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Mosquito-borne Viral Diseases of Concern in Texas
Texas Association of Physician Assistants
Austin, Texas
September 15, 2017
Tom J. Sidwa, DVM, MPH
State Public Health Veterinarian
Learning Objectives
• Participants should be able to• Describe at a high level, the cycle of
transmission for mosquito-borne viral diseases
• Describe the major features of infection with Zika, dengue, and West Nile viruses
• Take appropriate action to mitigate the risk of contracting a mosquito-borne viral disease
www.cdc.gov
ArbovirusesARthropod BOrne Viruses
Vectors• Mosquitoes
• Ticks
• Other arthropods
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Requirements for Infection
• Disease agent
• Competent vector
• Susceptible population
• Reservoir in some cases
www.cdc.gov
Flaviviruses
• Zika virus
• Dengue virus
• West Nile virus
• St. Louis Encephalitis virus
• Japanese Encephalitis virus
• Yellow Fever virus
www.cdc.gov
Zika, Dengue, and Chikungunya
• Maintained in human-mosquito-human cycles
• Aedes aegypti is primary vector, Ae. albopictus secondary
• Infections may be asymptomatic
• Human disease may be mild or severe
• No treatment or vaccine
• Interventions at personal and community levels are key to preventing disease
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Public Health Response
Objectives
• Identify risk areas
• Eliminate mosquito breeding sites
• Minimize transmission
• Public education
• Early diagnosis
• Integrated vector management
Interventions at personal and community levels are key.
Communication and coordination are essential:
• With the public and medical community
• Between Epidemiology, Environmental Health, and Public Information/Education programs within each agency/jurisdiction
• Among neighboring Health Departments and Vector Control agencies on either side of the border
• Between State Public Health authorities
Public Health Response
Zika
•Single-stranded RNA virus
•3 Lineages: 2 African and 1 Asian
•1947 – First isolated in Zika forest (Uganda)
Source: https://news.uns.purdue.edu/images/2016/rossmann-zika.jpg
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Zika Transmission
• Mosquito Bites: Zika virus transmitted to people via bite of an infected Aedes species mosquito (Ae. aegypti and Ae. albopictus)• Predominantly Ae. aegypti• Same mosquitoes spread dengue and chikungunya
• Actively infected individual –> mosquito –> next individual.
Zika Transmission
• Transmitted by mosquito but spread geographically by humans
• Sexually: Zika virus can be spread to sexual partners
• To Unborn Baby: Zika virus can be passed from a pregnant woman to her baby during pregnancy or at delivery
• Subgenus Stegomyia
• Both are invasive species that are firmly established
• Optimal activity periods for these species are usually 2 hours after sunrise and several
hours before sunset, but can be active (and taking blood meals) anytime during the
daylight hours
• Flight range is limited to approximately 150 meters from emergence
• Ae. aegypti females take blood meals from humans exclusively; Ae. albopictus has a
broader host range
• Cavity breeders (in evolutionary past); use artificial, water-holding containers for
oviposition
• Synathropophilic: close association with humans
• Ae. aegypti is the more efficient vector: multiple blood meals/gonotrophic cycle12
Asian tiger mosquito Aedes albopictusYellow fever mosquito Aedes aegypti
Photo from: http://fmel.ifas.ufl.edu/research/exotic.shtml
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Extrinsic and Intrinsic Incubation: Chikungunya Example
From: Coffey et al. (2014) Viruses, 6(11), 4628-4663; doi:10.3390/v6114628
~5 – 7 days**~2 to 12 days with a
median incubation
period of 3 days* for
symptoms to
appear; viremic for
first ~7 days after
onset of illness
* Rudolph et al. (2014) Review Article: Incubation Periods of Mosquito-Borne Viral Infections: A Systematic Review. Am J. Trop. Med.
Hyg 90(5): 882 – 891
** Dupont-Rouzeyrol et al. (2012) Chikungunya Virus and the Mosquito Vector Aedes aegypti in New Caledonia (South Pacific Region).
