Mosquito-borne Diseases

1. Mosquitoes carry quite a few diseases of great importance to humans. We have all heard the names: Dengue Fever, Yellow Fever, Malaria, West Nile Virus. All of these diseases are carried to humans by mosquitoes. Fortunately in Washington State we are not impacted by Dengue, Yellow Fever or Malaria. It still remains to be seen how we will be impacted by West Nile Virus. For some background… Mosquitoes are insects belonging to the order Diptera, the True Flies. Like all True Flies, they have two wings, but unlike other flies, mosquito wings have scales. Female mosquitoes have mouthparts that form a long piercing-sucking proboscis. Males differ from females by having feathery antennae and mouthparts not suitable for piercing skin. A mosquito’s principal food is nectar or similar sugar sources. Females require a blood meal to have viable eggs. There are over 2500 different species of mosquitoes throughout the world: about 200 species occur in the United States. Mosquitoes carry quite a few diseases of great importance to humans. We have all heard the names: Dengue Fever, Yellow Fever, Malaria, West Nile Virus. All of these diseases are carried to humans by mosquitoes. Fortunately in Washington State we are not impacted by Dengue, Yellow Fever or Malaria. It still remains to be seen how we will be impacted by West Nile Virus. For some background… Mosquitoes are insects belonging to the order Diptera, the True Flies. Like all True Flies, they have two wings, but unlike other flies, mosquito wings have scales. Female mosquitoes have mouthparts that form a long piercing-sucking proboscis. Males differ from females by having feathery antennae and mouthparts not suitable for piercing skin. A mosquito’s principal food is nectar or similar sugar sources. Females require a blood meal to have viable eggs. There are over 2500 different species of mosquitoes throughout the world: about 200 species occur in the United States.

2. Mosquito-borne Diseases Western equine encephalitis and St. Louis encephalitis Both have occurred in Washington but no reported cases since early 1980’s West Nile virus Detected in 1999 in New York City Detected in Washington and 43 other states in 2003 Continued surveillance effort in Washington Insects along with Crustaceans and Arachnids are part of the Phylum Arthropoda. These are animals with segmented bodies and jointed appendages. Arthropod-borne viruses, i.e. arboviruses, are viruses that are maintained in nature through biological transmission between susceptible vertebrate hosts by blood feeding arthropods (such as mosquitoes or ticks. Vertebrate infection occurs when the infected arthropod takes a blood meal. There are four main virus agents of encephalitis in the U.S: eastern equine encephalitis (EEE), western equine encephalitis (WEE), St. Louis encephalitis (SLE) and La Crosse (LAC) encephalitis, all of which are transmitted by mosquitoes. Insects along with Crustaceans and Arachnids are part of the Phylum Arthropoda. These are animals with segmented bodies and jointed appendages. Arthropod-borne viruses, i.e. arboviruses, are viruses that are maintained in nature through biological transmission between susceptible vertebrate hosts by blood feeding arthropods (such as mosquitoes or ticks. Vertebrate infection occurs when the infected arthropod takes a blood meal. There are four main virus agents of encephalitis in the U.S: eastern equine encephalitis (EEE), western equine encephalitis (WEE), St. Louis encephalitis (SLE) and La Crosse (LAC) encephalitis, all of which are transmitted by mosquitoes.

3. Mosquito-borne Disease Surveillance Pre-1960’s No record of state activity 1960’s First statewide mosquito survey published in 1966 1960’s Mosquito Control Districts formed in Eastern Washington 1970’s Sentinel flocks used in Benton and Grant County

4. Mosquito-borne Disease Surveillance 1980’s Last confirmed human and horse cases of encephalitis 1990’s Zoonotic Disease program established in DOH 2001 DOH initiates WNV surveillance

5. Yakima Valley Encephalitis Outbreaks 1939 31 cases 1940 58 cases 13 fatal 1941 26 cases 3 fatal 1942 28 cases 2 fatal (Reported in August 1945 Journal of American Medical Association) These illnesses and deaths were the driving force for creation of many of the currently operating mosquito control districts in Washington. Fifteen mosquito control districts now operate in 13 counties. Ten of the districts are in eastern Washington. These illnesses and deaths were the driving force for creation of many of the currently operating mosquito control districts in Washington. Fifteen mosquito control districts now operate in 13 counties. Ten of the districts are in eastern Washington.

8. West Nile VirusIn the United States Since the outbreaks of the 1930’s and 1940’s, surveillance for mosquito-borne encephalitis has been sporadic. The last comprehensive survey of mosquito species statewide was conducted in the 1960’s. In 2000 DOH under a grant from the CDC began working to establish routine mosquito-borne disease surveillance with local heath jurisdictions, mosquito control districts , and other partners in 2000.Since the outbreaks of the 1930’s and 1940’s, surveillance for mosquito-borne encephalitis has been sporadic. The last comprehensive survey of mosquito species statewide was conducted in the 1960’s. In 2000 DOH under a grant from the CDC began working to establish routine mosquito-borne disease surveillance with local heath jurisdictions, mosquito control districts , and other partners in 2000.

