Mar. 6, 2000 CHAMPAIGN, Ill. -- Veterinary scientists have proved that an organism long suspected as the cause of feline infectious anemia (FIA) indeed is the culprit. Along the way, they have created a diagnostic tool and concluded that the bacterial organism is a mycoplasm, not a Rickkettsia.
The molecular confirmation that FIA is caused by Haemobartenella felis -- described in an article in the January issue of Veterinary Pathology -- came after a series of studies at the University of Illinois College of Veterinary Medicine. Using a technique known as in situ hybridization, researchers showed that a small gene fragment, which they had identified earlier, linked positively to H. felis located on red blood cells taken from experimentally infected cats.
"These organisms are teeny tiny parasites," said Joanne B. Messick, a UI professor of veterinary pathology. "For years they were thought to be rickettsial, but our laboratory and at least two other laboratories now show that they are not rickettsial. They are mycoplasma organisms."
Rickettsia is a gram-negative, disease-causing intracellular parasitic bacterium whose transmission has been linked to fleas, ticks, mice and lice. Mycoplasma organisms are tough, evasive bacteria that lack a cell wall. They are the smallest free-living cells known to exist, and their vector is uncertain, though believed to be the same as Rickettsia, Messick said.
For years, suspected cases of FIA have been treated with antibiotics. Cats can become very anemic as red-blood-cell counts plummet. Even if symptoms disappear, the organism remains present. The prevalence of the disease -- lacking a diagnostic tool -- has been impossible to determine.
Messick and colleagues, including UI veterinary student Linda Marie Berent, initially developed a PCR (polymerase chain reaction) assay, then used it to see if it could detect H. felis in infected cats. "Dr. Berent has used the PCR assay to answer some questions related to whether cats remain carriers after infection and to prove that the clinical disease is caused by H. felis," Messick said.
The UI technique will help veterinarians better grasp the scope of FIA infection, she said. It also will help researchers find the carrier and identify risk factors associated with chronic infection. Once the genes involved in disease activation are isolated, she said, a vaccine could be made. She will discuss her lab's findings and the implications during a seminar May 25-28 at the 18th Annual American College of Veterinary Internal Medicine Forum in Seattle.
"In the cat population, I believe the disease is a bigger problem that people recognize," she said. "It has been too difficult to diagnose. It's a really fascinating organism. It is very transient. It goes into hiding very easily. Where does it go?"
Long-term infections with mycoplasmas relate to rheumatic diseases such as arthritis, she said. "However, the long-term consequences of a cat living with H. felis, even if inactive, are unknown."
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