Global Public Health Entomology Mosquitoes and the diseases they transmit: Yellow Fever 1"Asymptomatic Cases Inapparant/apparent ratio: 1/2 in naïve children prior exposure to some other flaviviruses can provide some immunity -> 22/1 ratio Mild fever cases Fever Nausea Headache Nose bleeding Slow heart rate Yellow fever symptoms 3-6 days Intrinsic Incubation Period 2"20%-50% death Yellow fever symptoms More Serious Cases (15% of those infected): Toxic phase High Fever Seizures Headache Nausea Dizziness Vomiting Red eyes Bloody nose/gums Liver damage Jaundice Internal bleeding => Black Vomit 3"Yellow fever cycle Africa Transmission cycle of yellow fever in Africa Insert graph 3.11 Yellow fever is maintained in zoonotic (primates) jungle cycle (primates do not die) People entering the jungle can bring yellow fever into rural and/or urban cycle Rural cycle takes place at the edge of forests and various other mosquitoes are involved. Transmission between humans by Aedes aegyti in urban (villages and towns) cycle 4"Yellow fever cycle South America Transmission cycle of yellow fever in South America Yellow fever is maintained in zoonotic (primates) jungle cycle (primates die) People entering the jungle can bring yellow fever into urban cycle (villages and cities) No intermediate cycle Transmission between humans by Aedes aegypti in urban cycle Insert graph 3.12 5"Yellow Fever Control Vaccine available since 1937 (Max Theiler received Nobel Prize in 1951) Early vaccination programs were very successful -> few cases between 1940 and 1965 Currently about 50% of sub-Saharan countries routinely vaccinate against yellow fever (WHO recommends routine vaccination in all endemic countries Vaccine is in short supply (needs to be grown in eggs) Can"yellow"fever"be"eradicated?"But: Yellow fever is maintained in zoonotic cycle in primates Vaccine is available 6"1] Yellow fever is not caused by bacteria 2] Yellow fever is transmitted by Aedes aegypti 3] Yellow fever is not transmitted by air or “fomites” 4] Extrinsic incubation period of around 12 days is required to transmit virus by mosquitoes ! 5] Eradication of mosquitoes should prevent yellow fever Yellow fever Important conclusions from the Walter Reed commission 7"Yellow"Fever"in"the"US"Aedes%aegyp*%was"mostly"replaced"by"Aedes%albopictus"in"the"last""15"years"Occurs"occasionally"in"US"travelers"low"probability"of"reintroducDon"Current"Risk:"Why"did"it"disappear?"Urban"improvement"(piped"water"supply)"BeLer"quaranDnes"Window"screens"Vector"control""Different"ship"design"Yellow"fever"control"in"Havana"and"other"caribbean"areas""Possible"factors:"8"Public Health Entomology Lecture 12 West Nile and other Encephalitic Arboviruses Mosquitoes and the diseases they carry: 9"Animals Humans Epizootic Epidemic Enzoonotic Endemic Some terminology Zoonosis: infectious disease that can be transmitted from other animals to humans Reservoir host: host in which an infectious disease is maintained -> (often) no ill effect on the animal host -> enzoonotic Amplifying host: a host in which infectious agents multiply to high concentrations -> animal hosts get ill -> epizootic 10"Arboviruses Arthropod-Borne Viruses 501 animal viruses known or suspected to be transmitted by arthropods 134 have been documented to cause illness in humans With the exception of Dengue and Yellow Fever, -> humans are almost always the dead-end hosts Humans do not produce high enough viremia level for infection of vector. Most Arboviruses are zoonoses 11"Important Arboviruses causing human disease 12"Major epidemics of Arboviruses in the 1990’s 13"Increase in Arboviruses in last 20 years Reasons are complex and not fully understood -> mostly demographic and societal changes population growth urbanization deforestation -> complacency in vector control -> globalization increase in human migration trade in exotic animals (e.g. West Nile Virus) 14"Major Arboviruses in the US West Nile Virus Western Equine Encephalitis Eastern Equine Encephalitis St Louis Encephalitis Lacrosse Encephalitis Japanese Encephalitis: major arbovirus in S.E. Asia (does not occur in US) 15"West Nile Virus History First identified in 1937 in female from West Nile District in Uganda In this region WNV is just another childhood disease: Everyone is infected early in life. Muscle aches, fever, chills, -> lifelong immunity after first infection First detected outside home range in Israel in 1950’s 16"West Nile Virus History 1950’s Epidemics in Israel Virus was shown to be widespread in Eurasia Virus was considered of minor importance 17"West Nile Virus History 1990’s West Nile Epidemics appear more frequently Epizootics: Horses: Morocco 1996, Italy 1998, Israel 1998, France 2000 Birds: Israel 1997, 1998, 1999, 2000 Human epidemics: Algeria 1994, Tunisia 1997, Romania 1996, 1997 Czech Republic 1997, Congo 1998, Russia 1998, 1999, 2000; Israel 1999, 2000 Not reported to health authorities 18"West Nile Virus History Why did WNV epidemics appear? Most likely a new more virulent strain appeared with greater epidemic potential and spread through the Mediterranean and other geographic regions in the late 1990’s. 1999 WNV arrives in NY city 19"20"West Nile Virus 20% will develop West Nile Fever fever, headache, tiredness, body aches (can last several weeks) Severe disease: West Nile Encephalitis West Nile Meningitis, West Nile Meningoencephalitis headache coma high fever tremors stupor convulsions disorientation paralysis Death People > 50 are at highest risk Symptoms: 80% asymptomatic (1/150) Flavivirus Fatality rate 10% 21"22"2013: 1,204 Neuroinvasive cases, 114 deaths 23"West Nile virus (WNV) activity reported to ArboNET, by state, United States, 2012 (as of October 2, 2012) 2012: 3,969 neuroinvasive cases, 163 deaths Why so many cases in 2012 ? - Warm winter - Early spring - Wet summer 2014: 732 neuroinvasive cases, 47 deaths 24"West Nile Seasonality tive surveillance event, the median lead timewas38.5days(range:2–252days).In320(85%)of these counties, the lead time exceeded 14days(theapproximateup