West nile virus pathophysiology: Difference between revisions

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==Overview==
==Overview==


==Pathogenesis==
==West Nile virus pathophysiology==
===Transmission===
===Transmission===
The West Nile Virus is transmitted by the bite of a mosquito.  Its life-cycle is based on a "bird-mosquito-bird transmission". Although the virus may have 65 species of mosquitos as natural hosts, only a few of those are capable of transmitting the virus among birds and humans. Those responsible for the viral transmission belong to different families, depending of the region of the US:<ref name="pmid23860989">{{cite journal| author=Petersen LR, Brault AC, Nasci RS| title=West Nile virus: review of the literature. | journal=JAMA | year= 2013 | volume= 310 | issue= 3 | pages= 308-15 | pmid=23860989 | doi=10.1001/jama.2013.8042 | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=23860989 }} </ref>
Birds are the main reservoir of West Nile virus (WNV), but transmission of the virus is by mosquito bite of an infected bird with high-level viremia, such as birds of the family ''Passeriformes''.<ref name=CDC>{{cite web | title = Emerging Infectious Diseases | url = http://wwwnc.cdc.gov/eid/article/9/3/02-0628_article }}</ref> Thus, transmission is frequently denoted as "bird-mosquito-bird" transmission. Although direct bird-to-bird transmission has been speculated, further validation is still required.<ref name="pmid12643825">{{cite journal| author=Komar N, Langevin S, Hinten S, Nemeth N, Edwards E, Hettler D et al.| title=Experimental infection of North American birds with the New York 1999 strain of West Nile virus. | journal=Emerg Infect Dis | year= 2003 | volume= 9 | issue= 3 | pages= 311-22 | pmid=12643825 | doi=10.3201/eid0903.020628 | pmc=PMC2958552 | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=12643825  }} </ref> Other species may also be infected, such as horses, cats, and dogs. Humans are considered dead-end hosts because the disease rarely progresses to viremia in humans, making transmission of the virus from a human unlikely except in some reported cases of transmission by blood transfusion, breastfeeding, or organ transplantation.<ref name="pmid12773646">{{cite journal| author=Iwamoto M, Jernigan DB, Guasch A, Trepka MJ, Blackmore CG, Hellinger WC et al.| title=Transmission of West Nile virus from an organ donor to four transplant recipients. | journal=N Engl J Med | year= 2003 | volume= 348 | issue= 22 | pages= 2196-203 | pmid=12773646 | doi=10.1056/NEJMoa022987 | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=12773646  }} </ref><ref name="pmid14500806">{{cite journal| author=Pealer LN, Marfin AA, Petersen LR, Lanciotti RS, Page PL, Stramer SL et al.| title=Transmission of West Nile virus through blood transfusion in the United States in 2002. | journal=N Engl J Med | year= 2003 | volume= 349 | issue= 13 | pages= 1236-45 | pmid=14500806 | doi=10.1056/NEJMoa030969 | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=14500806 }} </ref><ref name="pmid12375687">{{cite journal| author=Centers for Disease Control and Prevention (CDC)| title=Possible West Nile virus transmission to an infant through breast-feeding--Michigan, 2002. | journal=MMWR Morb Mortal Wkly Rep | year= 2002 | volume= 51 | issue= 39 | pages= 877-8 | pmid=12375687 | doi= | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=12375687  }} </ref>
* Northern half of the United States - ''Culex pipiens''
* Southern states - ''Culex quinquefasciatus''
* Western states and overlapping areas of distribution of ''Culex pipiens'' and ''Culex quinquefasciatus'' - ''Culex tarsal is''