9. WNV Background First isolated in the West Nile District of Uganda, 1937 Recognized as a cause of inflammation of the spinal cord and brain with outbreak in elderly patients, Israel, 1957 Equine disease noted in Egypt and France in the early 1960s 1999 “Old World” virus arrives in the “New World” The history of the WNV dates back to 1937 with gradually increasing knowledge about the virus and the way it manifests itself in humans and animals. It was first recognized as a flu-like illness, then, in 1957 as a cause of meningitis and encephalitisThe history of the WNV dates back to 1937 with gradually increasing knowledge about the virus and the way it manifests itself in humans and animals. It was first recognized as a flu-like illness, then, in 1957 as a cause of meningitis and encephalitis

10. West Nile Outbreaks Israel 1951-1954, 1957, 2000-2002 France 1962, 2000 South Africa 1974 Romania 1996-1997 Italy 1997 Czech Republic 1998 Republic of the Congo 1998 Russia 1999 United States 1999-2002 Israel and France have both had recurring outbreaks of WNV. A similar pattern could occur in the U.S. with periodic outbreaks over time.Israel and France have both had recurring outbreaks of WNV. A similar pattern could occur in the U.S. with periodic outbreaks over time.

11. Outbreak Timeline The same information as on the previous slide shown on a timeline. Causes of recent clustering is not known but some speculate that climate change or a decline in mosquito control programs worldwide may have had some effect.The same information as on the previous slide shown on a timeline. Causes of recent clustering is not known but some speculate that climate change or a decline in mosquito control programs worldwide may have had some effect.

12. West Nile Virus Transmission Cycle First lets review the theory behind sentinel bird surveillance programs. Birds are the main vertebrate amplification hosts in the WNV transmission cycle. Mammals such as horse and human beings are simply incidental hosts. Therefore, there should be many more birds infected than mammals, and infection should occur in birds prior to infection in mammals. Thus birds should make effective sentinels for WN virus activity. There is no known animal-to-human or animal-to-animal transmission. There has been some documentation of bird to bird transmission. Humans and horses don’t have enough virus in their systems to infect other mosquitoes. There has been transmission of the virus from blood transfusion, organ donation, from mother to unborn child and from breast milk to infant. First lets review the theory behind sentinel bird surveillance programs. Birds are the main vertebrate amplification hosts in the WNV transmission cycle. Mammals such as horse and human beings are simply incidental hosts. Therefore, there should be many more birds infected than mammals, and infection should occur in birds prior to infection in mammals. Thus birds should make effective sentinels for WN virus activity. There is no known animal-to-human or animal-to-animal transmission. There has been some documentation of bird to bird transmission. Humans and horses don’t have enough virus in their systems to infect other mosquitoes. There has been transmission of the virus from blood transfusion, organ donation, from mother to unborn child and from breast milk to infant.

13. Geographic Distribution: Map showing worldwide distribution of West Nile virus and other related viruses at the beginning of 2000 (before the 2000 mosquito season in the United States). West Nile virus has been described in Africa, Europe, the Middle East, west and central Asia, Oceania (subtype Kunjin), and most recently, North America. In the U.S. through 2002, WN virus has been documented in 44 states and the District of Columbia.Geographic Distribution: Map showing worldwide distribution of West Nile virus and other related viruses at the beginning of 2000 (before the 2000 mosquito season in the United States). West Nile virus has been described in Africa, Europe, the Middle East, west and central Asia, Oceania (subtype Kunjin), and most recently, North America. In the U.S. through 2002, WN virus has been documented in 44 states and the District of Columbia.

14. WNV in the US Speculated Pathways of Introduction Human-transported bird Legal Illegal Human-transported mosquitoes Storm-transported bird Intentional introduction (terrorist event)-not likely Infected human traveler-not likely WNV most likely introduced by bird(s). Infected mosquitoes could have arrived in a cargo shipment. Migrating birds have been blown off their migration route and an infected bird possibly could have mingled with North American birds. WNV is not an effective bioterrorism weapon—Low human susceptibility, requires mosquitoes, no human-to-human transmission. An infected human traveler is not likely because humans are a dead end host. WNV most likely introduced by bird(s). Infected mosquitoes could have arrived in a cargo shipment. Migrating birds have been blown off their migration route and an infected bird possibly could have mingled with North American birds. WNV is not an effective bioterrorism weapon—Low human susceptibility, requires mosquitoes, no human-to-human transmission. An infected human traveler is not likely because humans are a dead end host.

