Rabies is a viral zoonotic neuroinvasive disease which causes inflammation in the brain and is usually fatal. Rabies, caused by 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. Most cases of humans contracting the disease from infected animals are in developing nations. Every year, over 55, 000 human fatalities are attributed to rabies.
Stages of disease
Three stages of rabies are recognized in dogs and other animals.
- The first stage is a one- to three-day period characterized by behavioral changes and is known as the prodromal stage.
- The second stage is the excitative stage, which lasts three to four days. It is this stage that is often known as furious rabies due to the tendency of the affected animal to be hyperreactive to external stimuli and bite at anything near.
- The third stage is the paralytic stage and is caused by damage to motor neurons. Incoordination is seen due to rear limb paralysis and drooling and difficulty swallowing is caused by paralysis of facial and throat muscles. This disables the victim's ability to swallow, which causes saliva to pour from the mouth also the reason bites are the most clear way for the infection to spread is because the virus is most concentrated in the throat and cheeks causing major contamination to saliva. Death is usually caused by respiratory arrest.
Mammals
Bats
Bat-transmitted rabies occurs throughout North and South America but it was first closely studied in Trinidad in the West Indies. This island was experiencing a significant toll of livestock and humans alike to rabid bats. In the 10 years from 1925 and 1935, 89 people and thousands of livestock had died from itâ€"“the highest human mortality from rabies-infected bats thus far recorded anywhere.â€
In 1931, Dr. H. Metivier, a Veterinary surgeon, established the connection between the bites of bats and paralytic rabies and 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. In 1934, the Trinidad and Tobago Government began a program of eradicating vampire bats, while encouraging the screening off of livestock buildings and offering free vaccination programs for exposed livestock.
After the opening of the Trinidad Regional Virus Laboratory in 1953, Arthur Greenhall demonstrated that at least eight species of bats in Trinidad had been infected with rabies; including the Common Vampire Bat, the rare White-winged Vampire Bat, as well as two abundant species of Fruit Bats: the Seba's Short-tailed Bat, and the Jamaican Fruit Bat.
Non-bite transmission of rabies in people has been reported by the CDC, and experimentally demonstrated with a high efficiency in susceptible animals placed in bat-proof and insect-proof cages in a cave with bat colonies by Constantine in Frio Cave, Texas, as early as 1960. In 1967, rabies virus was isolated from the air in the same cave, presumably passed by the bats urinating, potentially forming a source for infection of other susceptible animals, and presenting a hazard to researchers and spelunkers. While the risks may be low, they are deserving of further study and monitoring.
The United Kingdom, which has stringent regulations on the importation of animals, had also been believed to be entirely free from rabies until 1996 when a single Daubenton's bat was found to be infected with a rabies-like virus usually found only in bats: European Bat Lyssavirus 2 (EBL2). There were no more known cases until September 2002 when another Daubenton's bat tested positive for EBL2 in Lancashire. A bat conservationist who was bitten by the infected bat received post-exposure treatment and did not develop rabies.
Then in November 2002 David McRae (1947â€"2002), a Scottish bat conservationist from Guthrie, Angus was bitten on the ring finger of his left hand by a bat, thereby becoming the first human to contract rabies in the United Kingdom since 1902. He subsequently died in a hospital from EBL2 rabies on November 24, 2002.
In November 2004, Jeanna Giese, a fifteen-year-old girl from Fond du Lac, Wisconsin, became one of only six humans known to have survived rabies after the onset of symptoms, and the first known instance of a human surviving rabies without vaccine treatment. Giese's disease was already too far progressed for the vaccine to help, and she was considered too weak to tolerate it. Doctors at the Children's Hospital of Wisconsin in Wauwatosa, a suburb of Milwaukee, achieved her survival with an experimental treatment that involved putting the girl into a drug-induced coma, and administering a cocktail of antiviral drugs. Giese had symptoms of full-blown rabies when she sought medical help, thirty-seven days after being bitten by a bat. Her family did not seek treatment at the time because the bat seemed healthy. Jeanna regained her weight, strength, and coordination while in the hospital. She was released from the Children's Hospital of Wisconsin on January 1, 2005.
On May 12, 2006, Harris County, Texas Health Department officials reported that a teenage boy, Zachary Jones of Humble, Texas, had died of rabies at Texas Children's Hospital in Houston, Texas. Zachary had contracted the disease after a bat flew in his bedroom and bit him in his sleep. He was unaware he had been bitten and was not hospitalized until he developed symptoms several weeks later. He died at Texas Children's Hospital after an attempt to cure the disease through a drug-induced coma, similar to that of Jeanna Giese.
In August 2006, a 73-year-old rural resident located east of Edmonton, Alberta, Canada was bitten by a bat while he slept. He ignored the bite and became symptomatic in January 2007. Diagnosed with rabies in March 2007, he was treated with the Milwaukee protocol, but died April 26, 2007.
