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Cryptosporidium parvum is not transmissible to fish, amphibians, or reptiles
T K Graczyk1, R Fayer, M R Cranfield
1Department of Molecular Microbiology and Immunology, School of Hygiene and Public Health, Johns Hopkins University, Baltimore, Maryland 21205, USA.
Abstract:
A recent report suggested that an isolate of Cryptosporidium parvum had established infections in fish, amphibians, and reptiles and raises concern that animals other than mammals might be a potential source of waterborne Cryptosporidium oocysts. To test this possibility, viable C. parvum oocysts, infectious for neonatal BALB/c mice, were delivered by gastric intubation to bluegill sunfish, poison-dart frogs, African clawed frogs, bearded dragon lizards, and corn snakes. Histological sections of the stomach, jejunum, ileum, and cloaca prepared from tissues collected on days 7 and 14 postinoculation (PI) were negative for Cryptosporidium developmental stages. However, inoculum-derived oocysts were detectable by fluorescein-labeled monoclonal antibody in feces of inoculated animals from day 1 to day 12 PI in fish and frogs, and up to day 14 PI in lizards. Snakes did not defecate for 14 days PI. Impression smears taken at necropsy on days 7 and 14 PI revealed C. parvum oocysts in the lumen of the cloaca of 2 fish and 1 lizard on day 7 PI only. Because tissue stages of the pathogen were not found, it appears that C. parvum was not heterologously transmitted to lower vertebrates. Under certain circumstances, however, such as after the ingestion of C. parvum-infected prey, lower vertebrates may disseminate C. parvum oocysts in the environment.
Insights
Lower vertebrates like fish, amphibians, and reptiles do not appear to be a significant source of Cryptosporidium parvum oocysts. However, they may still spread these waterborne parasites under certain conditions.
Area of Science:
- Veterinary Parasitology
- Environmental Health
- Infectious Diseases
Background:
- Cryptosporidium parvum is a significant cause of waterborne disease.
- Previous reports suggest potential infection in non-mammalian hosts, raising concerns about environmental contamination.
- The role of lower vertebrates as reservoirs for C. parvum remains unclear.
Purpose of the Study:
- To investigate the potential for Cryptosporidium parvum infection and oocyst shedding in fish, amphibians, and reptiles.
- To determine if these animals can serve as a source of waterborne C. parvum oocysts.
- To assess the risk of heterologous transmission of C. parvum to lower vertebrates.
Main Methods:
- Viable, infectious C. parvum oocysts were administered via gastric intubation to bluegill sunfish, poison-dart frogs, African clawed frogs, bearded dragon lizards, and corn snakes.
- Animals were necropsied on days 7 and 14 postinoculation (PI).
- Histological examination of gastrointestinal tissues and detection of oocysts in feces and cloacal smears were performed.
Main Results:
- No Cryptosporidium developmental stages were found in histological sections of any inoculated animals.
- Inoculum-derived oocysts were detected in the feces of fish and frogs (days 1-12 PI) and lizards (up to day 14 PI).
- Oocysts were found in the cloacal lumen of one fish and one lizard on day 7 PI.
Conclusions:
- Cryptosporidium parvum does not appear to undergo heterologous transmission and development in fish, amphibians, or reptiles.
- Lower vertebrates can excrete viable C. parvum oocysts, potentially disseminating them into the environment.
- These animals may act as indirect disseminators of C. parvum, particularly if they ingest infected prey.