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Dragoo Institute for the Betterment of Skunks and Skunk Reputations |
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Approximately 45,000 to 60,000 people die each year from rabies (Meslin, 1999). Between 1990 and 2000 a total of 31 people died from rabies in the United States (Krebs et al., 2000). Of those 31 deaths only one was from an unknown source and an unidentified virus strain. Eight were from a dog strain (3 unknown source, 5 dog bites), and 22 deaths resulted from a bat strain (20 unknown source, 2 bat bites). However, like skunks, not all bats are rabid. For more information on bats visit Bat Conservation International. While the actual number of human deaths as a result of rabies exposure is low in the United States, the costs associated with the disease run around $300 million annually (Centers for Disease Control and Prevention). These costs include disease detection (i. e. maintenance of rabies laboratories), prevention (vaccination pets, and pre-exposure for researchers studying rabies vectors), and control (animal control programs), and medical costs, such as those incurred for rabies post exposure prophylaxis (PEP). Rabies has been recognized for well over 4000 years (Baer, 1994).In addition to bats, the disease is maintained and transmitted by many terrestrial mammals, especially carnivores.Domestic, privately owned, community owned, and feral dogs are the primary reservoir of the rabies virus worldwide (Meslin, 1999).In the United States, however, because of an aggressive program to vaccinate pets, wildlife species are the predominant reservoirs and vectors of rabies.Rabies has been reported in skunks for at least 175 years (Parker 1975) and before 1990, striped skunks were the primary species responsible for reported cases of rabid animals in the United States. In 1990, raccoons became the species associated with the most cases of rabies reported in wildlife, followed by skunks (Krebs et al., 1995, 2000; Chomel, 1999).During 1999, 41% of all rabid animals reported to the CDC were raccoons and 29% were skunks (Krebs et al., 2000). Additionally, skunks suffer from an unsupported reputation as being rabies "carriers" that transmit but do not succumb to the virus. Skunks, like other mammals, die from rabies once symptoms occur. Once the virus begins shedding in the saliva, skunks have been shown to go as long as 6 days (usually less) before showing any clinical symptoms of the disease. Clinical signs of rabies in skunks can last from 1-18 days before the animal dies (Charlton et al., 1991). A skunk can be infected and harbor a latent form of the virus for up to 18 months (usually not longer than 2-6 weeks), but they cannot transmit the virus by biting before the virus reaches the salivary glands. There is no evidence of a true carrier state (Charlton et al., 1991). Skunks cannot excrete the virus in saliva and remain clinically free of symptoms for long periods of time, nor do skunks recover from clinical signs and continue to excrete the virus. If an animal is merely incubating the virus and bites someone, it will not transmit the virus. Unfortunately, at present there is no way to detect the latent form in an animal. Animals can be exposed to and contract the virus at any time. The amount of virus and the body part exposed have some affect on the time of incubation. For an animal to contract rabies, it has to be exposed to another animal that is shedding the virus, usually through a bite (Charlton et al., 1991). Presently, there are at least three recognized skunk strains of the rabies virus in the United States. The northern skunk strain found in the north central midwestern plains and eastern states is similar to the fox and dog strains of Texas and Arizona. The southern skunk strain occurs in the south central states. This strain is more similar to the raccoon strain found on the East Coast. A third strain occurs in California and is similar to the gray fox strain in Texas (Krebs et al. 1995). Recently, new strains of skunk rabies also have been found in Mexico (Loza-Rubio et al., 1999; de Mattos et al., 1999).Skunks do succumb to rabies in the eastern states as well, but the strain in that area is associated with rabid raccoons. Skunks are not yet known to maintain that strain in their populations, but issues of spillover and potential establishment are worrisome, because current oral vaccines targeting raccoons do not effectively immunize skunks (Tolson et al., 1987). Massachusetts and Rhode Island, where only the raccoon strain occurs, had more rabid skunks than raccoons reported in 1999 (Krebs et al., 2000), which suggests that the raccoon strain potentially could become enzootic in skunk populations. Additionally, in 2001 several skunks were diagnosed with a bat strain (big brown bat Eptesicus fuscus) of the rabies virus in Flagstaff, Arizona (2001 annual meeting of the Rabies in the Americas meeting, Ontario, Canada). Skunks are susceptible to the various strains of rabies found in terrestrial mammals and bats. Transfer of rabies virus from skunks to humans is a well-recognized health threat in urban areas.Striped skunks are often attracted to housing areas, due to the presence of pet food, water, garbage, and high populations of invertebrates in urban landscaping, and consequently are more likely to encounter humans and their pets. Striped skunks are believed to account for a substantial number of animal-to-human exposures (not infections) each year (Krebs at al., 1995). Most information on prevalence and molecular biology of the rabies virus in terrestrial wildlife comes from animals submitted for testing following human exposure. Little is known about the prevalence of rabies in natural populations, and how enzootic or epizootic levels of the disease interact with the ecology of various species (Greenwood et al., 1997; Krebs et al., 1995; Tinline, 1988). Moreover, data are needed on the population dynamics and genetics, space use, and mortality patterns of skunks in urban and remote areas to enhance our knowledge of the ecology and disease status of these species. For example, Greenwood et al., (1997) noted that 36 of the 40 cases of reported skunk rabies in North Dakota during 1992 would have gone unnoticed if not for their study. Much of the data regarding the ecology of skunks and rabies has been collected in Canada and the northern United States (Rosatte, 1984; Rosatte and Gunson, 1984a, 1984b; Rosatte et al., 1991; Rosatte et al., 1992; and Greenwood et al, 1997).Rosatte (1984) has demonstrated that rabies occurrences may be seasonal.In the winter female skunks will den together in communal dens thereby making rabies transmission easier. In addition to the increased contact, the stress involved with communal denning may contribute to the onset of rabies (Gunson et al., 1978; Rosatte, 1984; Verts, 1967). During breeding seasons skunks will interact with each other more frequently and the fierce breeding behavior is ideal for rabies transmission. Rabies in skunks occurs more frequently during the breeding season and females may be predominately more likely to become rabid (Rosatte, 1984). During the summer males are more solitary and females can be found with their young, but do not interact much with other conspecifics. The occurrence of rabies at this time of year is less detectable. Fall is the time of year that young skunks disperse.< They tend to be solitary, but do encounter other dispersing skunks. Additionally, other ecological factors may influence the spread of rabies and include such variables as population density, age structure, reproductive rate, survival rate, home range size, dispersal distances, and population genetics. What is important to remember about skunks and rabies is that not all skunks have rabies. A skunk that is aggressive and “attacks” someone should be tested (not just for rabies but for other diseases such as distemper as well). A skunk that is digging for grubs in the back yard and runs away when approached is acting like a normal skunk. We (as a society) are learning more and more about rabies. It is a disease that should be respected but not feared. There is a preventative that is virtually 100% effective if applied prior to the onset of rabies symptoms. Most people know when they have encountered a skunk, so death from skunk rabies is preventable. It is more likely that an unvaccinated pet will contract the skunk strain of rabies and pass that on to a human than it is to contract the skunk strain directly from a skunk. Vaccinate Your Pets! |
