HEPATIC CALODIUM HEPATICUM (NEMATODA) INFECTION IN A ZOO COLONY OF BLACK-TAILED PRAIRIE DOGS (CYNOMYS LUDOVICIANUS)

Canine hepatic calodiosis with cirrhosis

The nematode parasite Calodium hepaticum (Capillaria hepatica) has a global distribution and is commonly reported in rodents (definitive host), dogs, cats and wild animals. Humans especially children are more susceptible to the parasitic infection. This paper documents an incidental finding of hepatic calodiosis with cirrhosis in a stray dog and discusses the zoonotic implications. A non descript dog was brought for necropsy examination to the Department of Veterinary Pathology, Madras Veterinary College, Tamil Nadu, India. Liver appeared dark brown, mottled with multifocal random variably sized, grey white flat firm areas. Histopathologically, liver tissue revealed multiple random encysted large collection of eggs surrounded by mild inflammation with a few lymphocytes, macrophages and fine fibrosis. The eggs had characteristic barrel shape, bipolar ends, bilayered wall, cross striations between the walls, and yolk. Periodic acid Schiff stain demonstrated the glycolic wall of ova. Marked portal to portal fibrosis was demonstrated by Masson's trichrome (for collagen) and by Warthin-Starry (for reticulin) stains. The stage of parasitic infection was diagnosed as intermediate to chronic due to fibrosis. A need to study the prevalence of the disease in rodents, human and animals is emphasized. Improper burial of carcasses of rodents and dogs may contribute to spread of infection. Pets and stray animals may transmit infection to human and pose health risk.

A scoping review of rodent-borne pathogen presence, exposure, and transmission at zoological institutions

BACKGROUND

Rodents are one of the major taxa most likely to carry zoonotic diseases, harboring more than 85 unique zoonotic pathogens. While the significance of rodents' capacity to carry and transmit disease has been characterized in urban settings, the zoo environment is particularly unique given the overlap of collection, free-living, and feeder rodents as well as non-rodent collection animals, staff, and visitors.

ELIGIBILITY CRITERIA

This scoping review examines reports of rodent-borne pathogen detection or transmission in zoo settings extracted from the literature. Papers were included in the final analysis if there was evidence of presence or exposure to a pathogen in a rodent at a zoological institution.

SOURCES OF EVIDENCE

Publications were included from PubMed, CAB Abstracts and Biological Abstracts searched in August 2019.

CHARTING METHODS

Data extracted from publications on pathogen presence/exposure included publication identifiers, study identifiers, infectious agent identifiers, rodent identifiers, and non-rodent collection animal identifiers. Extraction from papers with evidence of disease transmission included number of rodents involved in transmission, non-rodent collection animal species and numbers, and job title of humans involved, diagnostic tests performed, and clinical outcomes.

RESULTS

Aggregate literature examined included 207 publications presenting evidence of pathogen presence and/or exposure in rodents across 43 countries in over 140 zoological institutions. A total of 143 infectious agent genera were identified, comprising 14 viral genera, 31 bacterial genera, 83 parasitic genera, and 15 fungal genera. Of these infectious agents, over 75 % were potentially zoonotic. The most common disease-causing agent genera identified were Leptospira, Toxoplasma, Salmonella, and Yersinia. Additional screening for evidence of pathogen transmission across species yielded 30 publications, indicating an area for future investigation to better inform surveillance and management priorities in order to reduce exposure, infection, and transmission.

CONCLUSIONS

Analyzing the breadth of rodent species and pathogens identified at zoos highlights the unique opportunity zoos have to be at the forefront of the early detection and identification of novel hosts and geographic ranges of rodent-borne pathogens with high impact on both endangered species and people. The overlap of these populations at zoos exemplifies the importance of considering One Health when prioritizing surveillance and risk mitigation of rodent reservoirs at zoos.