Some birds behave as '''amplifier hosts'''.  Particularly those of the order ''Passeriformes'', develop high viral loads, that infect mosquitos that feed upod their blood.<ref name=CDC>{{cite web | title = Emerging Infectious Diseases | url = http://wwwnc.cdc.gov/eid/article/9/3/02-0628_article }}</ref>  Humans, on the other hand, behave as '''dead-end hosts''' since they do not develop high-level serum [[viremia]]s to infect mosquitoes.<ref name="pmid20874087">{{cite journal| author=Zou S, Foster GA, Dodd RY, Petersen LR, Stramer SL| title=West Nile fever characteristics among viremic persons identified through blood donor screening. | journal=J Infect Dis | year= 2010 | volume= 202 | issue= 9 | pages= 1354-61 | pmid=20874087 | doi=10.1086/656602 | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=20874087  }} </ref><ref name="pmid14500806">{{cite journal| author=Pealer LN, Marfin AA, Petersen LR, Lanciotti RS, Page PL, Stramer SL et al.| title=Transmission of West Nile virus through blood transfusion in the United States in 2002. | journal=N Engl J Med | year= 2003 | volume= 349 | issue= 13 | pages= 1236-45 | pmid=14500806 | doi=10.1056/NEJMoa030969 | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=14500806  }} </ref>


==Pathophysiology==
Mosquitoes responsible for viral transmission belong to different families, varying based on geographical location:<ref name="pmid23860989">{{cite journal| author=Petersen LR, Brault AC, Nasci RS| title=West Nile virus: review of the literature. | journal=JAMA | year= 2013 | volume= 310 | issue= 3 | pages= 308-15 | pmid=23860989 | doi=10.1001/jama.2013.8042 | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=23860989  }} </ref>
WNV is a member of the family Flaviviridae (genus Flavivirus). Serologically, it is a member of the Japanese encephalitis virus antigenic complex, which includes St. Louis, Japanese, Kunjin, and Murray Valley encephalitis viruses. WNV was first isolated in the WN province of Uganda in 1937. Human and equine outbreaks have been recorded in portions of Africa, southern
* ''Culex pipiens'': Northern half and West of USA
Europe, North America, and Asia. Although it is still not known when or how WNV was introduced into North America, international travel of infected persons to New York, importation of infected birds or mosquitoes, or migration of infected birds are all possibilities.
* ''Culex quinquefasciatus'': Southeast and West of USA
[http://www.cdc.gov/ncidod/dvbid/westnile/resources/wnv-guidelines-aug-2003.pdf]
* ''Culex tarsal'': West of USA
The virus is transmitted through mosquito vectors, which bite and infect birds. The birds are amplifying hosts, developing sufficient viral levels to transmit the infection to other biting mosquitoes which go on to infect other birds (in the [[Western hemisphere]] the [[American robin]] and the [[American crow]] are the most common carriers) and also humans. The infected mosquito species vary according to geographical area; in the US ''Culex pipiens'' (Eastern US), ''Culex tarsalis'' (Midwest and West), and ''Culex quinquefasciatus'' (Southeast) are the main sources.<ref>Hayes E B, Komar N, Nasci R S, Montgomery S P, Oleary D R, Campbell G L. "Epidemiology and transmission dynamics of West Nile virus disease." ''Emerging Infectious Diseases Journal'' 2005a; 11: 1167-1173</ref>


In mammals the virus does not multiply as readily, and it is believed that mosquitoes biting infected mammals do not further transmit the virus,<ref>Taylor R M, Hurlbut H S, Dressler H R, Spangler E W, Thrasher D. "Isolation of West Nile virus from ''Culex'' mosquitoes." ''Journal of the Egyptian Medical Association'' 1953; 36: 199-208</ref> making mammals so-called dead-end infections.
==Pathogenesis==
 
Following inoculation, replication of WNV takes place in Langerhans epidermal dendritic cells, which are antigen-presenting immune cells.(26) These cells then migrate to lymph nodes, resulting in lymph node drainage, followed by viremia and dissemination of the virus into other organs, namely the spleen and the kidneys. Within one week, the virus is successfully cleared from serum and tissue compartments among immunocompetent individuals.  
A 2004 paper in ''Science'' found that ''Culex pipiens'' mosquitoes existed in two populations in [[Europe]], one which bites birds and one which bites humans. In North America 40% of ''Culex pipiens'' were found to be hybrids of the two types which bite both birds and humans, providing a vector for West Nile virus. This is thought to provide an explanation of why the West Nile disease has spread more quickly in North America than Europe.
 
