Parasitic females of Strongyloides papillosus as a pathogenetic stage for sudden cardiac death in infected lambs

Strongyloidiasis (Strongyloides papillosus) in lambs in Uruguay

Here, we describe a spontaneous outbreak of strongyloidiasis (Strongyloides papillosus) in sheep in Uruguay. In a flock of 150 lambs, 60 animals became ill and 12 died within 3 weeks. Affected animals showed weakness, weight loss, enophthalmos and, in some cases, sudden death. Postmortem examination revealed muscle atrophy, dehydration, and small intestines with a foamy and liquid content. Histological examination of the duodenum and the jejunum showed a thick mucosa with severe villous atrophy, mononuclear mixed infiltrate in the lamina propria, and a large number of nematodes embedded in the mucosa, with numerous granulomas in the lamina propia. Small intestinal content analysis showed a total of 13,200 female nematodes in the duodenum and 2000 in the jejunum, identified as Strongyloides papillosus (Strongyloididae). This parasite has long been considered to behave as a commensal parasite or at least to cause significant disease only when present in large numbers. This report shows that Strongyloides papillosus can be highly pathogenic in sheep.

Strongyloides papillosus causes sudden death in weaned calves on New York dairies

CASE DESCRIPTION

Outbreaks of sudden death in apparently healthy weaned dairy calves due to Strongyloides papillosus parasitism were diagnosed on 2 separate and independent New York (NY) dairies.

CLINICAL FINDINGS

Most calves were found dead; however, 1 calf observed while dying showed signs of tachycardia, tachypnea, vocalization, and convulsions shortly before death. In 6 affected heifers that underwent post-mortem examination, precocious bilaterally symmetric mammary gland enlargement was seen. A portion of their parasitized living cohorts also demonstrated similar mammary gland enlargement. A diagnosis of S papillosus hyperinfection was made based upon the presence of high numbers of S papillosus ova in feces, and confirmation by S papillosus-specific PCR assays. Consistent histopathological findings in affected calves included generalized mammary gland vascular congestion, interstitial edema and hemorrhage with ductal hyperplasia. Mild multifocal cardiomyocyte degeneration was found in 5 of 14 calves examined. Factors believed to contribute to the parasite's environmental amplification and host hyperinfection included group housing on wood shavings and high environmental temperatures and humidity.

TREATMENT AND OUTCOME

Treatment of calves with doramectin pour-on stopped mortality and resolved the udder enlargement.

CLINICAL RELEVANCE

Similar outbreaks have previously been described in Japan and South Bohemia (Czech Republic), where researchers hypothesized that sudden death may be due to fatal arrhythmia caused by a parasite-associated cardiotoxin. This report highlights the importance of including S papillosus among the differential diagnoses for sudden death alone or together with precocious udder enlargement in calves kept in confinement housing.

Zoological institutions as hotspots of gastrointestinal parasites that may affect the success of ungulate reintroduction programmes

BACKGROUND

Ungulates from zoological institutions are frequently used as founders in reintroduction programmes. These animals are subject to specific parasite management as parasitic infections have previously been associated with failed Bovidae reintroductions.

METHODS

Questionnaires to obtain data on how these institutions screen for seasonal parasite presence and the clinical signs they induced in threatened ungulates were sent to 65 institutions involved in European Ex situ Programmes (58.5% response rate). Temperature and relative humidity data were also obtained to categorize each zoological centre.

RESULTS

Strongyloides spp. (52.6%), Trichuris spp. (42.1%), Trichostrongylidae family (39.4%) and Eimeria spp. (36.8%) were the most frequently reported parasites in the received questionnaires. Climatic variables did not influence parasite presence.

CONCLUSION

Our results suggest that artificial microenvironments created by husbandry practices and enclosure design in zoos could create hotspots for gastrointestinal parasites. To maximise the success of reintroduction projects, we recommend that the influence of microclimates on parasite burdens be evaluated.

Gastrointestinal motor disturbance in rabbits experimentally infected with Strongyloides papillosus

Strongyloides papillosus is a common nematode in ruminants, and the rabbit is the only susceptible experimental animal that has been identified to date. It is known that heavy infection with S. papillosus causes death in a number of animals. However, even though a number of fatal cases have been reported, the mechanism by which S. papillosus infection leads to death remains unknown. In this study, the pathogenic effect of S. papillosus infection on gastrointestinal motility in infected rabbits was investigated by radiographic means. Gastrointestinal motility in rabbits experimentally infected with S. papillosus was assessed by contrast radiography after oral administration of barium sulfate on days 11 (group A) and 13 (group B) of infection. Body weight, food intake, fecal weight and egg count per gram of feces (EPG) were examined in order to investigate the effect of infection on gastrointestinal motility. Seven rabbits from each S. papillosus-infected and uninfected group were examined. Significant declines in body weight, daily food intake, and fecal weight, as well as gastrointestinal motor disturbances, were observed in association with elevated EPG counts in infected rabbits. This was only observed during the intestinal phase of S. papillosus infection. These results suggest that gastrointestinal motor disturbances underlie the anorexia, weight loss and subsequent death observed in rabbits infected with adult stage S. papillosus.