15. WNV Symptoms High Fever Headache and body aches Skin rash Swollen lymph glands Neck stiffness Disorientation Convulsions WNV is hard to acquire. Only a small number (less than 1%) of mosquitoes are infected with the virus. Most people who are infected with the West Nile virus will not have any type of illness. It is estimated that 20% of the people who become infected will develop West Nile fever: mild symptoms, including fever, headache, and body aches, occasionally with a skin rash on the trunk of the body and swollen lymph glands. The symptoms of severe infection (West Nile encephalitis or meningitis) include headache, high fever, neck stiffness, stupor, disorientation, coma, tremors, convulsions, muscle weakness, and paralysis. It is estimated that 1 in 150 persons infected with the West Nile virus will develop the more severe form of disease. WNV is hard to acquire. Only a small number (less than 1%) of mosquitoes are infected with the virus. Most people who are infected with the West Nile virus will not have any type of illness. It is estimated that 20% of the people who become infected will develop West Nile fever: mild symptoms, including fever, headache, and body aches, occasionally with a skin rash on the trunk of the body and swollen lymph glands. The symptoms of severe infection (West Nile encephalitis or meningitis) include headache, high fever, neck stiffness, stupor, disorientation, coma, tremors, convulsions, muscle weakness, and paralysis. It is estimated that 1 in 150 persons infected with the West Nile virus will develop the more severe form of disease.

16. Distribution of WNV Before 1999 WNV was not found in the U.S before 1999.WNV was not found in the U.S before 1999.

17. Distribution of WNV as of November 1999 Distribution maps show states where the virus was identified either in mosquitoes, birds, horses or humans.Distribution maps show states where the virus was identified either in mosquitoes, birds, horses or humans.

18. Distribution of WNV as of November 2000

19. Distribution of WNV as of November 2001

20. Distribution of WNV as of November 2002 WNV has also been spreading westward across Canada.WNV has also been spreading westward across Canada.

21. Distribution by County October 7, 2002 Lack of surveillance possibly the reason that not all counties are showing positive in states affected a year or more.Lack of surveillance possibly the reason that not all counties are showing positive in states affected a year or more.

22. Case Summary 1999-2002 2001 Horse cases totaled 733. Outcomes available for 470 with 156 deaths. Among the 66 cases that were reported in 2001, the median age was 68 years with a range of 19 to 90 years. Update at www.cdc.gov and www.aphis.usda.gov/oa/wnv/wnvstats.html2001 Horse cases totaled 733. Outcomes available for 470 with 156 deaths. Among the 66 cases that were reported in 2001, the median age was 68 years with a range of 19 to 90 years. Update at www.cdc.gov and www.aphis.usda.gov/oa/wnv/wnvstats.html

23. WNV Case-Patient Demographics & Mortality United States, 1999-2002* In 2001, there were 9 deaths attributed to the WNV infection a case fatality ratio of 14%. Note that fatality rates are based on identified cases. True fatality rate would be much lower. As you can see, there is no significant difference in the proportion of males or the case fatality rate between the 1999/2000 cases and the 2001 cases In 2001, there were 9 deaths attributed to the WNV infection a case fatality ratio of 14%. Note that fatality rates are based on identified cases. True fatality rate would be much lower. As you can see, there is no significant difference in the proportion of males or the case fatality rate between the 1999/2000 cases and the 2001 cases

24. Date of Symptom Onset, West Nile VirusUnited States, 1999-2001 Strong seasonality especially in northern states associated with mosquito populations and outdoor recreationStrong seasonality especially in northern states associated with mosquito populations and outdoor recreation

25. Protecting Public Health Surveillance Personal Protection and Education Mosquito Control There are three basic components to safeguarding public health.There are three basic components to safeguarding public health.

26. WNV Surveillance Dead birds (especially crows, jays, ravens and magpies) Mosquitoes Captive sentinels (e.g. chickens) Veterinary surveillance Human surveillance WNV surveillance can involve five different activities. Certain birds are more susceptible to the virus and are therefore better indicators of its presence. Mosquito surveillance can provide information on where vector species of mosquitoes are located so that control efforts provide maximum benefit. Sentinel chicken flocks can be placed in areas where vector species occur. A blood sample is collected from each chicken, usually every two weeks, and tested for WNV antibodies. Veterinarians should have horses showing symptoms of encephalitis tested for WNV. Physicians should test suspected cases of encephalitis for WNV. WNV surveillance can involve five different activities. Certain birds are more susceptible to the virus and are therefore better indicators of its presence. Mosquito surveillance can provide information on where vector species of mosquitoes are located so that control efforts provide maximum benefit. Sentinel chicken flocks can be placed in areas where vector species occur. A blood sample is collected from each chicken, usually every two weeks, and tested for WNV antibodies. Veterinarians should have horses showing symptoms of encephalitis tested for WNV. Physicians should test suspected cases of encephalitis for WNV.

