Cryptosporidiosis is a parasitic infection of the intestine associated with severe to chronic diarrhoea and caused by protozoa belonging to genus Cryptosporidium.
Distribution
Cryptosporidiosis is regarded as an important emerging disease worldwide. The parasite can be found anywhere in the environment contaminated by infected animal droppings or human waste, Cryptosporidium oocysts contaminate soil and water bodies as well as get into objects or surfaces that animals and humans do come in contact with and therefore, risk of infection is highest on exposure to potentially contaminated food or water.
Aetiology
The genus Cryptosporidium comprise obligate intracellular protozoan parasites belonging to the phylum Apicomplexa. The infective stage of the organism, the oocyst is about 3 micro meter in diameter. The organism has a wide host range and strains appear to be adapted to certain hosts can cause cross-strain infectivity with or without illness in the heterologous host species. Among the different species reported, C. parvum has been identified as the common cause of intestinal infection in several animals including calves, lambs, goat kids and piglets. Since similar strains of C. parvum have been associated with diarrhoea in humans, Cryptosporidiosis is of zoonotic significance.
Susceptible Hosts
Cryptosporidiosis has been reported from a wide range of host species such as humans, neonatal calves, lambs, goat kid, piglets, foals, rodents, birds, wild life species and companion animals. However, with the exception of C. parvum, incidence of diarrhoea with other species is rare. The severity of the disease is more in young animals and rare in adults.
Mode of Transmission
The disease is usually transmitted through the faeco-oral route and ingestion of the oocysts is the common source of infection. The infected animal sheds large quantities of oocysts for several days (around 3-12 days in calves) that contaminate the immediate environment. Oocysts are resistant to most disinfectants and can survive in cool and moist conditions for long periods. However, oocysts that dry out become non-infective in just a few hours. Transmission can occur from animal to animal through ingestion of contaminated food or water, or by contact with faecally contaminated environmental surfaces.
Pathogenesis
Factors like concurrent infection with enteropathogens and weakened immune systems (due to lack of colostrum feeding or stress resulting from extreme climate) predispose the young animal to severe disease. Following ingestion, the sporulated oocysts release the sporozoites (excystation) that invade the epithelial linings of the intestines. Subsequently, there are two cycles of asexual development resulting in the production of structures called meronants that contain either 8 (first generation) or 4 (second generation) merozoites. Thereafter, the merozoites then enter a sexual reproductive stage and the zygote is formed. The resulting zygote either develops into a thick-walled oocyst that will exit the host, or a thin walled oocyst that excysts in the host to start another life cycle. Unlike Eimeria sp. the thick walled oocyst sporulate within the host and are infective when passed along with faeces. The pathogenesis of diarrhoea is not known, but varying degrees of villous atrophy and damaged villous epithelium might be probable cause. While the small intestine is the most commonly affected site, symptomatic Cryptosporidium infections have also been found in other organs including other digestive tract organs, the lungs and possibly conjunctiva.
Clinical Findings
Intestinal Cryptosporidiosis is characterized by severe watery diarrhoea but may alternatively, be asymptomatic. Symptoms of Cryptosporidiosis generally begin 2 to 10 days (average 7 days) after becoming infected with the parasite. Clinical signs may range from mild to moderate diarrhoea that seems to persists in absence of proper therapeutic measures. The persistant diarrhoea is associated with a marked reduction of body weight, varying degrees of apathy, reduced feed intake and dehydration. However, case fatality rates are higher in immunodeficient calves exhibiting severe form of the disease.
Lesions
Lesions ususally observed are villous atrophy in large regions of ileum, caecum and colon. Large numbers of parasites appear embedded in microvilli of enterocytes and villi are shorter than usual. Infiltration of inflammatory cells is also evident in the intestinal linings.
Diagnosis
- Stool Microscopy: On modified acid fast staining, positive cases will show red round oocysts against blue-green background.
- ELISA (Enzyme linked immunosorbent assay).
- PCR (Polymerase chain reaction).
- Fluorescent antibody tests (FAT) on faecal smears.
- Histological findings: Identification of the parasite projecting from the brush border of the atrophied intestinal mucosal surface.
Treatment
There is no specific treatment for Cryptosporidiosis. Halofuginone (60-125 mg/kg body weight daily for 7 days) has been found to be effective in treatment of naturally infected calves. Symptomatic treatment in form of fluid therapy, antibacterial to rule out concurrent infections and feeding of small amounts of milk to optimize digestion and maintain body weight has been suggested. In dogs and cats, Paromomycin: 150 mg/kg SID for 5 days (dogs and cats), Tylosin: 10 to 15 mg/kg TID for 14 to 21 days (cats), Azithromycin: 5 to 10 mg/kg BID for 5 to 7 days (dogs); 7 to 15 mg/kg for 5 to 7 days (cats) and Nitazoxanide (200 mg BID for 5 days in animals 4 to 11 years old) have been used with some success.
Control
Provision of a clean area for cattle to calve.
Calves should be fed colostrum in adequate amounts from an early age.
Provision of dry and clean pen for calves.
Provision of clean drinking water and hygeinic food.
Destruction of mature oocysts using 5% ammonia, hyderogen peroxide, chlorine dioxide based reagents, 10% formol saline, etc.
Separation of healthy animls from sick ones and proper precautions to avoid mechanical transmission of disease.
Measures to enhance immune status of calves (by ruling out secondary bacterial infections, providing healthy diet and not exposing them to stress)
