Get your own Free Home PageNATIONAL ASSOCIATION of State Public Health Veterinarians, Inc.December 1, 1997
MEMORANDUM TO: State Public Health Veterinarians State Epidemiologists State Veterinarians FROM: Suzanne R. Jenkins, VMD, MPH, Chair Compendium of Animal Rabies Control, 1998 SUBJECT: Compendium of Animal Rabies Control, 1998 The National Association of State Public Health Veterinarians is pleased to provide the 1998 version of the Compendium of Animal Rabies Control for your use and for distribution to practicing veterinarians and officials in animal control, public health and agriculture in your state. This cover memo points out changes in the Compendium document and summarizes some of the discussions that took place during the Compendium committee meeting. COMPENDIUM CHANGES With the recent licensure of Raboral by the United States Department of Agriculture, a new category was added to the table of vaccines marketed in the United States. In addition to A. Monovalent (inactivated) and B. Combination (inactivated rabies), C. Oral (rabies glycoprotein. live vaccinia vector) was added. This necessitated changing Part I of the Compendium to reflect recommendations for parenteral vaccines only and moving the recommendation on the use of oral vaccine to Part III C. Control Methods in Wildlife. Raboral is a recombinant vaccine that has a portion of rabies virus genetic material inserted into a vaccinia virus. It is presently licensed for use in raccoons only. Because the vaccinia virus is live, the use of Raboral is restricted to "use in state or federal rabies wildlife control programs." Many state governments have developed or are in the process of developing guidelines for the use of this vaccine in their jurisdictions. The Compendium committee recommends that protocols for the use of Raboral include methods of evaluation and assessment so that data can be obtained to ascertain the most cost beneficial ways to use the vaccine as well as ways to address safety and public health issues. In Part III: Rabies Control, ferrets are now included with dogs and cats in all recommendations regarding vaccination, removal of strays, preexposure vaccination and management, interstate movement, licensure, postexposure management, and management of December 1, 1997 Page 2 animals that bite humans. These changes were unanimously agreed to by the committee after hearing a report on the final rabies viral study on ferrets in which a variety of bat rabies virus strains were used to infect ferrets (see addendum #1). Also in Part III, the statement "in areas where rabies is epidemic," was removed from B. 1. (b) Livestock and 2. Stray Animals because the committee agreed the recommendations in these two sections applied whether rabies was epidemic or not. Changes were also made to Part III B.5. (c) which refers to the postexposure management of other animals. A sentence which addressed animals currently vaccinated with a vaccine approved for use in that species was removed because the only species to which it applied was the ferret. A sentence was added to address special situations where valuable animals are routinely maintained in well managed confinement. BATS Bat rabies viral strains continue to represent the majority of rabies infections in humans (4 to date in 1997, see attached abstract). To understand the epidemiology of bat rabies and the role bats play in infecting humans and animals, laboratories are encouraged to identify the species of all bats that are tested for rabies and report this information to the Viral and Rickettsial Branch of the Centers for Disease Control and Prevention (CDC) either with the specimen or at a later date if that is more convenient. Bat conservations organizations, wildlife biologists in universities, or state wildlife agencies are usually very willing to assist in the speciation of bats. CDC reports that rarer species are under represented in their data base making interpretation of some data unreliable. There is also a lack of detailed information on the types of exposures that humans and animals are experiencing to rabid and non rabid bats. State and local health departments and rabies laboratories are urged to obtain and share as much of this information as possible. See addendum #2 for an updated Immunization Practices Advisory Committee (ACIP) statement regarding exposures to bats. WOLF HYBRIDS In an effort to resolve the issue of whether wolves and wolf hybrids are similar enough to dogs to be included on the labels of rabies vaccines for dogs without separate challenge studies for wolves and their hybrids, the United States Department of Agriculture (USDA) convened a meeting of taxonomists and other experts