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Bats and the emerging threat of rabies
Newsdesk Bats and the emerging threat of rabies
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protection against rabies. But in most cases of rabies acquired from bats, Mahy explains, “there is no clear
Robert Harding Picture Library
Rabies, an age-old infection historically associated with dogs, is emerging as a zoonosis originating in bats. “Bat rabies has been fully appreciated only in the past 50 years, and new bat lyssaviruses are still being identified”, says Charles Rupprecht, of the Centers for Disease Control and Prevention (CDC; Atlanta, GA, USA). The two most recently discovered are the Irkut and West Caucasian bat (WBC) viruses isolated from bats in Russia in 2002 (Emerg Infect Dis 2003; 9: 1623–25). Phylogenetic studies by scientists at the Institut Pasteur (Paris, France) suggest that rabies, far from being primarily a canine infection, evolved in insectivorous bats (Chiroptera spp) long before it emerged in carnivores 900–1500 years ago—most likely as virus “spillover” from its original hosts. Bats have been identified as reservoirs of lyssaviruses on all continents except Antarctica. “Given bat mobility, no major geographic area can be considered truly free from lyssaviruses”, says Rupprecht. “Publichealth officials need to be aware of the potential of bats to transmit lyssaviruses and to increase surveillance and public education.” Seven lyssavirus genotypes are known, including classic rabies virus (genotype 1), and all have been isolated from bats. Human rabies must now be regarded as a clinical diagnosis only, since all lyssaviruses cause fatal disease that is clinically indistinguishable from classic rabies. And bat lyssaviruses have killed people in so-called rabiesfree countries—Australia (two deaths in 1996 and 1998) and the UK (one death in 2002). “In the USA, most human rabies is caused by bat variants, even though bat rabies represents only 8% of animal rabies cases”, says Brian Mahy of CDC. In the past 20 years rabies has spread throughout the raccoon population of the eastern USA, yet only one person has died of raccoonacquired rabies (in Virginia in 2003), compared with at least 31 deaths from bat rabies. Post-exposure prophylaxis (PEP) with rabies vaccine and immune globulin is the single most important
Rabies may first have evolved in bats
history of contact with bats, and often we do not know how the virus gains entry”. Rupprecht suggests that many people may not be aware that a bat bite is a risk for rabies transmission and therefore fail to report it. Australian bat lyssavirus, first isolated in 1996 from a fruit bat (flying fox, Pteropus spp) and now widespread in all Australian bat species, is closely related to classic rabies virus. “In 1996 bat handlers and wildlife workers were confronted with a previously unknown disease”, recalls John Scott (Queensland Health, Brisbane, Australia). “With no readily available test to confirm exposure before clinical illness developed, thousands of doses of prophylactic rabies vaccine and immune globulin were distributed.” Potentially avoidable bat bites and scratches continued to be reported, so that “post-exposure prophylaxis was needed when simple preventive measures would have been more appropriate”. The lyssaviruses that infect American bats (both insectivorous and South American vampire) are variants of classic rabies virus, and treatment after suspected exposure is
with traditional rabies PEP, as it is for exposure to the closely related Australian bat lyssavirus. But there are concerns that commercial biologicals may not be effective against more distantly related lyssaviruses. “In laboratory rodents the protective ability of pre-exposure rabies vaccination against Irkut, WBC, and two lyssaviruses from central Asia was substantially reduced, and conventional rabies post-exposure prophylaxis with vaccine and immune globulin failed”, says CDC’s Cathleen Hanlon. “In general, protection was inversely related to the genetic distance between the new isolates and traditional rabies virus, with WBC the most divergent.” This makes avoidance of exposure and the use of protective equipment such as gloves when handling bats all the more important. The burden of bat rabies pales into insignificance when compared with canine rabies, which is still the major lyssavirus infection in India, Asia, and Africa. “Mass immunisation of dogs has been successful in South America”, notes Hilary Koprowski (Thomas Jefferson University, Philadelphia, PA, USA), “but it is lagging far behind in southeast Asia, where the largest number of human rabies cases occurs every year”. Estimates put the number of human rabies cases worldwide at 55 000–70 000 annually, and more than 5 million PEPs are given each year. New vaccines and antibodies are needed for protection against classic rabies as well as new lyssaviruses. “Tissue-culture vaccines are highly effective but expensive”, says Rupprecht, “and the nerve-tissue vaccines widely used in developing countries are less effective and may cause serious adverse events”. There is a worldwide shortage of rabies immune globulin, but antibodies from transgenic tobacco plants, developed by Koprowski, promise to meet future needs. These antibodies, he claims, are “as good as the antibody produced in animal cells, safer, and less expensive to produce”. Dorothy Bonn
THE LANCET Infectious Diseases Vol 4 January 2004
http://infection.thelancet.com
For personal use. Only reproduce with permission from The Lancet.
