A newly found virus capable of causing rabies-like disease in man and animals

Gannoruwa Bat Lyssavirus:



article_image

By Dr Panduka Gunawardena


The researchers of the University of Peradeniya, in collaboration with scientists from the United Kingdom, have recently discovered a novel virus which was subsequently named as Gannoruwa Bat Lyssavirus (GBLV), in the brains of Indian flying foxes, commonly known as Mawavulo or giant fruit bats, in our country. This virus affects the central nervous system mainly the brain, and is capable of causing an invariably fatal nervous disease similar to rabies in humans and other mammals. Rabies is also caused by a lyssavirus and it is a zoonotic disease, meaning that the disease can be transmitted from animals to humans, such as from dogs to humans, commonly by a bite from an infected animal. In the United States, bats are most frequently associated with transmitting rabies to humans. Bat rabies causing human disease and death is also found in Europe and Australia. For humans, rabies is almost invariably fatal if post-exposure prophylaxis is not administered prior to the onset of clinical signs and symptoms. The rabies virus infects the central nervous system, ultimately causing disease in the brain leading to an agonal death.


Rabies is widely distributed across the globe and more than 55,000 people die of rabies each year. Children are the main victims of the disease. Every year, more than 15 million people worldwide receive post-exposure rabies prophylaxis such as vaccination after exposure to the virus to avert the disease – which is estimated to prevent an additional 327,000 rabies deaths. According to World Health Organisation (WHO) about 95 percent of human deaths caused by rabies occur in Asia and Africa. In Asia, more than 4 billion people are at risk of contracting rabies. Of all documented rabies cases, 94% are caused by rabid dog bites. Attacks from other rabid animals, such as cats and wild animals, including bats, are responsible for the remaining 6% of human rabies cases. Rabies is endemic and remains a significant public health problem in Sri Lanka. WHO has categorised Sri Lanka as one of the high risk countries for rabies. In order to control rabies in the country, the government is presently spending a substantial amount of public funds in providing post-exposure prophylaxis which is given free of charge to animal bite victims. Recent estimates indicate that the cost of post-exposure prophylaxis per patient is rupees 25,950 without immunoglobulin. In addition, the government has to bear the cost for vaccination and sterilisation of dogs to prevent spread of the disease.


New virus


The researchers have isolated this disease causing novel virus designated as Gannoruwa Bat Lyssavirus (GBLV), from the brains of the Indian flying foxes (giant fruit bats) that died of a nervous disease similar to rabies. Rabies in man and animals is caused by rabies virus (RABV) which is also another species of lyssavirus. All lyssaviruses are capable of causing rabies-like disease in humans and all mammals including bats. Rabies virus and other lyssaviruses are usually transmitted to susceptible animals, including humans through bites or scratches by the infected animals. Bites and scratches by rabid animals provide direct access of the virus in their saliva to exposed tissue and nerve endings of susceptible animals. After entering the body, the virus is subsequently transported to the central nervous system via the nerve fibres. Exposure to the virus in saliva of the infected animals via mucous membranes such as eyes, nose, mouth and open wounds can also occur. There is no treatment for rabies and other lyssavirus infections. Death is inevitable once clinical signs and symptoms appear. Fortunately, the virus is short lived outside the host and rapidly inactivated by heat, direct sunlight, disinfectants and soap. It lasts up to 24 hours in saliva but less when unprotected and exposed to the elements.


Bats


Bats are a group of mammals capable of flight. There are over 1,000 species of bats in the world and nearly one-fourth of the total number of all mammalian species are bats. In reality, bats are structurally closer to us than many other species of mammals. The skeletal architecture of a bat's wings show essentially the same design as those in human arms and hands. The brains of flying foxes (fruit bats) have more in common with primates – the order to which humans belong, than they do with other groups of mammals. There are 30 species of bats reported in Sri Lanka. The novel virus was discovered in the brains of giant fruit bats or Indian flying foxes (Mawavulo in Sinhala), which are large, fruit eating bats that live in forest, rural and urban areas in many parts of the country. These nocturnal animals roost on big, tall trees with widespread canopies during the daytime and found as large colonies consisting of hundreds to several thousand individuals. They can fly long distances up to 150 kilometres for foraging and have a wide distribution in the South Asian and nearby regions covering Sri Lanka, India, China, Pakistan, Myanmar, Nepal, Bhutan and the Maldives. Although they play an important role in propagating plants and trees by promoting pollination and disperse of seeds, in many countries including Sri Lanka, the fruit bats are often persecuted by the people and bat populations are on the decline as a result of cutting down of roosting trees, shortage of feed and hunting.


Disease in bats


The newly found virus can cause a fatal neurological disease similar to rabies in bats. The bats showing clinical disease caused by GBLV can present with a range of non-specific clinical signs that may include one or more of the followings: inability to fly, eat and drink, overt aggression, spontaneous vocalisation, weakness, tremors, seizures, paralysis, respiratory difficulties and inevitable death. The affected bats are often seen on ground or lower branches in a tree with inability to take off or to fly in normal manner. Although bats are nocturnal animals, the infected bats are frequently found in unusual locations away from their normal roosts during daytime. However, the behaviour or appearance of a bat is not a reliable guide to whether it is infected or not and therefore, all suspicious bats should be considered as potentially infectious.


Disease in man and animals


In latter stages of the disease, the bats infected with GLBV are unable to fly because of paralysis of the wings. They may fall to the ground and often aggressively bite into any object live or otherwise that they come across before their inevitable death.


These grounded bats pose a potential threat to their handlers and other animals such as dogs that prey on them. Particularly, children need to be taught never to handle injured or grounded live bats. The bat virus transmitting into humans through carnivorous animals particularly through dogs is a strong possibility. Free roaming dogs that get bitten by grounded GBLV infected bats can develop the disease and they in turn may transmit the disease to humans and other animals.