in April of 1996. Although participants agreed that rabies vaccines for dogs would probably protect wolves and their hybrids, there was some concern about the safetys of other vaccines, especially those with a modified live component. If USDA expands the species on rabies vaccine labels, it will have to do the same on all vaccines. December 1, 1997 Page 3 USDA has therefore requested that data on the safety of all especially modified live vaccines be provided to them for evaluation. They are looking for records from veterinarians and institutions that manage wolves. At the time of the Compendium meeting no data had been provided. SARCOMAS IN CATS The committee members and consultants heard a summary of the concerns, research, and public information on post vaccinal sarcomas in cats and concluded that there was a lack of sufficient definitive data to allow for specific recommendations. The committee felt strongly, however, that sarcomas are rare enough and rabies serious enough to state that the risk of a sarcoma developing in a cat does not outweigh the need to vaccinate all cats against rabies. SEROLOGY FOR SERUM NEUTRALIZING ANTIBODIES TO RABIES A number of foreign countries and the state of Hawaii are requiring a rabies virus neutralizing titer of 0.5 IU or greater for importation of domestic animals. Although the Rapid Fluorescent Focus Inhibition Test (RFFIT) is the one most widely used in this country, the test required for most importation is the Fluorescent Antibody Virus Neutralizing (FAVN) test. In comparative studies carried out by Kansas State University, both tests gave similar results, however the FAVN takes longer, is more labor intensive, and may be less safe for those performing the test due to the possibility of aerolization of the virus. In some cases the recipient jurisdiction may require two tests a month apart. When the initial test result is at or just above the required titer, the second test may have a result below the required antibody level requiring a longer quarantine period for the animal. Because measurements of antibodies after vaccination are an indicator of the animal's ability to respond to the vaccine, a drop in titer (especially a small one that may be due to laboratory variation) over time should not be interpreted as an inability of the animal to mount a response to rabies. Animals that have shown a response to a vaccination would be expected to have a good anamnestic response to the next vaccination. Practitioners may want to consider a booster vaccination near to the time the animal will be shipped to insure an adequate titer for both tests. The use of antibody titers for evaluating an animal for entry into a country may give the false impression that this is a measure of the animal's protection against rabies. Titers measure the animal's response to vaccine and cannot be considered an indicator of protection. If titers could be relied on to be a good measure of protection, challenge studies would not be necessary to license rabies vaccines for animals.It has been shown in a variety of situations that sometimes animals with high titers will not be protected and sometimes animals with low titers will be protected. At present, there is no way to differentiate a rising titer due to response to vaccine and one due to response to rabies infection. December 1, 1997 Page 4 HUMAN POSTEXPOSURE PROPHYLAXIS RabAvert, a purified chick embryo cell vaccine has been licensed for use in the United States and is being distributed by Chiron Corporation. At least 14 million doses of this vaccine have been used worldwide so it is not a new vaccine to the global market. The recommendation for the administration of human rabies immune globulin (HRIG) has been changed by the Immunization Practices Advisory Committee (ACIP) to the U.S. Public Health Service. The new language reads: "If anatomically feasible, the full dose of HRIG should be thoroughly infiltrated in the area around and into the wound(s). Any remaining volume should be administered intramuscularly at a site distant from the vaccine inoculation." HRIG supplies still appear to be limited. States that experience difficulty obtaining HRIG, which results in delayed treatment, are urged to write to the company and copy the National Center for Infectious Disease at CDC. The ACIP is planning to update the Recommendations for Rabies Prevention (last update was in 1991) to incorporate information on the new vaccine, the new HRIG recommendation, the new language for bat exposures, and other changes. PATHOGENESIS OF RABIES VIRUS VARIANTS IN DOMESTIC FERRETS SUMMARY OF PRELIMINARY DATA (as of 11/12/97) In the most recent studies using bat rabies variants to