Mosquitoborne Viral Diseases

Transcription

1 Mosquitoborne Viral Diseases Originally prepared by Tom J. Sidwa, D.V.M, M.P.H State Public Health Veterinarian Zoonosis Control Branch Manager Texas Department of State Health Services 1

2 AGENT Viruses MUST use a host s cells to reproduce 2

3 Arbovirus Mosquito Transmitted o arboviruses that cause human disease and are acquired in Texas West Nile Virus St. Louis encephalitis virus California encephalitis group o Other arboviruses that cause human disease, are acquired elsewhere, and may be diagnosed in Texas Eastern Equine Encephalitis Dengue (occasionally acquired in Texas) 3

4 VECTOR Amplifies the virus and transfers the virus to host 4

5 NOW Specifically West Nile Virus Southern house mosquito Exists between 36 o N (approximately the top of Texas) to 36 o S Nighttime-active o will feed on many animals and humans Also vector for St. Louis encephalitis virus Culex quinquefasciatus 5

6 RESERVOIR Source of virus for vector 6

7 Passerine birds (perching and songbirds) Family Corvidae ( stout billed birds) o Crows, jays o Most susceptible Acquiring the virus Dying from illness from the virus ( canary in the mine ) Virus in bloodstream for a short period Predominant species as a source of virus o Can vary by location, e.g. Houston area Mourning Doves Chicago suburbs American Robins Presumed lifetime immunity once infected 7

8 WNV Cycle Birds are source of virus for feeding mosquitoes Humans and horses are dead end hosts

9 DISEASE IN HUMANS 9

10 Classification Two classifications of West Nile virus illness: West Nile Fever (WNF) West Nile Neuroinvasive Disease (WNND) 10

11 WNF Signs and Symptoms Incubation period (period from bite to illness) o 2-15 days (average 3-6 days) Similar to many other viral illnesses 20-50% have a mild rash on arms, chest, and back Most have fever (but not all) Headache, fatigue, back pain, muscle aches, depressed appetite, nausea, vomiting, diarrhea, abdominal pain 11

12 WNND Signs and Symptoms May have any of the symptoms previously noted for West Nile Fever Much less likely to have rash Can present with encephalitis, meningitis, flaccid paralysis (generally one side of the body as in polio) or a mixture of these Eye involvement is common, especially chorioretinitis (inflammation of the lining of the retina) 12

13 <1% CNS disease WNV Human Reported cases Infection Iceberg ~20% West Nile Fever ~80% Asymptomatic Current theory: Once infected, always immune

14 Reported Cases WNV Human Infection Iceberg ~20% West Nile Fever ~80% Asymptomatic Only one in 150 cases of WNV results in WNND Meningitis (25-35%) Encephalitis or meningoencephalitis (60-75%) Myelitis or flaccid paralysis syndrome (rare) Current theory: Once infected, always immune

15 Behavioral Risk Factors for West Nile Disease in Texas Amount of time outside does not appears to be a risk factor. 41.7% reported less than 2 hours outside per day. Failure to use mosquito repellent is a major factor 70.7% of patients reported no repellent use

16 Risk Factors for WNND Age and pre-existing conditions are the most important risk factors for developing severe WNV infection o Age Over 50 2 fold greater risk Over 65 4 fold greater risk o Pre-existing Conditions, e.g. Diabetes Hypertension Immunosuppression o Nearly 5 fold greater risk o Solid organ transplant recipients may be at up to 40 times greater risk for developing severe WNV disease. 16

17 Diagnostic Approach Due to overlap with other illnesses, diagnosis is by laboratory testing Suspicion of WNV disease should be raised when o The signs and symptoms of the illness is suggestive o Summer to early fall o Evidence of virus circulation via surveillance data Reports of WNV disease in horses Reports of Human cases Reports of WNV positive mosquitos Reports of WNV positive blood donors 17

18 Course of West Nile Encephalitis Mandell Principles and Practice of Infectious Diseases

19 Diagnostic Lab Testing West Nile Illness PCR Caveat: There is short-term and low-level of virus in the blood, so the preferred blood test is for antibody detection in serum Should be ordered on Cerebrospinal Fluid (from spinal tap), as ~50% will be positive Serology Caveats: >95% of the time, test will identify antibody when present when serum specimens obtained between 7-10 days after illness onset False positive/cross-reactive blood IgM antibody can occur due to closely-related flaviviruses: o recent immunization with yellow fever or Japanese encephalitis vaccine, or o infection with related viruses such as Dengue, St Louis encephalitis IgM antibody to WNV can persist for 6 months or longer 19

