PROMEDHYBRID MOSQUITOES AND WEST NILE VIRUSSat Mar 6 15:06:42 200464.140.159.10-------- Original Message --------Subject: PRO> Hybrid mosquitoes and West Nile virusDate: Sat, 6 Mar 2004 12:57:48 -0500 (EST)From: owner-promed@promed.isid.harvard.edu Reply-To: promed@promed.isid.harvard.edu To: promed@promedmail.org HYBRID MOSQUITOES AND WEST NILE VIRUS*************************************A ProMED-mail post http://www.promedmail.org/ ProMED mail is a program of theInternational Society for Infectious Diseases http://www.isid.org />Date: 5 March 2004From: ProMED-mail Source: Scripps Howard News Service 03/04/2004 [edited] http://www.knoxstudio.com/shns/?action=detail&pk=WESTNILE-03-04-04 _Culex pipiens_ and _Culex molestus_ hybrids in the USA---------------------------------------------------West Nile virus has set up housekeeping in the United States so readily because of a hybrid mosquito species (_Culex pipiens_ s.s. X _Culex pipiens_ form _molestus_) that transmits the disease by biting both people and birds.But the disease has not taken hold in northern Europe, where the infection is limited mainly to bird-biters (_Cx. pipiens_), a new study suggests.The first case of West Nile virus detected in the Western Hemisphere was in the New York City area, in 1999. Since then, the virus has spread to infect humans in 45 states, although 4 of 5 people who become infected have no symptoms. But for the rest, the virus dishes out a flu-like illness that can spread to the brain, with fatal effects.The virus is not typically transmitted between humans, although the federal Centers for Disease Control and Prevention has reported a single case of mother-to-infant infection and a second transmission to a breastfed child.Most of the time, "you must have a mosquito that bites a bird today and a human tomorrow for transmission to occur," said Dina Fonseca, a genetic researcher with the Smithsonian Institution's Museum of Natural History. She is the lead author of the new study, published Friday in the journal Science.Humans and other mammals don't seem to carry enough of the virus in their blood to pass it along to birds or other animals through mosquitoes, "so if you have a mosquito that only bites mammals, there is no transmission to humans," Fonseca said.Fonseca and Richard Wilkinson, of the Walter Reed Army Research Institute in Silver Spring, MD, collaborated with other scientists around the world to study the genetic makeup of the _Cx. pipiens_ complex of mosquitoes, which is strongly linked to the West Nile outbreak in the United States.The scientists analyzed mosquito samples from 33 locations in various countries, including Australia, Great Britain, Germany, Italy, Japan, Jordan and the United States. The researchers found that there are 2 different forms of the same species residing in northern Europe that tend to bite either birds or humans but not both. The people-biting form lives underground, in places such as subways and basements, while the form that bites birds lives in the open.Although the 2 groups live in the same areas and appear morphologically identical, the analysis showed that the northern European _Culex pipiens_ s.s. mosquitoes are not swapping with the closely related _Culex pipiens_ form _molestus_ DNA in some key regions.But among the US samples, 40 per cent of the _Culex_ mosquitoes were hybrids. In southern Europe, where outbreaks of West Nile are somewhat more common, about 10 per cent of the mosquitoes were hybrids.Among _Culex_ mosquitoes in Japan, Australia, and the Middle East, the distinction between above- and below-ground populations doesn't appear to exist, the researchers said. The findings make sense to other scientists who have tried to understand how _Culex pipiens_ that had long been considered a bird-biter seemed to be a key factor in spreading the disease to humans in many places."It appears that what we've been calling pipiens are hybrids," Larry Kramer, Director of the insect virus lab at the New York state Department of Health, told _Science_. "It fits with what we've been seeing."But the CDC reports that at least 43 species of mosquitoes around the United States are infected with West Nile, including several others known to bite humans.Many other public health experts think West Nile spread so rapidly across the United States, and also much of Canada, because the virus is new to the Americas and neither birds nor other animals, including humans, had any immunity to it, while Europeans have been exposed to it for centuries.But Fonseca said it's clear that the existence of so many infected hybrid mosquitoes in the United States points to a different pattern of natural hosts and a difference in infection rates. "It's not the only reason, but it could be a component of this difference," Fonseca said.On the Net: http://www.sciencemag.org > http://www.cdc.gov/ncidod/dvbid/westnile/site!26index.htm [byline: Lee Bowman]--ProMED-mail promed@promedmail.org [West Nile virus is unusual in seeming to be transmitted by so many different mosquito species; at least 43 species in 10 genera have been found positive for WN virus in the USA since 1999. The virus can also infect ornithophagic ticks (_Argas hermanni_ and _Hyalomma asiaticum_ ), but their role in the epidemiology of WN remains unclear. Nevertheless it appears that _Culex_ species, in particular _Cx. pipiens_, are the principal vectors in the USA. Elsewhere, such as in Europe and Africa, _Culex_ mosquitoes are the main vectors, including some species that provide a bridge by biting both birds and humans.The publication by Dina M Fonseca,_et al, Emerging vectors in the _Culex pipiens_ complex (Science 2004; 303: 15535-8, on which the above news report is based, will undoubtedly generate much interest amongst virologists, and I would guess also considerable controversy as to whether hybridization in the _Cx. pipiens_ complex explains, or helps explain, how WN has spread so rapidly in the USA.Another recent and relevant publication is by S Higgs, K Snow, and EA Gould, "The potential for West Nile virus to establish outside of its natural range: a consideration of potential mosquito vectors in the United Kingdom" (Transactions of the Royal Society of Tropical Medicine and Hygiene 2004; 98; 82-7. - Mod.MS][see also:West Nile virus, human death - USA (NC) 20040224.0583West Nile virus, bird - USA (Texas) 20040212.04642003---West Nile virus update 2003 - Canada (05) 20030504.1115West Nile virus update 2003 - Canada (03): correction 20030429.1060West Nile virus update 2003 - Canada (02) 20030428.10462002----West Nile virus, humans - USA (VT, MT ex OH): prob. 20020911.5281West Nile virus, birds - Mexico (Yucatan): suspected 20020828.5172West Nile virus & weather 20020807.4984West Nile virus update 2002 - USA (14) 20020801.4911West Nile virus - USA 2001: final report 20020613.4491West Nile virus, mosquitoes - Israel (02) 20020520.4276West Nile virus review papers online 20020304.36832001---West Nile virus surveillance 2001 - USA (NYC) 20011213.3017West Nile virus, mosquitoes - USA: update 20010925.2339West Nile virus, mosquitoes - USA (Massachusetts) 20010831.2068West Nile virus surveillance 2001 - USA (18) 20010825.2017West Nile virus surveillance 2001 - USA (17) 20010817.1946West Nile virus surveillance 2001 - USA (16) 20010810.1890West Nile virus surveillance 2001 - USA (15) 20010804.1532West Nile virus - Romania (Bucharest) 20010731.1499]............ms/pg/sh_________________________________________________________________It's fast, it's easy and it's free. Get MSN Messenger today! http://www.msn.co.uk/messenger *##########################################################*ProMED-mail makes every effort to verify the reports thatare posted, but the accuracy and completeness of theinformation, and of any statements or opinions basedthereon, are not guaranteed. The reader assumes all risks inusing information posted or archived by ProMED-mail. ISIDand its associated service providers shall not be heldresponsible for errors or omissions or held liable for anydamages incurred as a result of use or reliance upon postedor archived material.************************************************************Visit ProMED-mail's web site at http://www.promedmail.org >.Send all items for posting to: promed@promedmail.org (NOT to an individual moderator). If you do not give yourfull name and affiliation, it may not be posted. Sendcommands to subscribe/unsubscribe, get archives, help,etc. to: majordomo@promedmail.org . 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To: promed@promedmail.org HYBRID MOSQUITOES AND WEST NILE VIRUS*************************************A ProMED-mail post http://www.promedmail.org/ ProMED mail is a program of theInternational Society for Infectious Diseases http://www.isid.org />Date: 5 March 2004From: ProMED-mail Source: Scripps Howard News Service 03/04/2004 [edited] http://www.knoxstudio.com/shns/?action=detail&pk=WESTNILE-03-04-04 _Culex pipiens_ and _Culex molestus_ hybrids in the USA---------------------------------------------------West Nile virus has set up housekeeping in the United States so readily because of a hybrid mosquito species (_Culex pipiens_ s.s. X _Culex pipiens_ form _molestus_) that transmits the disease by biting both people and birds.But the disease has not taken hold in northern Europe, where the infection is limited mainly to bird-biters (_Cx. pipiens_), a new study suggests.The first case of West Nile virus detected in the Western Hemisphere was in the New York City area, in 1999. Since then, the virus has spread to infect humans in 45 states, although 4 of 5 people who become infected have no symptoms. But for the rest, the virus dishes out a flu-like illness that can spread to the brain, with fatal effects.The virus is not typically transmitted between humans, although the federal Centers for Disease Control and Prevention has reported a single case of mother-to-infant infection and a second transmission to a breastfed child.Most of the time, "you must have a mosquito that bites a bird today and a human tomorrow for transmission to occur," said Dina Fonseca, a genetic researcher with the Smithsonian Institution's Museum of Natural History. She is the lead author of the new study, published Friday in the journal Science.Humans and other mammals don't seem to carry enough of the virus in their blood to pass it along to birds or other animals through mosquitoes, "so if you have a mosquito that only bites mammals, there is no transmission to humans," Fonseca said.Fonseca and Richard Wilkinson, of the Walter Reed Army Research Institute in Silver Spring, MD, collaborated with other scientists around the world to study the genetic makeup of the _Cx. pipiens_ complex of mosquitoes, which is strongly linked to the West Nile outbreak in the United States.The scientists analyzed mosquito samples from 33 locations in various countries, including Australia, Great Britain, Germany, Italy, Japan, Jordan and the United States. The researchers found that there are 2 different forms of the same species residing in northern Europe that tend to bite either birds or humans but not both. The people-biting form lives underground, in places such as subways and basements, while the form that bites birds lives in the open.Although the 2 