27. WNV Mosquito Species in Washington Aedes cinereus Aedes vexans Culex pipiens Culex restuans Culex tarsalis Anopheles punctipennis Coquilletidia perturbans Ochlerotatus canadensis Ochlerotatus japonicus Counties (39) 22 27 28 1 35 26 10 5 1 These Washington mosquitoes have tested positive for WNV in other parts of the U.S. There are about 50 species of mosquitoes in Washington and these have been associated with WNV so far. . They occupy a variety of habitats from containers to floodwater areas to storm water facilities. All counties have at least one potential vector species. In Island County we have Aedes cinereus, (ankle biter, most frequently found in woodland and open meadow pools and cattail swamps, doesn’t travel far) Culex pipiens (northern house mosquito, common in urban and suburban environments, likes artificial containers, clean or polluted water), Anopheles punctipennis (ponds and log pools, creeks and rivers, artificial containers – often associated with Culex pipiens, aggressive day and dusk biters, doesn’t travel far), Coquilletidia perturbans (marshes, ponds and lakes with thick aquatic vegetation. Larvae attach to vegetation stalks and do not need to rise to the surface to breathe, fierce evening biters) Culex restuans, (often found in foul water containing decaying grass or leaves, likes artificial containers). These Washington mosquitoes have tested positive for WNV in other parts of the U.S. There are about 50 species of mosquitoes in Washington and these have been associated with WNV so far. . They occupy a variety of habitats from containers to floodwater areas to storm water facilities. All counties have at least one potential vector species. In Island County we have Aedes cinereus, (ankle biter, most frequently found in woodland and open meadow pools and cattail swamps, doesn’t travel far) Culex pipiens (northern house mosquito, common in urban and suburban environments, likes artificial containers, clean or polluted water), Anopheles punctipennis (ponds and log pools, creeks and rivers, artificial containers – often associated with Culex pipiens, aggressive day and dusk biters, doesn’t travel far), Coquilletidia perturbans (marshes, ponds and lakes with thick aquatic vegetation. Larvae attach to vegetation stalks and do not need to rise to the surface to breathe, fierce evening biters) Culex restuans, (often found in foul water containing decaying grass or leaves, likes artificial containers).

28. Estimated Sensitivity of WNV Surveillance Methods In most areas, the virus is first detected in birds, followed by mosquitoes, horses, then humans.In most areas, the virus is first detected in birds, followed by mosquitoes, horses, then humans.

29. Personal Protection Wear long sleeves & pants in mosquito-infested areas Use repellant containing DEET (N,N-diethyl-3-methylbenzamide) and follow directions carefully Limit outdoor activities at dawn and early evening Repair holes in door & window screens These are the most effective measures a person can take to avoid WNV exposureThese are the most effective measures a person can take to avoid WNV exposure

30. Habitat Reduction Eliminate standing water (flower pots; tires; wheelbarrows; wading pools) Change the water in birdbaths at least weekly Aerate and chlorinate swimming pools and hot tubs; cover if possible Consider mosquito-eating fish for your pond Keep gutters clean to prevent standing water Spread the word: educate your friends and neighbors Reducing artificial habitat around homes and stable areas can further reduce exposure. Mosquito Problems Start at Home. Don’t’ give them a chance!Reducing artificial habitat around homes and stable areas can further reduce exposure. Mosquito Problems Start at Home. Don’t’ give them a chance!

31. The statewide response plan provides detailed recommendations for communities in dealing with WNV and other mosquito-borne diseases like St. Louis encephalitis and western equine encephalitis.The statewide response plan provides detailed recommendations for communities in dealing with WNV and other mosquito-borne diseases like St. Louis encephalitis and western equine encephalitis.

32. Want More? www.doh.wa.gov www.cdc.gov www.cfe.cornell.edu/erap/WNV/ Your local health department Additional information is available from these resources. ICHD also has the following resources on hand: Brochures, posters and bookmarks. WA State Mosquito Response Plan, Nov. 2002. Mosquitoes of Public Health Importance and their Control, U.S. Dept. of Health & Human Svcs. 1993. Centers for Disease Control and Prevention. Public Health Pest Control Manual, National Public Health Pesticide Applicator Training Manual. No. 2002. Also available at http://vector.ifas.ufl.edu DOH Zoonotic Disease Manual, Additional information is available from these resources. ICHD also has the following resources on hand: Brochures, posters and bookmarks. WA State Mosquito Response Plan, Nov. 2002. Mosquitoes of Public Health Importance and their Control, U.S. Dept. of Health & Human Svcs. 1993. Centers for Disease Control and Prevention. Public Health Pest Control Manual, National Public Health Pesticide Applicator Training Manual. No. 2002. Also available at http://vector.ifas.ufl.edu DOH Zoonotic Disease Manual,