Cryptosporidiosis is a substantial threat to HIV infected individuals, who have a lifetime risk of infection of around 10 per cent15
. Cryptosporidiosis remains an important cause of diarrhoea in the immunocompromised due to the lack of effective therapy. Although cryptosporidiosis in HIV infected patients has been widely reported in India including three reports from our centre4,5,10,16-21
, little is known about circulation and transmission patterns of the infection in this part of the world. Studies from developed countries have found sexual behaviour patterns, immigrant status, pet ownership especially dogs and farm animals, travel outside the country, toileting children and some ethnic populations to be some of the risk factors associated with cryptosporidiosis6-9,22
. In developing countries, one case-control study from Guinea-Bissau23
found that significant risk factors were keeping pigs and dogs and storage of cooked food for later consumption. Breastfeeding was negatively associated with risk. However, animal-human mixing patterns, access to potable drinking water and antiretroviral therapy are all factors that play a major role in the risk of acquiring cryptosporidiosis and are different from region to region. Molecular typing data from our centre10
indicated that though C. hominis
was the most common species identified, other zoonotic species were also relatively common in HIV infected individuals and so raised questions about the sources of infection. A previous report analyzing isolates from Kenya, Switzerland and the United States identified animal contact in patients (using a questionnaire) infected with zoonotic isolates24
, but this association was not clearly seen in our study. However, the information on animal contact was based on a response to the questionnaire from the patient so casual animal contact not reported by the study participant cannot be ruled out in all cases. While the most common species associated with human cryptosporidiosis is C. hominis
, several studies indicate that immunocompromised individuals are susceptible to a wider range of species and genotypes and that host factors may play a role in controlling susceptibility to these divergent parasites25,26
. Immunodeficiency therefore, alters host susceptibility to Cryptosporidium
spp. that are not normally infectious in humans1
. Additionally, variation in virulence among different species has also been demonstrated in volunteer studies with respect to attack rate and duration of diarrhoea27
. Considerable circumstantial evidence from previous studies have shown a zoonotic exposure in these patients28
, so the poor association with animal exposure in our study indicates that these potentially zoonotic species circulate in the human population but will require further studies involving characterization of isolates from infected animals. Although no statistically significant association was found between most of the risk factors studied and acquisition of cryptosporidiosis in these patients, further studies with a larger number of HIV infected adults for whom more extensive follow up data are available, will be required. This will help in understanding the transmission and natural history of cryptosporidiosis in India. It is necessary to document the public health significance of this infection in immunocompromised hosts in order to formulate more rational approaches to the control of this disease, especially in the developing countries.
It must be noted that these studies can be difficult to conduct because of the stigmatizing nature of the illness. During the course of this study, many problems were encountered because patients did not return for scheduled visits to hospital and when home visits were made, it was discovered that patients had moved or provided incorrect addresses. Such problems have also been encountered by other investigators, who have shown that approximately 70 per cent of individuals return for the results of HIV related tests and less than 50 per cent participate in further studies29,30
In conclusion, cryptosporidiosis is an important cause of diarrhoea and associated morbidity in HIV infected individuals. Further studies need to be done with a larger sample to understand risk factors associated with zoonotic transmission of Cryptosporidium spp. in the population.