infect ferrets, results to date are as follows: rabies developed in 9 of 12 ferrets infected with a big brown bat rabies virus isolate; 10 of 12 infected with a Mexican free tailed bat isolate; 3 of 12 infected with a silver haired bat isolate; 1 of 6 infected with a red bat isolate; and 12 of 12 infected with a coyote isolate. The mean incubation period for the 23 rabid ferrets infected with bat strains was 22 days (range l0-44 days); the mean morbidity period was 3 days (range l to 6 days). Clinical signs included ataxia, lethargy, fever, paresis, paraparesis, paralysis and cachexia. Eleven of the 23 showed aggressive behavior. Five of the 23 contained rabies virus in their salivary glands and 1 of these shed virus in the saliva with onset of shedding concomitant with the recognition of clinical signs. For the 12 rabid ferrets infected with the coyote rabies virus variant the mean incubation period was 18 days (range 11 to 36 days) and the mean morbidity period was 4 to 5 days (range 2 to 6 days). Clinical signs included ataxia, lethargy, paresis, paralysis, myoclonus and fever. The majority of rabid ferrets 11 of 12 had signs of aggressive behavior. To date, 5 of 6 salivary glands contained virus and 3 ferrets shed virus in their saliva. This study is incomplete so these figures will change with time. Previous studies using skunk and raccoon rabies virus variants resulted in rabies mortality rates of 33 out of 50 ferrets (1 animal had clinical signs and recovered) that were given the skunk variant and 19 out of 51 given the raccoon strain. Mean incubation periods were 33 days (range 16-96 days) for the skunk variant and 28 days (range 17-63) for the raccoon variant. For ferret infected with the skunk variant, clinical signs included ataxia, lethargy, fever, paresis, paraparesis, paralysis and cachexia. Clinical signs in raccoon variant infected ferrets included inactivity, lethargy, constipation, hypothermia, ataxia, paresis, paraparesis, paralysis, and in 2 animals aggressive behavior. Rabies virus was isolated from the salivary glands of 1 of the 33 ferrets with rabies from the skunk strain and 12 of the 19 ferrets with rabies from the raccoon strain. None of the skunk variant infected animals shed virus in their saliva; 9 of the raccoon variant infected ferrets shed virus in saliva (largely concomitant with onset of clinical signs; 1 animal may have shed virus for as long as 4 days prior to recognizable signs). In summary, 88 of 155 ferret developed rabies. Twenty-three of the 88 had virus identified in the salivary glands and 13 of these shed virus in the saliva. In all but one case, shedding was concomitant with onset of recognizable signs; one animal may have shed virus for as long as 4 days prior to onset of signs. The longest an animal may have shed virus prior to death was 6 days. A confinement and observation period of 10 days after a ferret bites a person should be sufficient to protect public health. REVISED ACIP BAT RABIES POSTEXPOSURE PROPHYLAXIS (PEP) STATEMENT October 22, 1997 Bats are increasingly implicated as significant wildlife reservoirs for variants of rabies virus transmitted to humans. Recent epidemiological data suggest that transmission of rabies virus may occur from minor or seemingly insignificant bites from bats. The limited injury inflicted by a bat bite (in contrast to lesions caused by terrestrial carnivores) and an often inaccurate recall of the exposure history may limit the ability of health care providers to determine the risk of rabies resulting from an encounter with a bat. In all instances of potential human exposures involving bats, the bat in question should be safely collected, if possible, and submitted for rabies diagnosis. Rabies PEP is recommended for all persons with bite, scratch or mucous membrane exposure to a bat, unless the bat is available for testing and is negative for evidence of rabies. PEP may be appropriate even in the absence of demonstrable bite, scratch or mucous membrane exposure, in situations in which there is reasonable probability that such exposure may have occurred (e.g. a sleeping individual awakes to find a bat in the room, an adult witnesses a bat in the room with a previously unattended child, mentally challenged person, intoxicated individual, etc.). The likely effectiveness of PEP in this setting needs to be balanced against the low risk such exposures appear to present. This recommendation, used in conjunction with current ACIP guidelines, should maximize a provider's ability to respond to situations where accurate exposure histories may not always he obtainable, while still minimizing inappropriate PEP.
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