The persistence of disease-carrying parasites in their state is concerning some Floridians. The parasitology unit of the National Veterinary Services Laboratories, the USDA, and researchers at the University of Florida recently initiated a roundup of ticks, prompted by new fears that cowdriosis (also known as heartwater disease) could spread from its foreign environment to the United States.
Cowdriosis is an acute, tick-borne, septicemic, rickettsial disease caused by Cowdria ruminantium. It can cause severe disease in cattle, sheep, goats, deer, and water buffalo. Largely native to sub-Saharan Africa and Madagascar, it also occurs in animals on some islands in the Indian Ocean and the Caribbean, and occasionally in Europe. Exotic breeds are highly susceptible to cowdriosis, making it one of the more threatening animal diseases in Africa.
Cowdriosis was in the news in May 1999 when Amblyomma sparsum (commonly known as large reptile ticks) were discovered in Florida on imported tortoises. The vector ticks can carry the rickettsial agent that causes disease.
The ticks removed from the tortoises were sent to be identified at a University of Florida laboratory in Zimbabwe, Africa, and some were discovered to carry C ruminantium. Fortunately, there have been no reports of the ticks transmitting the disease to any livestock or other ruminants in Florida.
An outbreak of cowdriosis in the United States would be disastrous to the beef and cattle industries. Mortality in susceptible species could be from 40 percent to approaching 100 percent. The disease can kill ruminants within two to three weeks of infection. There is no practical vaccine and no officially recognized treatment once the clinical disease is evident.
One factor that has increased the threat of cowdriosis is the growing popularity of imported reptiles as pets in the United States. More than 2.5 million reptiles were imported in 1995, according to the US Fish and Wildlife Service. More reptiles mean more ticks; some experts say there's almost no way to avoid ticks with imported reptiles. Advocates for federal regulations are pushing for stringent rules for imported reptiles.
Florida issued an emergency state rule in December banning the importation of any African spurred tortoises or leopard tortoises. Outstanding orders for shipment of this species have been canceled.
Prevention of the disease relies on control of its tick vectors. The USDA and NVSL are collecting ticks for further identification, research, and control. Any ticks - particularly those suspected to be exotic, collected from exotic animals, or collected from recently imported animals - should be sent to the USDA National Veterinary Services Laboratories, PO Box 844, Ames, IA 50010. The parasitology unit of the NVSL is the headquarters for the National Tick Surveillance Program and the USDA reference center for identifying animal ectoparasites.
Also ongoing is the Heartwater Research Project at the College of Veterinary Medicine at the University of Florida, funded through a grant from the US Agency for International Development, with laboratories in Zimbabwe. The project, designed to develop improved methods for the control and diagnosis of cowdriosis, was initiated in 1985 and is now in the fourth phase of development. Researchers involved with the project have completed development of a seriodiagnostic test. Primary objectives in this project include completing development of an inactivated vaccine and developing recombinant vaccines for the disease.
If researchers can eradicate the exotic rickettsia-transmitting ticks from our shores, part of the battle will be won. But another threat looms from within the United States.
Dr. Michael Burridge, professor with the University of Florida's Institute of Food and Agricultural Sciences and director of the Heartwater Research Project, warned that another parasite, the Gulf Coast tick, indigenous to the southeastern United States, has shown its capability to transmit the rickettsial agent that causes disease under experimental conditions. It's a tick that feeds on cattle and deer.
"If heartwater disease got in, we have our own ticks that could efficiently transmit it," Dr. Burridge said. "The stakes are very high. Our cattle industry would be in great trouble and it's a disease that's also deadly to deer."
When the JAVMA spoke to Dr. Burridge in January, he was preparing to travel to a congressional agricultural hearing in Florida on invasive species, to be chaired by subcommittee chairman Richard Pombo (R- Cal.). One of the primary topics will be on the exotic tick/disease situation, and Dr. Burridge will be there to answer questions raised by the subcommittee.
Dr. Burridge is a proponent of tougher regulations for imported reptiles. Unfortunately, tougher laws will not necessarily prevent illegal importation. He underscored the absurdity of the situation by pointing out that not only were the troublesome exotic tortoises being successfully bred in the United States, obviating the need to import them, but there's also rumored to be such an abundance of them here that they're being put out into the wild.
Another problem, he said, is that Florida has an optimal climate for ticks to multiply. "We've already found one established breeding population of the African tortoise tick in Florida," he said, adding that eradicating the ticks already here, is, in itself, an "enormous undertaking."
As Dr. Burridge sees it, there's no easy fix for the situation. "A task force of knowledgeable people need to deal with this as a matter of urgency."
To date, cowdriosis has not been diagnosed in the United States. Should we be nervous about ticks?
"It's a very serious problem," Dr. Burridge said. "We have every reason to believe from our research that recovered deer, like cattle, would become carriers. If the agent causing the disease got in, we'd have to live with it; therefore, it is essential that we take every effort to prevent its introduction."