groups live in the same areas and appear morphologically identical, the analysis showed that the northern European _Culex pipiens_ s.s. mosquitoes are not swapping with the closely related _Culex pipiens_ form _molestus_ DNA in some key regions.But among the US samples, 40 per cent of the _Culex_ mosquitoes were hybrids. In southern Europe, where outbreaks of West Nile are somewhat more common, about 10 per cent of the mosquitoes were hybrids.Among _Culex_ mosquitoes in Japan, Australia, and the Middle East, the distinction between above- and below-ground populations doesn't appear to exist, the researchers said. The findings make sense to other scientists who have tried to understand how _Culex pipiens_ that had long been considered a bird-biter seemed to be a key factor in spreading the disease to humans in many places."It appears that what we've been calling pipiens are hybrids," Larry Kramer, Director of the insect virus lab at the New York state Department of Health, told _Science_. "It fits with what we've been seeing."But the CDC reports that at least 43 species of mosquitoes around the United States are infected with West Nile, including several others known to bite humans.Many other public health experts think West Nile spread so rapidly across the United States, and also much of Canada, because the virus is new to the Americas and neither birds nor other animals, including humans, had any immunity to it, while Europeans have been exposed to it for centuries.But Fonseca said it's clear that the existence of so many infected hybrid mosquitoes in the United States points to a different pattern of natural hosts and a difference in infection rates. "It's not the only reason, but it could be a component of this difference," Fonseca said.On the Net: http://www.sciencemag.org > http://www.cdc.gov/ncidod/dvbid/westnile/site!26index.htm [byline: Lee Bowman]--ProMED-mail promed@promedmail.org [West Nile virus is unusual in seeming to be transmitted by so many different mosquito species; at least 43 species in 10 genera have been found positive for WN virus in the USA since 1999. The virus can also infect ornithophagic ticks (_Argas hermanni_ and _Hyalomma asiaticum_ ), but their role in the epidemiology of WN remains unclear. Nevertheless it appears that _Culex_ species, in particular _Cx. pipiens_, are the principal vectors in the USA. Elsewhere, such as in Europe and Africa, _Culex_ mosquitoes are the main vectors, including some species that provide a bridge by biting both birds and humans.The publication by Dina M Fonseca,_et al, Emerging vectors in the _Culex pipiens_ complex (Science 2004; 303: 15535-8, on which the above news report is based, will undoubtedly generate much interest amongst virologists, and I would guess also considerable controversy as to whether hybridization in the _Cx. pipiens_ complex explains, or helps explain, how WN has spread so rapidly in the USA.Another recent and relevant publication is by S Higgs, K Snow, and EA Gould, "The potential for West Nile virus to establish outside of its natural range: a consideration of potential mosquito vectors in the United Kingdom" (Transactions of the Royal Society of Tropical Medicine and Hygiene 2004; 98; 82-7. - Mod.MS][see also:West Nile virus, human death - USA (NC) 20040224.0583West Nile virus, bird - USA (Texas) 20040212.04642003---West Nile virus update 2003 - Canada (05) 20030504.1115West Nile virus update 2003 - Canada (03): correction 20030429.1060West Nile virus update 2003 - Canada (02) 20030428.10462002----West Nile virus, humans - USA (VT, MT ex OH): prob. 20020911.5281West Nile virus, birds - Mexico (Yucatan): suspected 20020828.5172West Nile virus & weather 20020807.4984West Nile virus update 2002 - USA (14) 20020801.4911West Nile virus - USA 2001: final report 20020613.4491West Nile virus, mosquitoes - Israel (02) 20020520.4276West Nile virus review papers online 20020304.36832001---West Nile virus surveillance 2001 - USA (NYC) 20011213.3017West Nile virus, mosquitoes - USA: update 20010925.2339West Nile virus, mosquitoes - USA (Massachusetts) 20010831.2068West Nile virus surveillance 2001 - USA (18) 20010825.2017West Nile virus surveillance 2001 - USA (17) 20010817.1946West Nile virus surveillance 2001 - USA (16) 20010810.1890West Nile virus surveillance 2001 - USA (15) 20010804.1532West Nile virus - Romania (Bucharest) 20010731.1499]............ms/pg/sh_________________________________________________________________It's fast, it's easy and it's free. Get MSN Messenger today! http://www.msn.co.uk/messenger *##########################################################*ProMED-mail makes every effort to verify the reports thatare posted, but the accuracy and completeness of theinformation, and of any statements or opinions basedthereon, are not guaranteed. The reader assumes all risks inusing information posted or archived by ProMED-mail. ISIDand its associated service providers shall not be heldresponsible for errors or omissions or held liable for anydamages incurred as a result of use or reliance upon postedor archived material.************************************************************Visit ProMED-mail's web site at http://www.promedmail.org >.Send all items for posting to: promed@promedmail.org (NOT to an individual moderator). If you do not give yourfull name and affiliation, it may not be posted. Sendcommands to subscribe/unsubscribe, get archives, help,etc. to: majordomo@promedmail.org . For assistance from ahuman being send mail to: owner-promed@promedmail.org. ############################################################
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