine the prevalence and worm burdens of intestinal helminth infection in cage-free laying chickens in Australia. In an online survey about worm prevalence, a high proportion of respondents reported the detection of Ascaridia galli (77%), followed by tapeworms (69%) and caecal worms (Heterakis gallinarum) (62%), whereas fewer respondents (23%) reported the presence of hair worms (Capillaria spp.) in their flocks. Total worm recovery from 407 laying hens on four farms found that 92.1% of hens harboured one or more helminth parasite with a prevalence of 73 to 100% across farms. Mixed infections were common with 79% of hens harbouring two or more helminth species. The prevalence of nematode species H. gallinarum, A. galli and Capillaria spp. was 87, 82 and 35% respectively. Five cestode species were found with a low individual chicken prevalence (Raillietina tetragona 4.7%, Raillietina echinobothrida 3.2%, Raillietina cesticillus 5.2%, Choanotaenia infundibulum 4.4%, and Hymenolepis cantaniana 4.4%). The hens harboured an average of 71 worms with H. gallinarum having the highest mean burden (45.5 worms/hen) followed by A. galli (22.0 worms/hen), Capillaria spp. (2.7 worms/hen) and cestodes (0.8 worms/hen). The sex ratio (female:male worms) was 1.38:1 for A. galli, and 1.77:1 for H. gallinarum. There was a strong positive correlation between A. galli female worm count and excreta egg count (EECs) (r_s = 0.94, P < 0.0001) and also between total nematode worm count and EEC (r_s = 0.82, P < 0.0001) in individual hens. When investigating intestinal excreta (n = 10) and caecal excreta (n = 10) of 16 chicken flocks the prevalence of infection with ascarid worms in intestinal and caecal excreta was 71 and 78% respectively and 27% prevalence of Capillaria spp. in intestinal excreta with mean EECs of 407, 404, and 18 eggs/g of excreta (EPG), respectively. These results suggest that most chickens kept in free-range or floor production systems are infected with one or more helminth parasite species. Heavy worm infections would likely affect the production performance and welfare of birds with adverse economic impact. Strategic or tactical anthelmintic treatment with effective anthelmintic could reduce this impact.

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.

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.

In addition to birds' age and outdoor access, the detection method is of high importance to determine the prevalence of gastrointestinal helminths in laying hens kept in alternative husbandry systems

The prevalence of gastrointestinal helminths was investigated in sixty-six commercial non-caged layer flocks. Twenty-nine flocks were housed indoors in aviaries or floor systems, nineteen flocks were kept in conventional free-range systems with outdoor access, and eighteen flocks in organic free-range systems. Flocks were investigated at end of rearing (mean age 17 weeks), peak of egg production (mean age 38 weeks) and before slaughter (mean age 74 weeks). Four different methods were applied to determine worm infestation. During necropsies, worm infestations were recorded and mucosal scrapings were evaluated for the presence of worm eggs. Faecal samples from each flock were investigated by simple flotation method and McMaster counting technique. No gastrointestinal helminths were found in pullets. During production, 87.9 % of the layer flocks were infected with at least one nematode species at the peak of production. The prevalence further increased significantly up to 98.5 % at the end of production (p=0.05). This increase could be ascribed mainly to infections with Ascaridia (A.) galli and/or Heterakis (H.) gallinarum which were most prevalent in all husbandry systems. Furthermore, their prevalence increased significantly with the age of birds (p=0.023; p < 0.001). With regard to the husbandry system, the prevalence of Capillaria spp. was significantly higher in flocks from outdoor systems compared to flocks that were kept indoors. Cestodes were only detected at the end of production with a prevalence of 15.2 % and significantly more flocks with access to outdoor run were found positive. Interestingly, H. gallinarum was found with a high prevalence indoor and in outdoor systems. Anthelminthic treatment did not impact the prevalence of nematode infections. Comparing four different methods for the detection of helminths it was revealed that their efficiencies varied depending on the worm species. Overall, the simple flotation method was superior to detect A. galli and Capillaria spp. This method proved also very efficient for the detection of H. gallinarum but the additional evaluation of the worm infestation during necropsy increased the level of prevalence. Cestodes were mainly found during necropsies when the worm infestation was evaluated. The detection of parasite eggs in mucosal scrapings from the intestines was the least effective method for all helminths. These findings lead to the recommendation to combine faecal investigations with an evaluation of the worm infestation during necropsy of at least five birds.

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.

Development of a multiplex PCR method for discriminating between Heterakis gallinarum, H. beramporia, and H. indica parasites of poultry

Heterakis gallinarum, H. beramporia, and H. indica are common nematodes in gallinaceous poultry in Asian countries, and the infections occasionally lead to declining health of the hosts. These three Heterakis spp. can be identified by the morphological characteristics of the male worms; however, the female worms and eggs cannot be identified because they have no reliable morphological characteristics for discrimination. In addition, H. gallinarum is a well-known vector of fetal protozoan Histomonas meleagridis, making the discrimination between these three Heterakis species important in basic and clinical veterinary parasitology. We analyzed nuclear ribosomal 18S-ITS1-5.8S-ITS2-28S DNA sequences of these three Heterakis species. The 18S, 5.8S, and 28S DNA sequences had very high homology between the species; however, the ITS1 and ITS2 sequence similarity was 68.5 %-93.2 %. H. gallinarum, H. beramporia, and H. indica were divided into separate clades in the ITS1 and ITS2-concatenated phylogenetic tree. Therefore, to develop a multiplex PCR method for discriminating between the three Heterakis species, we designed species-specific reverse primers within the ITS2 region as follows: H. gallinarum-specific HgI2-R, H. beramporia-specific HbI2-R5, and H. indica-specific HiI2-R. The multiplex PCR amplified 396-bp, 272-bp, and 482-bp fragments specific to H. gallinarum, H. beramporia, and H. indica DNA, respectively, and did not amplify the fragments using other chicken nematode DNAs such as Ascaridia galli, Oxyspirura mansoni, Dispharynx nasuta, and Cheilospirura hamulosa. These results suggest that the multiplex PCR would serve as a useful tool for identifying and diagnosing infections of H. gallinarum, H. beramporia, and H. indica in poultry.

Molecular characterization of Ascaridia galli from Bangladesh and development of a PCR method for distinguishing A. galli from Heterakis spp

We analyzed the nuclear ribosomal internal transcribed spacer (ITS) 1 and ITS2 sequences for Bangladesh isolates of Ascaridia galli, and we determined that the sequences were unreliable as molecular markers for distinguishing A. galli from other Ascaridia species, because the sequences showed high identity with that of A. columbae. However, the ITS1 sequences were available for designing PCR primers distinguishable between Ascaridia galli and Heterakis spp. Bangladesh isolates of A. galli constituted a monophyletic clade along with other geographical isolates in the cytochrome c oxidase subunit I (COI) phylogenetic tree, however, we could not clarify the phylogenetic relationships between A. galli and other Ascaridia spp., because their available sequences in GenBank were very few. The developed PCR method using DNA from A. galli and Heterakis spp. eggs would enable differential diagnosis of the individual infections in the future.