Identification of Giardia duodenalis and Enterocytozoon bieneusi in an epizoological investigation of a laboratory colony of prairie dogs, Cynomys ludovicianus

Since 2005, black-tailed prairie dogs (Cynomys ludovicianus) have been collected for use as research animals from field sites in Kansas, Colorado, and Texas. In January of 2012, Giardia trophozoites were identified by histology, thin-section electron microscopy, and immunofluorescent staining in the lumen of the small intestine and colon of a prairie dog euthanized because of extreme weight loss. With giardiasis suspected as the cause of weight loss, a survey of Giardia duodenalis in the laboratory colony of prairie dogs was initiated. Direct immunofluorescent testing of feces revealed active shedding of Giardia cysts in 40% (n=60) of animals held in the vivarium. All tested fecal samples (n=29) from animals in another holding facility where the index case originated were PCR positive for G. duodenalis with assemblages A and B identified from sequencing triosephosphate isomerase (tpi), glutamate dehydrogenase (gdh), and β-giardin (bg) genes. Both assemblages are considered zoonotic, thus the parasites in prairie dogs are potential human pathogens and indicate prairie dogs as a possible wildlife reservoir or the victims of pathogen spill-over. Molecular testing for other protozoan gastrointestinal parasites revealed no Cryptosporidium infections but identified a host-adapted Enterocytozoon bieneusi genotype group.

An overview of the host spectrum and distribution of Calodium hepaticum (syn. Capillaria hepatica): part 2-Mammalia (excluding Muroidea)

Calodium hepaticum (syn. Capillaria hepatica) is a globally distributed zoonotic nematode with low host specificity and a high affinity to the liver. Although murid rodents are the main definite hosts, various other mammals can be affected with hepatic capillariasis: non-murid rodents, Insectivora, Chiroptera, Lagomorpha, Artiodactyla, Perissodactyla, Hyracoidea, Marsupialia, Carnivora, and Primates. Overall, more than 180 mammalian species (including humans) are known as suitable hosts of this pathogen. This review gives an overview of the distribution and host spectrum of C. hepaticum in non-Muroidean mammals in wildlife and zoos as well as in domesticated and laboratory animals. Furthermore, the role of spurious infections in animals and the dissemination of C. hepaticum by mammalian and non-mammalian animals are summarized.

Prevalence of Calodium hepaticum (Syn. Capillaria hepatica) in house mice (Mus musculus) in the Azores archipelago

Calodium hepaticum (Syn. Capillaria hepatica) is a zoonotic liver nematode of mammals distributed worldwide. Rodents are believed to be the main reservoirs of this nematode. In this paper, prevalence of the parasite was analyzed in liver histological sections from 51 house mice (Mus musculus) caught in human-inhabited houses, from two localities (Furnas and Rabo de Peixe) on São Miguel island from the Azores archipelago (Portugal). Mean prevalence of infection was 19.6%, with 33.3% prevalence in Furnas and 4.1% in Rabo de Peixe (P=0.07). No significant differences were found between the prevalence of infection and the age, body weight and the sex of mice. Hepatic lesions found were either acute and/or chronic stage and consisted of moderate to severe multifocal pyogranulomatous hepatitis with encapsulated eggs with typical bipolar plugs and moderate to severe necrotizing hepatitis consistent with larva tracks. Periportal inflammatory infiltration, hepatocyte regeneration and bile duct hyperplasia were also noted. In most cases, hepatic lesions occupied more than 50% of the liver, but despite severe lesions, in some mice, no signs of hepatic failure were noticed. The high rate of infection found in the present study suggests that house mice are an important reservoir for this parasite in the Azores and could have a role in human transmission.

Fatal toxoplasmosis and concurrent Calodium hepaticum infection in Korean squirrels (Tanias sibericus)

Four Korean squirrels (Tanias siberius) imported in Spain from People's Republic of China died 2 days after their arrival at a pet shop. They had neurological signs associated with generalized toxoplasmosis involving brain, lungs, liver, and the heart. Toxoplasma gondii-like tachyzoites and tissue cysts were found in organs of all four squirrels. The protozoa stained positively with T. gondii polyclonal antibodies and were ultrastructurally similar to T. gondii. Calodium (Capillaria) hepaticum infection was found in the liver of one squirrel.

Calodium hepaticum (syn. Capillaria hepatica) in captive rodents in a zoological garden

Calodium hepaticum infection was diagnosed in the Bristol Zoo Gardens in 13 captive rodents of four species that died or were humanely killed over a 40-month period. Of these infected animals, nine were black-tailed prairie dogs (Cynomus ludovicianus), representing 45% of the members of this species examined during the study. A wild rat (Rattus norvegicus) found dead in an enclosure was also infected. To date few cases of C. hepaticum infection have been reported in the UK. The number of cases diagnosed in this urban zoo may be explained by the potentially high prevalence of infection in urban rat populations and increased risk of exposure of zoo animals kept in enclosures to which rats have access. As C. hepaticum is potentially zoonotic, members of staff in zoos should be careful to avoid soil-to-mouth contact, particularly in prairie dog enclosures.