Cryptosporidiosis is caused by Cryptosporidium spp, ubiquitous protozoal organisms that persist in the environment for variable periods depending on temperature and humidity. Infection leads to respiratory and GI disease in birds. Diagnosis is by fecal float or microscopic examination of tissues. No known effective treatments for cryptosporidiosis exist; good biosecurity and sanitation are the most important steps to minimize transmission.
Cryptosporidiosis in poultry is economically important and has been reported in various wild and captive species, including domesticated chickens, turkeys, ducks, geese, quails, pheasants, and peacocks. Cryptosporidiosis is more severe in turkeys than in chickens and is frequently fatal in quail.
Etiology and Pathogenesis of Cryptosporidiosis in Poultry
Cryptosporidiosis is caused by protozoa (phylum Apicomplexa) that are members of the family Cryptosporidiidae and are related to, but distinct from, coccidia of the genera Eimeria, Isospora, Sarcocystis, and Toxoplasma.
Originally, it was thought that there were 19 species in the genus Cryptosporidium; however,research has shown that most are merely species that lack host specificity or host recognition, and now over 40 species are recognized (1, 2, 3). In poultry at least 3 species have been identified, including C baileyi in chickens, turkeys, and ducks; C meleagridis in turkeys and chickens; and C galli in chickens.
Cryptosporidia are parasitic in the intestine of mammals; however, in birds they are commonly found in the cloacal bursa (bursa of Fabricius) and in the respiratory tract. In turkeys and chickens, Cryptosporidia have been found in the sinuses, trachea, bronchi, cloaca, and bursa.
The life cycle of Cryptosporidium involves multiple asexual phases and one sexual phase within the epithelial cells, culminating in oocyst production. Each cycle leads to destruction of the parasitized cells, which leads to the clinical signs.
In the host, the oocyst forms four sporozoites without sporocysts. The life cycle is not self-limiting, because some oocysts are thin-walled and release sporozoites (after trypsin/bile stimulation) that reinfect adjacent tissues. The endogenous cycle is short (4–7 days), the endogenous stages are small (4–7 mcm in diameter), and the parasites are just beneath the epithelial cell membranes (see image of cryptosporidiosis infection in turkey). The oocysts are excreted sporulated and are immediately infective, unlike Eimeria spp (coccidia) that sporulate in the environment.
Courtesy of Dr. Jean Sander.
Clinical Signs of Cryptosporidiosis in Poultry
The most common clinical signs of cryptosporidiosis in poultry include diarrhea and dehydration. In addition to causing diarrhea, the parasites can infect the respiratory tract and lead to coughing, gasping, airsacculitis, and sometimes death.
Clinical signs can last several weeks.
Diagnosis of Cryptosporidiosis in Poultry
Diagnosis of cryptosporidiosis in poultry is by microscopic examination of tissue scrapings or histological examination of the bursa, cloaca, and trachea. Lungs become gray and wet. The small (5-mcm-diameter) oocysts can be diagnostic but are difficult to see. Concentration of intestinal scrapings using saturated sugar solution and examination by phase-contrast or interference-contrast microscopy may improve visualization. Trained researchers or diagnosticians should provide positive identification. PCR assays have also been used but should not be the sole testing modality.
Pearls & Pitfalls
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Treatment of Cryptosporidiosis in Poultry
For cryptosporidiosis in poultry, no satisfactory control measures exist except isolation and good sanitation. None of the known anticoccidial drugs are effective.
Zoonotic Risk of Cryptosporidiosis in Poultry
Most Cryptosporidium spp that cause cryptosporidiosis in birds have not been confirmed as zoonotic; however, C meleagridis can infect both poultry and humans and is therefore considered zoonotic (2).
For More Information
Gerhold R. Parasitic Diseases. In: Greenacre CB, Morishita TY, eds. Backyard Poultry Medicine and Surgery: A Guide for Veterinary Practitioners. 2nd ed. Wiley; 2021:206-217.
References
Feng Y, Ryan UM, Xiao L. Genetic diversity and population structure of Cryptosporidium. Trends Parasitol. 2018;34(11):997-1011. doi:10.1016/j.pt.2018.07.009
Kabir MHB, Han Y, Lee SH, et al. Prevalence and molecular characterization of Cryptosporidium species in poultry in Bangladesh. One Health. 2020;9:100122. doi:10.1016/j.onehlt.2020.100122
Gong Z, Kan ZZ, Huang JM, et al. Molecular prevalence and characterization of Cryptosporidium in domestic free-range poultry in Anhui Province, China. Parasitol Res. 2021;120(10):3519-3527. doi:10.1007/s00436-021-07191-y
