Rabies in wildlife

~Dr Suraksha S Deka, Dr D. Phangchopi, Dr Shiney George and Dr Anjan Jyoti Nath

 

Rabies is a viral zoonotic neuroinvasive disease which causes inflammation in the brain and is usually almost 100%fatal. Rabies is caused by various negative-sense RNA viruses of the Lyssavirus genus, which belongs to the Rhabdoviridae family. The genus is composed of 14 recognized species. The rabies virus, primarily infects mammals. In the laboratory it has been found that birds can be infected, as well as cell cultures from birds, reptiles and insects. Animals with rabies suffer deterioration of the brain and tend to behave bizarrely and often aggressively, increasing the chances that they will bite another animal or a person and transmit the disease. Rabies is usually transmitted to humans following a bite from an infected animal including bats, foxes, raccoons, jackals, and mongooses. Dogs are the most common source globally, while bats are the major source in the US and the Americas. Nonbite exposures are also possible and include being scratched, being licked over an open wound or mucous membrane, or being exposed to infected brain tissue or CSF.

In the following article we discuss the occurrence of rabies in the wild. Infected wildlife animals, often lose their fear of humans and become active during daylight hours, dramatically increasing the potential for human and domestic animal exposures.

Bats: Most of the recent human rabies cases in the United States have been caused by rabies virus from bats. In 1931, Dr. Joseph Lennox Pawan of Trinidad in the West Indies, a Government Bacteriologist, found Negri bodies in the brain of a bat with unusual habits.  In 1932, Dr. Pawan discovered that infected vampire bats could transmit rabies to humans and other animals. Globally bats are considered reservoirs of rabies virus, bats are generally non aggressive and avoids contact with humans. But safety measures are always advised for travelers and those who have have high chances of exposure or those who handle them. Not all bats have rabies but due to severity of the virus its always advised to take precaution.

Racoons: There have been several studies regarding rabies virus infection, with many specific to raccoon variant rabies. Raccoons represented 32% of the positive animals nationwide in 2012, 2013 and 2014, although there was a reduction in total numbers of positive raccoons detected for these years of 1.4%, 2.8% and 4.0%, respectivelyRaccoons can be infected with rabies and can turn aggressive toward people or animals. Raccoons  are known as one of the most common carriers of rabies – zoonotic disease – in the U.S. Most rabid raccoons start acting extremely aggressive and become dangerous to humans and pets. This pesky animal is classified as a rabies vector species. It means raccoon can not only carry but also transmit rabies.

Wolves: Though wolves are not reservoirs for the disease, they can catch it from other species. Wolves develop an exceptionally severe aggressive state when infected and can bite numerous people in a single attack. Under normal circumstances, wild wolves are generally timid around humans, though there are several reported circumstances in which wolves have been recorded to act aggressively toward humans. Wolf attacks, however, are rare , but there are many anecdotal reports from previous times. Attacks by wolves are generally directed against animals, such as cows and sheep, and for feeding purposes. Wolf attacks on humans are a little known and unexpected phenomenon.

Foxes :  Foxes are important vectors of rabies. As a consequence, a lot of research has been devoted to this topic. In 2002-05, 1,548 animal cases of rabies were registered in Europe. The incubation period of rabies in foxes is highly variable, from 11 days to 15 months, although usually it does not exceed 30 days. The morbidity phase is very short (0-14 days). The virus multiplies in the brain and salivary glands and is transmitted through biting. It has been found that up to 28 days before the onset of any symptoms, the disease can be transmitted from healthy-looking foxes incubating rabies. Anorexia and changes in behavior are typical clinical signs. The most visible sign is the loss of any fear of people, leading to reports of foxes in an infected area being more visible to humans. However, it is important to clarify that aggressive behavior towards humans is rare. The morbidity rate of foxes to rabies is considered to be 100%; there has been no report of any fox surviving infection.

Coyotes:  Coyotes are known carriers of rabies, which is spread through bites and scratches. The illness progresses quickly and early symptoms are similar to those of the flu. Infected individuals may also experience hallucinations, anxiety, tremors, uncontrollable salivation, and even paralysis as the virus attacks the central nervous system.An unprovoked attack by a coyote on a human is an extremely rare event, but this situation underscores the need to treat all animals with caution.

Other animals often found to have rabies include, skunks, weasels, badgers and mountain lions. In India, recently, two researchers from the Kerala Forest Research Institute codified and published reports on 21 cases of rabid mongoose attacking people in Edakkad, Kannur District, Kerala. As the attention on rabies control focuses on street dogs, there is also need to watch out for possible threat of wild populations getting infected and attacking human beings or livestock.

Management of rabies in wildlife is complicated by the ecologic and biologic factors associated with wildlife reservoirs, the multiagency approach needed to manage an important public health problem originating in wildlife, the limitations of available control methods, and the broad range of public attitudes toward wildlife. Previously population reduction was used to control rabies on the premise that densities of susceptible animals can be reduced below a threshold necessary for rabies to spread through populations. But this strategy is impractical considering ethical issues. Oral rabies vaccine for wildlife is available and is used in the United States. Oral rabies vaccine has become the essential tool for preventing geographical spread, control and elimination of rabies when the primary host is wildlife Surveillance is integral to all efforts of rabies control. Surveillance should be pursued more aggressively and with an analytic design during control field trials to objectively evaluate effectiveness. The general public should be better informed about avoiding direct contact with wildlife in general and with abnormally behaving and sick animals in particular. Any person bitten by a wild or domestic animal, particularly in areas where wildlife rabies is endemic, should seek medical attention.

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Authors: Dr Suraksha S Deka (Department of Veterinary Biochemistry), Dr D. Phangchopi (Department of AGB), Dr Shiney George, Dr Anjan Jyoti Nath   (Department of Veterinary Microbiology), Lakhimpur College of Veterinary Science, Assam Agricultural University, North Lakhimpur- 787051. Corresponding Author Email: surakshasubedi@gmail.com


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