$1.2 million NIH grant devoted to study leishmaniasis

Ames, Iowa-How can an infectious organism prevent the development of an effective cell-mediated immune response?

Leishmania amazonensis is a little protozoan that researchers postulatecan trick the immune system. Researchers at Iowa State University want toknow how the protozoan does it. The National Institutes of Health is justas interested. It will cough up $1.2 million over five years so Dr. DougJones can figure it out.

Jones, assistant professor of veterinary pathology at Iowa State University(ISU) tells DVM Newsmagazine, "It was discovered several years agothat there were different types of CD4 positive T cells. They call themTH-1, which promoted cell-mediated immunity, and TH-2 cells that promotedhumoral immunity like antibodies. Leishmania was a wonderful experimentalmodel to show the importance of these TH-1 cells in promoting a cell-mediatedimmune response in vivo," he says.

So why Leishmania amazonensis? Because it is inhibiting the immune response.

"Leismania amazonencis seems to inhibit the development of thisTH-1 response. It does that without having the CD-4 positive T cells, TH-2cells," he explains. "Somehow the parasite is inhibiting the developmentof this immune response, and we are trying to understand why that is andhow it happens," Jones adds.

Cuteneous leishmaniasis is prevalent and emerging in tropical and subtropicalregions of the world. Jones says the disease is burdensome to parts of theworld, but is different than the visceral form that has been linked to lastyear's Foxhound outbreak. Nonetheless, the disease is transmitted by thesandfly. The cutaneous form can present as a skin ulcer to facial disfigurations,organ failure and immune malfunctions.

Cutaneous leishmaniasis is an infection of the skin that produces multipleulcers or sores. The sores can lead to permanent scarring. This form ofthe disease is most common in South America and the Middle East. Very rarely,cutaneous leishmaniasis is reported in southern Texas.

The threat to dogs and people in the United States isn't that severe,but the benefit to successfully figuring out how this protozoan works onthe immune system could be applicable to other pathogens.

Jones explains, "The principles of immune evasion that the parasitesemploy are probably not unique to leishmania. They will be applicable toother pathogens that are agents of chronic infectious diseases, such asmycobacteria."

In fact, Jones likens this form of cutaneous leishmaniasis amazonensiswith Johne's disease in cattle.

Jones says there won't be any quick answers. "It's a beginning toa continued understanding. Once we start to understand the host side, wehave to understand how the parasite is making the host respond in this particularway."

While Jones adds that this particular disease may not wreak havoc incanine populations, it is a very real concern for many parts of the world.But in today's mobile society, it's important for veterinarians to keepup with emerging and global disease threats.