It is also presumed that, if an animal of a non-bat species develops clinical disease due to GBLV infection, that animal has the potential to transmit GBLV to humans and other mammals. The incubation period, can vary from days to years and death occurs after a short illness of progressive, severe nervous signs. All bat species are considered potentially infectious.


Potential Risk


People are at risk of contracting GBLV if they handle bats without proper precautions. Rabies virus and other lyssaviruses are usually transmitted to humans via bites or scratches. This provides direct access of the virus in saliva to exposed tissue and nerve endings of the victims. Exposure to virus in bat saliva via mucous membranes such as eyes, nose, mouth and open wounds is also possible. This type of virus transmission may occur in bat infested caves. Although the principal mode of lyssavirus transmission occurs via bites, the animals feeding on infected carcasses can also contract the disease. Scavenging of dead bats is a potential means through which carnivores can contract rabies and other lyssavirus infections. The possibility of bat carcasses being scavenged by wild and domestic carnivores is high in suburban areas where human and pet contact with wildlife may be greater.


The findings of the researchers indicate that fruit bats are a reservoir-vector for lyssaviruses that harbour and transmit the virus, not only in Sri Lanka but also in the Indian subcontinent and nearby regions. The bats are widespread in the region and occasionally come in contact with humans and domestic animals such as dogs, which provides opportunities for virus spill over. Domestic pets, particularly dogs or cats, coming into close physical contact with bats through chasing and catching bats and/or ingestion of bats is possible. This close contact forms a risk of transmission of GBLV to dogs and cats and possibly, to their owners.


This adds another dimension to the control of rabies and other lyssavirus infections in the south Asian region. Therefore, control of free-roaming dog population and use of rabies vaccines that are effective against GBLV are important. Prevention of pets and other domestic animals from coming into contact with bats is also an effective measure. This may include keeping dogs and cats inside at night, particularly when bats are feeding on fruiting or flowering trees on our property. There is no known risk of contracting lyssavirus infection from bats flying overhead, contact with bat urine, faeces or blood. Although there is no evidence to suggest lyssavirus could be contracted by eating fruits partially eaten by a bat, any fruit that has been partially eaten by any animal should not be eaten as it could be contaminated by a variety of other disease causing germs. GBLV infection is more common in sick, injured or orphaned bats. Domestic animals, including livestock, elephants, dogs and other pets may potentially be exposed to GBLV through contact with bats.


Categories of risk


Bats can be categorised based on their potential to transmit GBLV to humans and other mammals including potential for an infected bat to have infectious contact with a human or other mammal. These categories are listed from highest to lowest based on urgency for action:


Category 3 – high human health risk. Bats that are known or reasonably suspected to have had potentially infectious contact with a human for instance, a bat has bitten or scratched a person. Within Category 3, bats with clinical signs suggestive of GBLV are of highest risk.


Category 2 – high animal health risk, medium human health risk. This category includes bats that pose a potential risk of infection to humans. Disease investigation and exclusion testing is recommended either due to history or clinical signs suggestive of GBLV without a history of a potentially infectious contact with a human (Category 2a), or history of known or suspected contact with another animal which has potentially exposed to GBLV via bats (Category 2b).


Category 1 – low risk. Bats that are neither Category 2 nor Category 3 —Bats that have no history of known or suspected contact with another animal or person and for which the level of suspicion for GBLV infection is low such as no clinical signs consistent with GBLV infection.


Handling a live bat


Members of the public are strongly advised not to attempt to handle an injured, unwell or aggressive bat. If you come across a lone bat or an injured, sick or orphaned bat, do not touch it. Avoid contact with all species of live bats. Only vaccinated people should handle live bats. Emergency treatment is necessary if bitten or scratched by a bat. Proper cleansing of the wound is the single most effective measure for reducing transmission of the virus. However, do not scrub the wound. The wound should be immediately washed with soap and water for at least 5 minutes. An antiseptic with anti-viral action, such as household disinfectants or alcohol (ethanol) should be applied after washing. If saliva enters the eyes, nose or mouth, the area should be flushed thoroughly with water. Contact your Doctor or nearest hospital as early as possible and seek medical advice about pre-exposure vaccination. Contact your local veterinarian if you suspect that your pet might have been bitten or scratched by a bat.


Handling a dead bat


If the bat is dead, it should be collected and placed inside a secure and waterproof container. Exposure of skin or mucous membranes to the secretions or excretions of the bat must be avoided. Handling the carcass remotely for example using a garden spade or other implement, inverting a thick plastic bag over the carcass, and using rubber gloves are recommended methods of preventing direct exposure.


In light of this new discovery, the general public is advised to take necessary precautions against the potential danger from GBLV infection transmitted through bats. Human health should be an overriding factor in managing all incidents involving potential GBLV infection of pet animals and their owners. Greater public awareness is needed regarding the need to submit suspected rabid animals including bats for diagnostic evaluation. Moreover, the governmental and non-governmental institutions involved in rabies control activities in the country need to address this problem in their programmes. A case in point is the death of a French child due to rabies recently in France, a country free of the disease. The child had contracted the disease while holidaying in Sri Lanka and this incident drew world-wide attention including the international tourism sector on rabies situation in the island.


More information on this novel virus designated as Gannoruwa Bat Lyssavirus can be found in the article "Lyssavirus in Indian Flying Foxes, Sri Lanka" published in the Emerging Infectious Diseases journal. This article can be accessed through the following link.


http://wwwnc.cdc.gov/eid/article/22/8/pdfs/15-1986.pdf


 
 
 
 
 
 
 
 
 
 
animated gif
Processing Request
Please Wait...