Cryptosporidium hominis is a highly contagious parasite that lives in the intestines of infected humans. Since there are no effective treatments, it is a relentless public health concern.
"Sequencing the genome of Cryptosporidium will help us determine the underlying mechanisms of the organism's unusual resistance to antimicrobial agents, and enable us to develop preventive vaccines and/or pharmaceutical treatments," said Saul Tzipori, PhD, director of Tufts' Division of Infectious Diseases and a member of the multi-institutional team researching the genome.
Present in drinking and recreational water throughout the world, Cryptosporidium causes watery diarrhea that can lead to dehydration, weight loss, stomach cramps, fever, nausea, and vomiting. While healthy people usually overcome illnesses caused by the organism, it can be life threatening to malnourished children and people whose immune systems have been compromised because of cancer, AIDS, etc.
The Cryptosporidium pathogen, which can be found in the feces of both humans and animals, is difficult to work with, thereby impeding the efforts of investigators to conduct laboratory investigations and develop appropriate therapies.
Tufts researchers successfully isolated and propagated Cryptosporidium hominis in 2000, making Tufts the first research institution capable of propagating this pathogen.
In 2000, Tufts applied to the National Institutes of Health (NIH) for funding to enable a consortium of researchers at Tufts, Virginia Commonwealth University and the University of Minnesota to simultaneously sequence the genomes of two Cryptosporidium pathogens infectious to humans - Cryptosporidium hominis and Cryptosporidium parvum.
Today's article in the journal Nature describes the consortium's successful decoding of Cryptosporidium hominis - one of the two pathogens found in humans. In addition to producing DNA from the Cryptosporidium hominis isolate TU502, Tufts scientists constructed a bacterial artificial chromosome library for this research project. "This library is important for building a scaffold of the genome, on which the smaller sequence assemblies are aligned," said Giovanni Widmer, PhD, associate professor in Tufts' Department of Biomedical Sciences and a lead author of this study.
In April 2004, the consortium announced in the journal Science that it had successfully sequenced the eight chromosomes found in the genome Cryptosporidium parvum, the pathogen found in ruminants and humans.
"What is unique about this project is that the genomes of two related human and veterinary pathogens were sequenced in parallel," Widmer said. "This now puts us in a position to not only identify potential drug and vaccine targets, but also unravel key biological characteristics that might help explain the difference between the pathogen that infects humans only and C. parvum, which is transmitted between humans and animals."
Widmer recently received approximately $2 million from the NIH to continue studying Cryptosporidium hominis in collaboration with the Virginia team, which will increase the possibility of developing ways to prevent and/or treat illnesses caused by the pathogen. Through this funding, Widmer will examine the gene function in the infected host cells and determine their role and significance.
Since millions of Cryptosporidium germs can be released in a bowel movement from an infected person or animal, they can be found in soil, food, water, or surfaces that are contaminated with infected human or animal feces. Eating uncooked food or swallowing drinking or recreational water contaminated with the germs are typical ways people contract related illnesses.
The Cryptosporidium parasite is highly resistant to disinfectants such as chlorine and iodine. It is transmitted through oocysts, one of the stages of the organism's life cycle. Oocysts have tough protective walls, allowing them to survive under many environmental conditions. The U.S. Center for Diseases Control has classified Cryptosporidium parvum as a potential bioterrorism agent because it can withstand chemical water treatments and cannot be treated.
The U.S. Environmental Protection Agency reports that between 1986 and1994 Cryptosporidium was responsible for waterborne disease outbreaks in Nevada, Wisconsin, Oregon, Pennsylvania and Georgia that resulted in 416,651 illnesses and 123 deaths. The most severe outbreak during this time was in 1993 in Milwaukee, where more than 100 people died and more than 400,000 people became ill.
Tufts University School of Veterinary Medicine Background
Founded in 1978 in North Grafton, Mass., Tufts University School of Veterinary Medicine is New England's only veterinary school. It is esteemed for its pioneering academic programs, top notch clinical care services, and groundbreaking research that benefits animal, human, and environmental health. The school is a pioneer in veterinary ethics and values and offers the world's only graduate degree (M.S.) in the field of human/animal relationships and related public policies. Tufts University was the first institution of higher education to offer a four-year, combined doctor of veterinary medicine (D.V.M.) and master of public health (M.P.H.) degree. In 2004, Tufts Veterinary School began offering two new programs leading to master of science (M.S.) and doctor of philosophy (Ph.D.) degrees in comparative biomedical science. For more information, see: http://vet.