On August 6, 2006, 950 Girl Scouts were urged to receive rabies shots by the Girl Scouts of the USA. The nine hundred and fifty girls had attended a camp in Virginia, U.S.A. in July, and had reported seeing bats in their cabins. Even though infections were relatively unlikely, the GSA offered to pay for the shots, at a cost of nearly two million dollars. The Centers for Disease Control reports 27 cases of human rabies caused by the bat variant rabies virus in the United States from 1990 to 2002.
On December 8, 2007, a 34-year-old Dutch medical doctor died from rabies. According to Dutch media, the woman, who worked at the Amsterdam Academic Medical Center (AMC), had been attacked by a small bat while on holiday in Kenya the previous October. The attack, which occurred at a camping site somewhere between Nairobi and Mombasa, resulted in some bleeding scratches on her nose. She was infected with Duvenhage virus and succumbed to severe brain infection.
In August 2010, a migrant worker died in a Louisiana hospital from a rabid vampire bat bite that occurred while the man was in Mexico.
Coyotes
Rabies is also common in coyotes and can be a cause for concern if they interact with humans.
Cats
Rabies is common in cats. In the United States between 200-300 cases are reported annually. Cats that have not been vaccinated and are allowed access to the outdoors have the most risk for contracting rabies as they may come in contact with rabid animals. Feral cat populations are commonly affected by the rabies virus. The virus is often passed on during fights between cats or other animals and is transmitted by bites, saliva or through mucous membranes and fresh wounds. The virus can incubate from one day up to over a year before any symptoms begin to show. Symptoms have a rapid onset and can include unusual aggression, restlessness, lethargy, anorexia, weakness, disorientation, paralysis and seizures. To prevent rabies in outdoor cats it is important to vaccinate and booster felines by trusted veterinarian with a licensed rabies vaccine.
Rabbits
Rabbits are particularly vulnerable to the rabies virus. The virus is often contracted when attacked by other rabid animals and can incubate within a rabbit for up to 2â€"3 weeks. Symptoms include weakness in limbs, head tremors, nasal discharge, low of appetite, nasal discharge and death within 3â€"4 days. However, there are currently no vaccines available for rabbits. It is recommended that rabbits be kept indoors or enclosed in hutches outside that do not allow other animals to come in contact with them. In the 1880s, rabbits were used to develop the first rabies vaccine by Louis Pasteur.
Dogs
Rabies has a long history of association with dogs. The first written record of rabies is in the Codex of Eshnunna (ca. 1930 BC), which dictates that the owner of a dog showing symptoms of rabies should take preventive measure against bites. If a person was bitten by a rabid dog and later died, the owner was fined heavily.
Three stages of rabies are recognized in dogs. The first stage is a one- to three-day period characterized by behavioral changes and is known as the prodromal stage. The second stage is the excitative stage, which lasts three to four days. It is this stage that is often known as furious rabies due to the tendency of the affected dog to be hyperreactive to external stimuli and bite at anything near. The third stage is the paralytic stage and is caused by damage to motor neurons. Incoordination is seen due to rear limb paralysis and drooling and difficulty swallowing is caused by paralysis of facial and throat muscles. Death is usually caused by respiratory arrest.
Horses
Rabies can be contracted in horses if they interact with rabid animals in their pasture, usually being bitten on the muzzle or lower limbs. Signs include aggression, incoordination, head-pressing, circling, lameness, muscle tremors, convulsions, colic and fever. Horses that experience the paralytic form of rabies have difficulty swallowing, and drooping of the lower jaw due to paralysis of the throat and jaw muscles. Incubation of the virus may range from 2â€"9 weeks. Death often occurs within 4â€"5 days of infection of the virus. There are no effective treatments for rabies in horses. Veterinarians recommend an initial vaccination as a foal at three months of age, repeated at one year and given an annual booster.
Opossums
Experimental studies of rabies infection in the Virginia opossum have shown the importance of the mode of transmission. Opossums became infected when exposed to air-borne virus but were found to be fairly resistant to intramuscular inoculations. The aerosol transmission of rabies in opossum was investigated following the death from rabies of two men who had visited the Frio Caves, Texas, and did not remember any direct contact with bats.
Rabies cases in the Virginia opossum are spillover cases from other wildlife species such as bats, skunks and the raccoon epizootic in the eastern United States. Cases have been reported across the United States from California to New York. In New York state, laboratory confirmed rabies cases in opossums occurred five of the ten years between from 1989 to 1999. Recently, from 2010 to 2014, rabid Virginia opossums were reported in New York City and the states of New Jersey, Maryland, and Virginia.
Skunks
In the U.S., there is currently no USDA-approved vaccine for the strain of rabies that afflicts skunks. When cases are reported of pet skunks biting a human, the animals are frequently killed in order to be tested for rabies. It has been reported that three different variants of rabies exist in striped skunks in the north and south central states.
