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Vector-Borne Vector-Borne Diseases of Public Diseases of Public Health Importance Health Importance Dawn M. Wesson Dawn M. Wesson Tulane University Tulane University New Orleans, Louisiana New Orleans, Louisiana

Vector-Borne Diseases of Public Health Importance Dawn M. Wesson Tulane University New Orleans, Louisiana.

Dec 14, 2015



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Vector-Borne Diseases of Public Health Importance Dawn M. Wesson Tulane University New Orleans, Louisiana Slide 2 Definition of Vector-Borne: A biological association between an arthropod (insect or arachnid) and a pathogen acquired by feeding on the blood of an infected vertebrate host Pathogen acquisition by the arthropod may also be through transovarial or venereal transmission Slide 3 Overview Mosquito transmitted pathogens Viruses Malaria Flea transmitted pathogens Plague Other rare insect transmitted pathogens present in the United States Slide 4 Mosquito Transmitted Pathogens Arboviruses (ARthropod-BOrne VIRUSES) West Nile virus (WNV) St. Louis encephalitis virus (SLE) California group viruses (CE & LACV) Western equine encephalitis virus (WEE) Eastern equine encephalitis virus (EEE) Dengue virus (DEN) Slide 5 Generalities About Arboviruses Seasonal most cases occur in warm months Incidence varies with time and place because ecological factors are important For each of these viruses, the ratio of clinical to subclinical infection varies (number of detected cases versus number actually infected) With the exception of dengue virus, humans are not important for virus survival Slide 6 Slide 7 West Nile Virus (WNV) The most common mosquito transmitted arbovirus causing human disease in the US Discovered in New York City in 1999 and has since spread to every state in the continental US and most other countries south of Canada Basic cycle: bird to mosquito (but recent work suggests eastern chipmunks could also be involved) Bird deaths (>300 spp.) associated with infection Slide 8 West Nile Virus Most human infection occurs by mosquito bite, July Oct. (longer season further south) Blood transfusion, infected tissue donation, placental, and accidental laboratory infections have also been documented 80% of all human infections show no symptoms of the symptomatic 20%, most go on to develop West Nile fever Slide 9 West Nile Virus After bite of infected mosquito, it takes 2-14 days for symptoms to occur Characteristics of WN Fever - fever, headache, fatigue and sometimes rash, swollen lymph glands and/or eye pain Severe disease occurs in up to 1% of infected individuals - meningitis and/or encephalitis and/or sometimes paralysis Approximately 10% severe cases die Slide 10 4269 cases (incl. severe and mild) 177 deaths 2006 WNV in the United States Slide 11 1999 WNV Incidence in the US 2000 WNV Incidence in the US 2001 WNV Incidence in the US 2002 WNV Incidence in the US 2003 WNV Incidence in the US 2004 WNV Incidence in the US 2005 WNV Incidence in the US 2006 WNV Incidence in the US Slide 12 Summary of WNV Severe Disease Cases and Deaths Slide 13 Primary WNV Vectors Northeastern and northcentral US Culex p. pipiens Southeastern US Culex p. quinquefasciatus and Cx. nigripalpus Southcentral US - Culex p. quinquefasciatus and Cx. salinarius Mountain west and western US Culex tarsalis and Cx. p. quinquefasciatus Slide 14 Locally Important or Secondary WNV Vectors Aedes vexans Aedes albopictus and Ae. aegypti Aedes triseriatus Aedes japonicus (newly introduced) Species of Coquillettidia, Culiseta, and Psorophora Other Culex and Aedes spp. Slide 15 West Nile Virus Severe Disease Risk Factors Exposure to infected mosquitoes when > 50 years of age (most fatalities > 75 years) Culex spp. mosquitoes - but over 60 mosquito spp. have been found naturally infected Recreational and/or occupational exposure in urban or rural setting Primary and secondary vectors can vary locally and regionally, so understanding local transmission is crucial! Slide 16 St. Louis Encephalitis Virus Distribution similar to WNV in New World only Bird mosquito cycle; similar primary mosquito vectors (Culex spp.) and transmission season to WNV But no extensive secondary vectors like WNV drought associated epidemic transmission Most similar to WNV in urban situations sparrows and other peridomestic birds important for amplifying virus Slide 17 Slide 18 SLE Symptoms and Risks 0 3,000 cases/year (1975), but usually smaller outbreaks; average of ~ 130 cases/yr Most infections asymptomatic or mild, with 3- 30% case fatality ratio Severe disease meningitis, encephalitis, coma, death Similar risk to WNV increasing age, outdoor exposure in urban or periurban areas Slide 19 La Crosse (California Group) Encephalitis Distribution in Eastern US and Canada Aedes triseriatus mosquito and chipmunk/ squirrel transmission cycle Vectors are woodland/suburban container inhabiting species Likely secondary or locally important vectors are Ae. albopictus and Ae. japonicus Slide 20 Slide 21 LACV Symptoms and Risk Approximately 70 cases/year Most infections asymptomatic or mild, with

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