The Strongyloides (Nematoda) of sheep and the predominant Strongyloides of cattle form at least two different, genetically isolated populations

Strongyloides sp. (Nematoda) are very wide spread small intestinal parasites of vertebrates that can form a facultative free-living generation. Most authors considered all Strongyloides of farm ruminants to belong to the same species, namely Strongyloides papillosus (Wedl, 1856). Here we show that, at least in southern Germany, the predominant Strongyloides found in cattle and the Strongyloides found in sheep belong to separate, genetically isolated populations. While we did find mixed infections in cattle, one form clearly dominated. This variety, in turn, was never found in sheep, indicating that the two forms have different host preferences. We also present molecular tools for distinguishing the two varieties, and an analysis of their phylogenetic relationship with the human parasite Strongyloides stercoralis and the major laboratory model species Strongyloides ratti. Based on our findings we propose that Strongyloides from sheep and the predominant Strongyloides from cattle should be considered separate species as it had already been proposed by [Brumpt, E., 1921. Recherches sur le determinisme des sexes et de l'evolution des Anguillules parasites (Strongyloides). Comptes rendu hebdomadaires des séances et mémoires de la Société de Biologie et de ses filiales 85, 149-152], but was largely ignored by later authors. For nomenclature, we follow [Brumpt, E., 1921. Recherches sur le determinisme des sexes et de l'evolution des Anguillules parasites (Strongyloides). Comptes rendu hebdomadaires des séances et mémoires de la Société de Biologie et de ses filiales 85, 149-152] and use the name S. papillosus for the Strongyloides of sheep and the name Strongyloides vituli for the predominant Strongyloides of cattle.

The free-living generation of the nematode Strongyloides papillosus undergoes sexual reproduction

The nematode genus Strongyloides consists of parasites that live as parthenogenetic females in the small intestines of their hosts. They can also form a facultative free-living generation with males and females. Recently, research on Strongyloides cellular and molecular biology has concentrated on Strongyloides ratti and Strongyloides stercoralis. We propose that the related nematode Strongyloides papillosus, a common parasite of ruminants, is well suited for comparative and evolutionary studies and we show that it is phylogentically basal to S. ratti and S. stercoralis. Based on cytological observations several reports have proposed that Strongyloides males do not contribute genetically to the next generation, leaving open the question of why males still exist. In contrast, the only study employing molecular markers showed that S. ratti males do pass on genetic material. Here, we demonstrate that in S. papillosus males also contribute molecular genetic markers to the next generation. This is interesting for two reasons. First, it shows that S. papillosus is amenable to genetic analysis and second, it indicates that sexual reproduction is more common in Strongyloides than previously assumed.

Recovery from arrhythmias in lambs infected with Strongyloides papillosus following worm elimination

Calves and lambs heavily infected with Strongyloides papillosus develop cardiac arrest by ventricular fibrillation which is preceded by continuous sinus tachycardia and prolongation of the PQ interval during the patent infection. In the present study, cardiac rhythms following anthelmintic treatment were investigated in lambs infected with S. papillosus to ascertain whether cardiac disorders due to the infection are based on a reversible and curable change. Eight lambs were given a lethal dose of S. papillosus. Five of the animals were injected with ivermectin when they developed continuous sinus tachycardia and prolongation of the PQ interval. The other three animals served as untreated controls. In the treated animals, elevated heart rates and PQ intervals began to decrease between 10 and 21 h, then continuous sinus tachycardia and prolongation of PQ interval disappeared within 39 h of treatment. No arrhythmias were detected after the disappearance of sinus tachycardia. Faecal egg counts became negative within 61 h of treatment. Only a few worms were collected from the small intestine at necropsy. The control animals developed ventricular fibrillation by 349 h after infection, having high faecal egg counts and intestinal worm burdens. These results indicate that cardiac disorders generated by S. papillosus infection are reversible and curable following worm elimination.

Larval somatic antigens effective in inducing an IgG response and protection against Strongyloides papillosus infection

A serum IgG response to Strongyloides papillosus infection was analysed in rabbits. IgG production was induced against 30-200 kDa larval somatic antigens and 21-160 kDa adult excretory/secretory (ES) antigens at 4 weeks postinfection. No immunoreactivity was detected between sera of infected animals and any proteins of larval ES and adult somatic antigens. Protection against larval challenge infection was investigated in rabbits immunized by primary infection and by intradermal inoculations of larval somatic and adult ES antigens. Primarily infected animals had 90% fewer or less worms from day 2 onwards after challenge, and lower faecal egg outputs after challenge, when compared with those in susceptible animals. Immunization with larval somatic antigens induced effective protection, showing 52.6-81.5% reductions in worm recovery from day 5 onwards after challenge, and lower faecal egg outputs after challenge. Systemic immunization with adult ES antigens failed to protect the animals against challenge. The possibility that resistance to S. papillosus reinfection is performed on the killing of migrating larvae in the early stages of infection is discussed. Systemic immune responses to larval somatic antigens might play an important role in the resistance.