20 Treatment No specific treatment No controlled studies to support any particular course of treatment Clinical course and outcomes are highly variable. 20

21 WNV: Long-Term Outcomes West Nile Fever: o Long term symptoms commonly reported o Study in Chicago % of 98 WNF o Average duration of symptoms 60 days 1 o Study in Colorado 2005 Two years after infection, quality of life measures were significantly reduced among 16 WNF patients 2 West Nile Encephalitis: o Long term disabling nervous system signs Tremors, movement disorders, subjective cognitive problems (e.g. forgetfulness and word-finding difficulties) in >50% More than 2 years after illness onset 21 1 Watson et al. Ann Intern Med, 141; Sejvar et al., J Neuropsychol 2: 2008

22 WNV: Long-Term Outcomes West Nile Fever: o Long term symptoms commonly reported o Study in Chicago % of 98 WNF o Average duration of symptoms 60 days 1 o Study in Colorado 2005 Two years after infection, quality of life measures were still significantly reduced among 16 WNF patients Watson et al. Ann Intern Med, 141; Sejvar et al., J Neuropsychol 2: 2008

23 WNV: Long-Term Outcomes West Nile Encephalitis: o Long term disabling nervous system signs Tremors, movement disorders, subjective cognitive problems (e.g. forgetfulness and word-finding difficulties) in >50% More than 2 years after illness onset Slow recovery 23

24 Vaccine No human vaccine o Any vaccine is years away from availability Horse vaccine o Licensed since 2003 o Effective and widely used 24

25 GEOGRAPHIC SPREAD 25

26 Origin Initial isolation West Nile District of Uganda in 1937 Epizootics (epidemic in animals) in horses with high death rate Until 1994, self-limiting infections of children with minimal if any symptoms Beginning in 1996, Eastern hemisphere outbreaks with human fatalities o Evolution of virus to produce more severe disease Before 1997, not considered a disease-causing condition in birds o Change occurred in Israel; this is thought to be the virus that entered the US Now persistently present in Europe, the Middle East, Africa, Asia, Australia, and United States 26

27 Virus Entry Into the USA Modification of CDC map at: activity/surv&control99maps.htm 27

28 Virus Movement through 2001 Modification of CDC map at: activity/surv&control01maps.htm 28

29 Rapid Spread of Virus Modification of CDC map at: activity/surv&control02maps.htm 29

30 West Nile Illness in Texas by Year Case Count Years WN Fever WNND Fatalities

31 Dallas Co cases Denton Co cases WEST NILE VIRUS Texas 1,879 human cases & 89 deaths Source: TX State Dept. of Health, 4/1/13

32 DSHS Role in Surveillance for Mosquitoborne Viruses 32

33 Zoonosis Control Branch Activities Disease surveillance for diseases that transmit from animals to people, including those that involve a vector. Streams of data for mosquitoborne viral diseases are: o Reports of WNV disease in horses o Reports of Human cases o Reports of WNV positive blood donors o Reports of WNV positive mosquitos Zoonotic disease investigations Support to local health departments o Serve as the local health department in counties that have none 33

34 Zoonosis Control Branch Activities All data streams are recorded and analyzed Reports are prepared and distributed to a wide range of stakeholders Agency Leadership, Preparedness staff, and a wide range of stakeholders are notified if an arbovirus o is starting seasonal circulation o occurs in an area that is not generally affected, or o causes disease in an unexpected manner (number or severity of cases) 34

35 DSHS Lab Services Mosquito Testing o Network of submitters send mosquitoes to DSHS Lab o Test for ALL mosquitoborne viruses using cell culture o Testing begins approximately May 1 and generally ends in November o A faster test can be used, especially during an outbreak Polymerase Chain Reaction (PCR) Human o Microsphere immunoassay (MIA) Detects antibodies to West Nile Virus protein Sensitive and cost effective IgM (Generally a sign of recent infection) IgG (Generally a sign of past infection unless IgM also present) 35

36 Mosquito Surveillance Zoonosis Control Branch receives testing data from DSHS Lab Other sources of mosquito testing o Local Government Labs o Texas A&M University o Private Labs PCR used Not all report results to ZCB 36

37 Mosquito Identification 37

38 Mosquito Pool 38

39 Mixer Mill 39

40 Sample Innoculation 40

41 Cell Observation 41

42 42

43 Contacts for Public Health Local Health Departments o Your first stop o Link to Local Health Department Department of State Health Services o Next stop when there is no local health department o Link to Regional Offices o Zoonosis Control Branch 43

44 QUESTIONS? 44