Humans exposed to the rabies virus must begin post-exposure prophylaxis before the disease can progress to the central nervous system. For this reason, it is necessary to determine whether the animal, in fact, has rabies as quickly as possible. Without a definitive quarantine period in place for skunks, quarantining the animals is not advised as there is no way of knowing how long it may take the animal to show symptoms. Destruction of the skunk is recommended and the brain is then tested for presence of rabies virus.
Skunk owners have recently organized to campaign for USDA approval of both a vaccine and an officially recommended quarantine period for skunks in the United States.
Wolves
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. The majority of fatal wolf attacks have historically involved rabies, which was first recorded in wolves in the 13th century. The earliest recorded case of an actual rabid wolf attack comes from Germany in 1557. 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. Before a vaccine was developed, bites were almost always fatal. Today, wolf bites can be treated, but the severity of rabid wolf attacks can sometimes result in outright death, or a bite near the head will make the disease act too fast for the treatment to take effect. Rabid attacks tend to cluster in winter and spring. With the reduction of rabies in Europe and North America, few rabid wolf attacks have been recorded, though some still occur annually in the Middle East. Rabid attacks can be distinguished from predatory attacks by the fact that rabid wolves limit themselves to biting their victims rather than consuming them. Plus, the timespan of predatory attacks can sometimes last for months or years, as opposed to rabid attacks which end usually after a fortnight. Victims of rabid wolves are usually attacked around the head and neck in a sustained manner.
Foxes
Recently (probably from the late 90s, by mentions in press) new symptoms of rabies of wild animals have been observed, namely in foxes. Probably at the beginning of the prodromal stage foxes, who are extremely cautious by nature, absolutely lose wild instincts. Animals come into settlements, reach for people, and behave as if tame. How long such "euphoria" lasts is not known. But even in such status the animal is extremely dangerous, as its saliva and excretions still contain the virus.
Monkeys
Monkeys, like humans, can get rabies, however they do not tend to be a common source of rabies. Monkeys with rabies tend to die more quickly than humans. In one study, 9 of 10 monkeys developed severe symptoms or died within 20 days of infection. Rabies is often a concern for individuals travelling to developing countries as monkeys are the most common source of rabies after dogs in these places.
Other small mammals
The most commonly infected terrestrial animals in the U.S.A. are raccoons, skunks, foxes, and coyotes. Any bites by such wild animals must be considered a possible exposure to the rabies virus.
Most cases of rabies in rodents reported to the Centers for Disease Control and Prevention in the U.S.A. have been found among groundhogs (woodchucks). Small rodents such as squirrels, hamsters, guinea pigs, gerbils, chipmunks, rats, and mice and lagomorphs like rabbits and hares are almost never found to be infected with rabies and are not known to transmit rabies to humans.
In the United States, the most commonly reported rabid animal is the domestic cat. In every year since 1990, reported cases of rabies in cats have outnumbered cases of rabies in dogs.
Transport of pet animals between countries
Rabies is endemic to many parts of the world, and one of the reasons given for quarantine periods in international animal transport has been to try to keep the disease out of uninfected regions. However, most developed countries, pioneered by Sweden, now allow unencumbered travel between their territories for pet animals that have demonstrated an adequate immune response to rabies vaccination.
Such countries may limit movement to animals from countries where rabies is considered to be under control in pet animals. There are various lists of such countries. The United Kingdom has developed a list, and France has a rather different list, said to be based on a list of the Office International des Epizooties (OIE). The European Union has a harmonised list. No list of rabies-free countries is readily available from OIE.
In recent years, canine rabies has been practically eliminated in North America and Europe due to extensive and often mandatory vaccination requirements. However it is still a significant problem in parts of Africa, parts of the Middle East, parts of Latin America, and parts of Asia. Dogs are considered to be the main reservoir for rabies in developing countries.
However, the recent spread of rabies in the northeastern United States and further may cause a restrengthening of precautions against movement of possibly rabid animals between developed countries.
See also
- Prevalence of rabies
- Rabies transmission
- Rabies vaccine
- Rabies virus
Footnotes
References
- Baynard, Ashley C. et al. (2011). "Bats and Lyssaviruses." In: Advances in VIRUS RESEARCH VOLUME 79. Research Advances in Rabies. Edited by Alan C. Jackson. Elsevier. ISBN 978-0-12-387040-7.
- Goodwin G. G., and A. M. Greenhall. 1961. "A review of the bats of Trinidad and Tobago." Bulletin of the American Museum of Natural History, 122.
- Joseph Lennox Pawan (1936). "Transmission of the Paralytic Rabies in Trinidad of the Vampire Bat: Desmodus rotundus murinus Wagner, 1840." Annual Tropical Medicine and Parasitol, 30, April 8, 1936, pp. 137â€"156.