It was initially believed that direct human-to-human transmission was only caused by occupational exposure,<ref>CDC. "Laboratory-acquired West Nile virus infections - United States,2002." ''MMWR'' 2002c; 51: 1133-1135.</ref> or conjunctival exposure to infected blood.<ref>Fonseca K, Prince G D, Bratvold J, Fox J D, Pybus M, Preksaitis J K, Tilley P. "West Nile virus infection and conjunctival exposure." ''Emerging Infectious Diseases Journal'' 3005; 11: 1648-1649.</ref> The US outbreak revealed novel transmission methods, through blood transfusion,<ref>CDC. "Investigation of blood transfusion recipients with West Nile virus infections." ''MMWR'' 2002b; 51: 823.</ref> organ transplant,<ref>CDC. "West Nile virus infection in organ donor and transplant recipients - Georgia and Florida, 2002." ''MMWR'' 2002e; 51: 790.</ref> intrauterine exposure,<ref>CDC. "Intrauterine West Nile virus infection - New York, 2002." ''MMWR'' 2002a; 51: 1135-1136.</ref> and breast feeding.<ref>CDC. "Possible West Nile virus transmission to an infant through breast-feeding - Michigan, 2002." ''MMWR'' 2002d; 51: 877-878.</ref> Since 2003 blood banks in the US routinely screen for the virus amongst their donors.<ref>CDC. "Detection of West Nile virus in blood donations - United States, 2003." ''MMWR'' 2003; 52: 769-772</ref> As a precautionary measure, the UK's [[National Blood Service]] runs a test for this disease in donors who donate within 28 days of a visit to the United States or [[Canada]].


==References==
==References==

Revision as of 05:00, 11 September 2014


Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Overview

West Nile virus pathophysiology

Transmission

Birds are the main reservoir of West Nile virus (WNV), but transmission of the virus is by mosquito bite of an infected bird with high-level viremia, such as birds of the family Passeriformes.[1] Thus, transmission is frequently denoted as "bird-mosquito-bird" transmission. Although direct bird-to-bird transmission has been speculated, further validation is still required.[2] Other species may also be infected, such as horses, cats, and dogs. Humans are considered dead-end hosts because the disease rarely progresses to viremia in humans, making transmission of the virus from a human unlikely except in some reported cases of transmission by blood transfusion, breastfeeding, or organ transplantation.[3][4][5]


Mosquitoes responsible for viral transmission belong to different families, varying based on geographical location:[6]

  • Culex pipiens: Northern half and West of USA
  • Culex quinquefasciatus: Southeast and West of USA
  • Culex tarsal: West of USA

Pathogenesis

Following inoculation, replication of WNV takes place in Langerhans epidermal dendritic cells, which are antigen-presenting immune cells.(26) These cells then migrate to lymph nodes, resulting in lymph node drainage, followed by viremia and dissemination of the virus into other organs, namely the spleen and the kidneys. Within one week, the virus is successfully cleared from serum and tissue compartments among immunocompetent individuals.

References

  1. ↑ "Emerging Infectious Diseases".
  2. ↑ Komar N, Langevin S, Hinten S, Nemeth N, Edwards E, Hettler D; et al. (2003). "Experimental infection of North American birds with the New York 1999 strain of West Nile virus". Emerg Infect Dis. 9 (3): 311–22. doi:10.3201/eid0903.020628. PMC 2958552. PMID 12643825.
  3. ↑ Iwamoto M, Jernigan DB, Guasch A, Trepka MJ, Blackmore CG, Hellinger WC; et al. (2003). "Transmission of West Nile virus from an organ donor to four transplant recipients". N Engl J Med. 348 (22): 2196–203. doi:10.1056/NEJMoa022987. PMID 12773646.
  4. ↑ Pealer LN, Marfin AA, Petersen LR, Lanciotti RS, Page PL, Stramer SL; et al. (2003). "Transmission of West Nile virus through blood transfusion in the United States in 2002". N Engl J Med. 349 (13): 1236–45. doi:10.1056/NEJMoa030969. PMID 14500806.
  5. ↑ Centers for Disease Control and Prevention (CDC) (2002). "Possible West Nile virus transmission to an infant through breast-feeding--Michigan, 2002". MMWR Morb Mortal Wkly Rep. 51 (39): 877–8. PMID 12375687.
  6. ↑ Petersen LR, Brault AC, Nasci RS (2013). "West Nile virus: review of the literature". JAMA. 310 (3): 308–15. doi:10.1001/jama.2013.8042. PMID 23860989.


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