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Update on Parasitic Diseases Foreign to the U.S. Pete Teel and G. Gale Wagner, Texas A&M University Today, we are most concerned with Cattle Fever Ticks and Babesiosis, and African Bont Ticks and Heartwater. Boophilus ticks, or Cattle Fever Ticks, were eradicated following the combined state-federal tick eradication campaign in the first half of the 20th century (O.H. Graham and J.L Hourrigan, Journal of Medical Entomology, Vol.13, No. 6, pp. 629-658, 20 June 1977). Since that time, the U.S. has experienced an increasing number of outbreaks in Texas, away from the quarantine zone along the Texas-Mexico border. The risk factors associated with these outbreaks include: acaricide resistance, the expanding diversity of host animals, climatic changes, and trade. The risks associated with the re-emergence of fever ticks includes the risks associated with babesiosis. We assume that U.S. cattle will be highly susceptible; we know the disease is widespread in Mexico; we expect high mortality (>70%); there are no approved drugs for treating diseased animals, and there is no vaccine available to prevent the disease. Should babesiosis occur, the impact economic impact would include the costs of direct quarantine and eradication, estimated at $1.5 billion in the first year just in Texas (building dips, assembling cattle, indemnities, personnel, etc); potential death losses in cattle (we assume cattle are susceptible to the infection); and the assumption that a state like Texas would be quarantined (adjacent states close their borders - a national problem). African bont ticks (Amblyomma varieagatum) are also a worry. These ticks transmit the microorganism Cowdria ruminantium, the causative agent of heartwater in cattle. The U.S. has never had a known infestation of these ticks, although they are endemic to many of the Caribbean islands. Recently (August, 2000), bont ticks were discovered on cattle on St. Croix, a U.S. territory in the Caribbean. Cattle egrets are assumed to be involved in the spread of ticks between islands, since an experiment involving the dispersal of marked cattle egrets from Antigua, May 1989-December 1991, showed that egrets could travel as far as the Florida Keys (J.L. Corn, N.Barré, B. Thiebot, T.E. Creekmore, G.I. Garris, and V.F. Nettles, Journal of Medical Entomology, Vol.30, No. 6, pp. 1029-1037, 1993). As noted above, the risks associated with the introduction of Amblyomma ticks into the U.S. includes the risks associated with heartwater. Heartwater (Cowdria ruminantium infection of cattle) is historically a disease of ruminants in Africa, that has been recently diagnosed in ruminants in the Caribbean. We assume that U.S. ruminants are highly susceptible, and that we could expect a high mortality (>70%) should the disease be introduced. Heartwater is difficult to diagnose, and there are no approved drugs or vaccines available. While the heartwater agent is primarily transmitted by the African bont ticks (Amblyomma variegatum), we know that the Gulf Coast tick (Amblyomma maculatum), a native species, is a competent vector. We think that the likelihood of disease introduction is directly related to trade. The likelihood that Cattle Fever Ticks and Babesiosis, and African Bont Ticks and Heartwater is not a question of if, but when. Such critical issues require new approaches. The federal grant programs do not support work on foreign animal diseases, and a solution to the problem will require a long-term, multi-institutional, multi-disciplinary effort. Inherent in the solution is a policy on how to deal with acaricide resistant ticks, how to develop new technologies for tick and disease detection and control, and how to assess assess epidemiological and economic risks. We need new risk assessment, risk management and risk education, as well as the ability to integrate effective tactics into program strategies. "Bioterrorism: An International Challenge to Animal Agriculture" G. Gale Wagner, Texas A&M University. Bioterrorism/Agroterrorism, as a challenge to agriculture, assumes that U.S. animal agriculture might be a suitable target for economic sabotage by terrorists. Free trade in food animals and products makes U.S. animal agriculture and public health vulnerable to emerging pathogens and exotic diseases, either accidently (the risk increases as trade expands), or deliberately (bioterrorism/agroterrorism). Our purpose is to engage veterinarians, producers, USDA, diagnostic labs, but especially veterinarians, in a discussion process that makes them aware of the vital role they play in protecting the public health. The global issues that affect U.S. veterinarians, and producers alike include population growth, economic stagnation, and environmental stress; but also the escalating value of food animals and products in world markets, and the increased international movement of these commodities. At the national level, the challenges include:
There are numerous examples of bioterrorism. In 1915-16, German agents introduced anthrax and glanders into U.S. and Argentine horses. Plant toxins were used by the Mau Mau freedom fighters in Kenya to debilitate and kill cattle. The Rhodesian security forces used anthrax in cattle during the uprisings in 1978. More recently, Soviet military forces in 1983 infected horses in Afghanistan with glanders. New Zealand farmers managed to import viral hemorrhagic disease of rabbits in 1997 in an atempt to control the rabbit population. Viral hemorrhagic disease was also introduced (by an unknown source) into rabbits in Iowa in 1999. There are many agents that would make good candidates for bioterrorism:
On the other hand, there are the emerging diseases to consider. Recent examples include:
The impact of bioterrorism is overwhelming: In the U.S., we have a livestock and poultry industry worth $95 billion (1998), employing 24 million people in a farm to table industry. The U.S. is the world’s leading exporter ($54 billion in 1998), accounting for 15% of all global exports. If current disease epidemics serve as a guide, the current outbreak of FMD in the U.K. will be very expensive. BSE in the U.K. has cost $7 to 8 billion so far. A hypothetical FMD in a California dairy in 1998 cost $6 to 13 billion in the first month; $1 billion/day in lost trade. A hypothetical acaricide resistant tick outbreak in Texas in 1999 would have "cost" $1.5 billion in first year. Keep in mind that an "average" pound of meat travels 1000 miles on the hoof before it reaches the table, and the travel involves people, trucks, crates, bedding, clothing, etc. Would a disease agent be difficult to introduce? Consider that in the U.S. 30 cattle feeders have 50,000 to 500,000 cattle in feedlots; 6 pork producers have 100,000 to 700,000 sows in production; and 4 or 5 poultry companies have 3 to 5 billion birds. Biosecurity on the farm must consider the ability to quarantine incoming and sick animals, testing of incoming animals (especially imports), control of human and vehicle movement, and the control of pests and vectors. What are the critical control points? Consider the following: Ports of entry -
in 1999, USDA, PPQ considered: I am indebted to Terry Wilson et al (Emerging Diseases of Animals, Corrie Brown and Carole Bolin, eds., ASM Press, 2000) for much of the factual data used in this presentation. |