diarrhea, parasitic infection, prevention, zoonoses
E Gorospe. Updates on the Environmental Risks and Control of Cryptosporidiosis. The Internet Journal of Infectious Diseases. 2005 Volume 5 Number 1.
Cryptosporidiosis is an emerging infectious disease that remains to be fully understood. The role of environmental issues such as water quality, livestock management, animal waste disposal and insect control are beginning to be recognized in the transmission of cryptosporidiosis. Prevention is highly emphasized as there is no consistently effective pharmacologic treatment for human cryptosporidiosis until now. Based on literature review, there are four environmental strategies in controlling cryptosporidiosis: (1) promotion of hygienic practices in the livestock industry (2) sanitary disposal of animal manure and human waste (3) constant surveillance of water supply and (4) protection of the immunocompromised population. More studies are needed to further understand the ecological factors that may contribute to the effective measures in controlling cryptosporidial transmission and infection.
Cryptosporidiosis is an emerging infectious disease which involves several environmental health issues such as water quality, control of zoonotic transmission and environmental health policy. It is a self-limiting diarrheal disease which can develop into a life threatening infection for the immunocompromised. Primarily recognized as a zoonotic infection, cryptosporidiosis has been reported all over the world to cause significant burden of disease. The greatest toll occurs among those with HIV/AIDS, post-transplant immunosuppression, malignancies, the frail elderly and the very young. These issues are essential in fully understanding the zoonotic potential of Cryptosporidium. It forms the basis for evidence-based recommendations that could be transformed into rational and effective environmental policies.
Review Of Literature
It was in 1907 when Ernest Tyzzer first described cryptosporidiosis in laboratory mice . In the early 1970s, cryptosporidiosis was considered as a veterinary disease affecting turkeys and cows . Only in 1976 was cryptosporidiosis identified to cause disease in humans [3, 4]. It is increasingly being recognized as a significant cause of diarrhea, intestinal malabsorption and mortality among malnourished children worldwide .
The taxonomy of this organism has been traditionally based on morphology but the advent of advanced molecular techniques has led to the identification of other species and reorganization of the taxonomy . As of 2004, there are 22 identified species. There is no strict host specificity as other species once thought to infect poultry, domestic animals and mice only have been found in humans as well .
The clinical course and severity of infection varies individually based on immune status. Immunocompetent individuals may have asymptomatic illness, abdominal discomfort, anorexia, nausea or watery diarrhea that normally persists for two to three days. In contrast, patients with immune deficiencies can have chronic, life threatening, and disseminated cryptosporidiosis. They may have profuse watery diarrhea that can persist for more than two weeks. An unusual complication is the development of gas-filled cysts in the intestinal walls which could rupture and cause life-threatening peritonitis . The infection could also disseminate into the biliary tract, the pancreas and even in the lungs and sinuses .
Among HIV patients complaining with diarrhea, the worldwide prevalence of cryptosporidiosis is estimated at 32% . Only 29% of immunocompromised patients with cryptosporidiosis experience remission. It is also being implicated as a cause of chronic diarrhea among cancer patients.
There is no consistently effective treatment for cryptosporidiosis. Some experimental drugs need to reach toxic human doses in order to reduce the parasite. Paromomycin, previously used in bovine cryptosporidial diarrhea , has inconsistent results on humans . Nitazoxanide, a new thiazolide antiparasitic has just been approved by the U.S. Food & Drug Administration for cryptosporidiosis in children. Its use for the immunocompromised is still being evaluated . For most HIV/AIDS patients, enhancement of immune response by increasing CD4+ T-lymphocyte count remains as the most effective strategy in controlling disseminated cryptosporidiosis . Since no effective treatment is available, the emphasis of public health programs regarding cryptosporidiosis relies heavily on preventive strategies such as assuring water safety and strengthening individuals' immune defenses.
More than half of human cryptosporidiosis is attributed to
Bodies of water that receive sewage from cattle grazing areas have increased concentrations of oocysts . As we concentrate more livestock in a geographic locality due to increasing food demand, we are also increasing the load of oocysts in the environment. In the U.S. alone, the estimated annual cattle manure production is 1.2 Billion tons .
Recent discoveries in the transmission of cryptosporidiosis also suggest involvement of flies. Synanthropic insects such as houseflies and other common filth flies have been documented in several studies to carry
Drastic weather changes have also been implicated in the propagation of oocysts. Increased concentration of oocysts have been observed to coincide with heavy rainfall  such as the outbreaks in Milwaukee, Wisconsin and in other foreign countries. Flood water can flow from contaminated lands towards surface water for domestic use. In the Milwaukee outbreak, contamination of Lake Michigan with human and animal waste that may have overwhelmed the local water treatment process . Similarly, Las Vegas is being supplied by Lake Mead and there have been sporadic reports identifying oocysts from the lake .
Recognizing that animal manure is a major contributor of
First, livestock industries should be constantly reminded of the threat of zoonoses from farm animals. Ramirez et al. suggest limiting the number of animals in enclosed facilities to limit animal transmission and oocysts load . Animal facilities should be zoned away from waterways that are sources for the local community's drinking water supply. The goal is to reduce run-offs from animal farms. Grass or strips of vegetation on the edges of surface water may serve as natural buffer zones. They could trap sediments and reduce the organic matter that could contaminate the water .
Second, cattle manure should be promptly and safely disposed. Flies can carry oocysts to human water and food sources. Physical barriers such as insect screens and other environmental control strategies should be placed in areas where animal manure is densely concentrated. The same strategies also apply in managing human wastes. After all, the safe disposal of human and animal wastes has been a standard tenet in public sanitation.
Third, constant surveillance of water supply is advised as more studies are needed to understand the waterborne properties of
Lastly, immunocompromised individuals should avoid contact with animals that are host or carriers of
Cryptosporidiosis is an emerging infectious disease. The organism has physical characteristics that enable it to survive in standard water processing. Various environmental agents play a role in its transmission including flies and livestock. More studies are needed to understand the nature of the organism in terms of its detection and viability in water treatment processes. Prevention is still the primary and most effective strategy. The role of the environment can not be disregarded as climatic changes, increased demand for livestock production and pollution of our water reservoirs increasingly threatens human health.
Emmanuel C. Gorospe, MD The Children's Nephrology Clinic 3201 S. Maryland Parkway, Suite 606 Las Vegas, NV 89109 Tel no: (702) 743-7332 Tel no: (702) 639-1717 Email: GorospeE@unlv.nevada.edu