8
protection against rabies. But in most cases of rabies acquired from bats, Mahy explains, “there is no clear
Robert Harding Picture Library
Rabies, an age-old infection historically associated with dogs, is emerging as a zoonosis originating in bats. “Bat rabies has been fully appreciated only in the past 50 years, and new bat lyssaviruses are still being identified”, says Charles Rupprecht, of the Centers for Disease Control and Prevention (CDC; Atlanta, GA, USA). The two most recently discovered are the Irkut and West Caucasian bat (WBC) viruses isolated from bats in Russia in 2002 (Emerg Infect Dis 2003; 9: 1623–25). Phylogenetic studies by scientists at the Institut Pasteur (Paris, France) suggest that rabies, far from being primarily a canine infection, evolved in insectivorous bats (Chiroptera spp) long before it emerged in carnivores 900–1500 years ago—most likely as virus “spillover” from its original hosts. Bats have been identified as reservoirs of lyssaviruses on all continents except Antarctica. “Given bat mobility, no major geographic area can be considered truly free from lyssaviruses”, says Rupprecht. “Publichealth officials need to be aware of the potential of bats to transmit lyssaviruses and to increase surveillance and public education.” Seven lyssavirus genotypes are known, including classic rabies virus (genotype 1), and all have been isolated from bats. Human rabies must now be regarded as a clinical diagnosis only, since all lyssaviruses cause fatal disease that is clinically indistinguishable from classic rabies. And bat lyssaviruses have killed people in so-called rabiesfree countries—Australia (two deaths in 1996 and 1998) and the UK (one death in 2002). “In the USA, most human rabies is caused by bat variants, even though bat rabies represents only 8% of animal rabies cases”, says Brian Mahy of CDC. In the past 20 years rabies has spread throughout the raccoon population of the eastern USA, yet only one person has died of raccoonacquired rabies (in Virginia in 2003), compared with at least 31 deaths from bat rabies. Post-exposure prophylaxis (PEP) with rabies vaccine and immune globulin is the single most important
Rabies may first have evolved in bats
history of contact with bats, and often we do not know how the virus gains entry”. Rupprecht suggests that many people may not be aware that a bat bite is a risk for rabies transmission and therefore fail to report it. Australian bat lyssavirus, first isolated in 1996 from a fruit bat (flying fox, Pteropus spp) and now widespread in all Australian bat species, is closely related to classic rabies virus. “In 1996 bat handlers and wildlife workers were confronted with a previously unknown disease”, recalls John Scott (Queensland Health, Brisbane, Australia). “With no readily available test to confirm exposure before clinical illness developed, thousands of doses of prophylactic rabies vaccine and immune globulin were distributed.” Potentially avoidable bat bites and scratches continued to be reported, so that “post-exposure prophylaxis was needed when simple preventive measures would have been more appropriate”. The lyssaviruses that infect American bats (both insectivorous and South American vampire) are variants of classic rabies virus, and treatment after suspected exposure is
with traditional rabies PEP, as it is for exposure to the closely related Australian bat lyssavirus. But there are concerns that commercial biologicals may not be effective against more distantly related lyssaviruses. “In laboratory rodents the protective ability of pre-exposure rabies vaccination against Irkut, WBC, and two lyssaviruses from central Asia was substantially reduced, and conventional rabies post-exposure prophylaxis with vaccine and immune globulin failed”, says CDC’s Cathleen Hanlon. “In general, protection was inversely related to the genetic distance between the new isolates and traditional rabies virus, with WBC the most divergent.” This makes avoidance of exposure and the use of protective equipment such as gloves when handling bats all the more important. The burden of bat rabies pales into insignificance when compared with canine rabies, which is still the major lyssavirus infection in India, Asia, and Africa. “Mass immunisation of dogs has been successful in South America”, notes Hilary Koprowski (Thomas Jefferson University, Philadelphia, PA, USA), “but it is lagging far behind in southeast Asia, where the largest number of human rabies cases occurs every year”. Estimates put the number of human rabies cases worldwide at 55 000–70 000 annually, and more than 5 million PEPs are given each year. New vaccines and antibodies are needed for protection against classic rabies as well as new lyssaviruses. “Tissue-culture vaccines are highly effective but expensive”, says Rupprecht, “and the nerve-tissue vaccines widely used in developing countries are less effective and may cause serious adverse events”. There is a worldwide shortage of rabies immune globulin, but antibodies from transgenic tobacco plants, developed by Koprowski, promise to meet future needs. These antibodies, he claims, are “as good as the antibody produced in animal cells, safer, and less expensive to produce”. Dorothy Bonn
THE LANCET Infectious Diseases Vol 4 January 2004
http://infection.thelancet.com
For personal use. Only reproduce with permission from The Lancet.