An Ecological Strategy for Controlling Bovine Rabies through Elimination of Vampire Bats

Because of the limited resources of most Latin American countries, an ecological strategy for controlling bovine rabies through elimination of vampire bats is proposed instead of attempting total eradication. The strategy is essentially a combination of one or more of the anticoagulant control techniques applied with knowledge of the epizootiology of vampire rabies. Since rabies outbreaks in vampire bats are migratory, each outbreak is studied to determine the direction and velocity of its course, then an area is selected in its path where vampires are eliminated, forming a barrier and resulting in elimination of the outbreak. Since the publication in 1972 of two new and quite effective techniques for eliminating vampire bats through different methods of administering anticoagulant (Linhart 1972; Thompson 1972), there has existed the reasonable feasibility for controlling bovine rabies in Latin America. Both the U.S. AID and the Pan American Health Organization have sent specialists throughout South and Central America teaching the techniques. Yet today bovine rabies remains an important adverse factor impeding development of the cattle industry from Mexico to Argentina. The reason is the impracticality of attempting widespread elimination of the species. In most countries where vampire control teams exist, efforts are scattered and sporadic, tending to respond to alarm situations. Likewise where teams attend to outbreaks of bovine rabies, their efforts are mistakenly directed to those ranches where cattle have died. This report outlines an ecological strategy for controlling bovine rabies which is economically feasible for most countries. The method has been successfully applied in Venezuela and Brazil. Understanding the ecological strategy suggested here requires a comprehension of the epidemiology of rabies in vampire bats as well as some knowledge of the social behavior of this species. Bovine rabies is caused by the same virus causing rabies in dogs and other animals. The principal vector of bovine rabies in Latin America is the common vampire bat (Desmodus rotundus). The disease has been known since the Spanish Conquest, when men and horses were bitten by vampires and contracted rabies. There is little relationship between bovine and canine rabies since the ecology of the virus differs greatly within different hosts. Clearly, when a rabid dog, fox or skunk bites a cow, it may later succumb to rabies; but the theme of this paper is the control of the disease produced by rabid vampire bats. The name of the disease varies from country to country, and bovine rabies has long been known as "rabia paralitica bovina" (bovine paralytic rabies), or frequently "rabia paresiante" (paralytic rabies), while in other countries it is known as "derriengue", "mal de caderas", "tumbi baba", etc. The symptoms of this disease in cattle may be confused with other diseases, such as Aujesky's disease, tick bite paralysis, encephalitis, and others. The only accepted diagnostic tests are those made with tissues; that is, fluorescent antibody technique, mouse innoculation, and Seller's test, all with cerebral material from suspect animals. Today the disease is found throughout the distribution of the vampire bat, that is from central Mexico in the north, throughout Central and South America to northern Argentina. From the ecological viewpoint, those regions where vampires are found have suffered many changes since the arrival of Europeans to the Americas. Many of these changes have favored the vampires. Today there are many large domestic animals where previously there were few or none. Likewise of importance is the increase of sites which can serve as roosts such as mines, tunnels, wells, barns, etc. Today there are probably many more vampires than previously and their concentrations favor the spread of disease. With the opening of new virgin lands for cattle future losses will increase. In the past, with the exception of one technique (Greenhall 1964), in order to apply control methods, such as the use of fire, dynamite, insecticides, etc. the principal problem lay in the difficulty of finding most of the vampire roosts. Thus control of bovine rabies through controlling the vector, the vampire bat, was not feasible. Consequently, effective programs were based on cattle vaccination. The vaccine is effective in respect to saving the life of the vaccinated cow, but since cattle play no role in the epizootiology of rabies in vampires, outbreaks continued as a potential danger to non-vaccinated animals and man himself. In recent years advances in the field of control of hematophagous bats and also in knowledge of the epizootiology of rabies in these vectors, offer together hope for the effective control of bovine rabies through strategic elimination of these vectors. Linhart et al. (1972) have demonstrated a new method of control of vampires utilizing topical treatment with an anticoagulant. The treated bats return to their roosts where they contaminate others of the colony, frequently eliminating all. In the first tests, chlorophacinone was used at 50 mg per 1.5 ml of vaseline; later others have used various anticoagulants with success: diphacinone at 15 mg/ml, and warfarin at 50 mg/ml. The latter two substances are most frequently used now. EPIDEMIOLOGY OF RABIES IN VAMPIRE BATS Until the publication by Lopez et al. (1969) there was no observable pattern in the epizootiology