12(12): 1036 – 1041
** Vega-Rua et al. (2014) High Level of Vector Competence…, Journal of Virology. 88(11): 6294 – 6306
Zika Virus Infection and Disease
• Both infections and disease are reportable• Most Zika infections are asymptomatic
(estimated 80%)• Symptoms are usually mild
• Fever, pruritic rash, arthralgia, conjunctivitis; can last several days to a week
• Rarely causes death or requires medical care
• Once a person has been infected, he or she is likely to be protected from future infections
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Zika Virus Disease
• Microcephaly and other fetal abnormalities• When infection is passed to developing
fetus in the womb, Zika can interrupt brain development
• Guillain-Barré Syndrome (GBS)• Zika virus infection is among the triggers
for GBS• GBS develops in a small proportion of
infections, much as it is after a variety of other infections
Zika and Pregnancy
• Infection can occur in any trimester
• Among the causes of microcephaly
• Risks of infection difficult to define
• The timing of infection may have differing impact on the pregnancy
• Not all pregnant women who are infected with Zika have adverse birth outcomes
• Percent of infants born with microcephaly to a woman infected with Zika virus during the first trimester of pregnancy is estimated to be between 1% and 13%
https://www.cdc.gov/zika/reporting/2017-case-counts.html (accessed 9/1/17)
Zika Cases in U.S. as of August 30, 2017Travel–Associated 223; Sexual Transmission 2
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Cases in TexasAs of August 18, 2017
County Cases
Bexar 2
Brazoria 1
Brazos 1
Cameron 6
Collin 1
Dallas 2
Denton 1
Harris 5
Lubbock 1
Smith 2
Total 22
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Counties Reporting Confirmed Zika Cases(As of 8/11/17)
Message for Pregnant Women
• The primary concern is about pregnant women
• Receive appropriate prenatal care
• Follow CDC travel guidance
• Do not travel to areas with active Zika transmission
• Avoid mosquito bites
• Protect yourself from sexual transmission
• Be aware of guidance about risk and need for testing
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Message for Providers
• Stay on top of the information, CDC guidance
• Talk to patients about travel, risk, testing, and pre-conception considerations
• Quickly report suspect cases to the health department
• Stay educated about how to collect, store and transport specimens for testing. Guidance at www.TexasZika.org
• Talk to pregnant patients and their partners about travel plans and need to strictly follow precautions
Texas Outlook• Texas is expected to have seasonally-
recurrent risk of local transmission of Zika virus by mosquitoes
• As with dengue, local transmission would not likely be sustained
• Many areas of Texas support Ae. aegypti and have concentrated human population; conditions that may facilitate local transmission
• Some areas are considered at higher risk –the Lower Rio Grande Valley, Gulf Coast, and large urban areas along the I-35 corridor
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http://www.paho.org/hq/index.php?option=com_content&view=article&id=11599&Itemid=41691&lang=en
Distribution of confirmed Zika cases. Mexico, 2015 – 2017 (as of EW 30)
Source: Data provided by the Mexico Secretariat of Health and reproduced by PAHO/WHO
Distribution of suspected and confirmed Zika cases by EW and sub-region. Region of the Americas, 2015 – 2017 (as of EW 32)
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http://www.paho.org/hq/index.php?option=com_content&view=article&id=11599&Itemid=41691&lang=en
Dengue Virus
• Flavivirus
• Vector is Aedes spp. mosquito
• Caused by any of 4 viruses
• DEN 1-4
• Three case classifications
• Dengue-like Illness
• Dengue
• Severe Dengue
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Dengue in the US
• US - Dengue is #1 cause of acute febrile illness in travelers returning from South-central and Southeast Asia, South America, Mexico and the Caribbean1
• Texas – Predominantly travel to Mexico
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1. Freeman et al., NEJM 2006.2. Data courtesy of Jennifer Lehman, CDC ArboNetcoordinator
Dengue in Texas
0
10
20
30
40
50
60
70
80
90
100
Imported Locally acquired Unknown
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Dengue in Texas
• 2013: 95 cases reported; 37 cases in Cameron County, 13 in Hidalgo County, and 1 in Willacy County; 23 locally acquired and 7 unknown
• 2008: 22 cases reported; one locally acquired in Hidalgo County
• 2005: 32 cases reported; outbreak in Matamoros affecting one Hidalgo County and 25 Cameron County residents; 5 locally acquired
• 1999: 66 cases reported; 55 cases in South Texas (28 in Webb County; others from Cameron, Hidalgo, Starr, Willacy and Nueces Counties; 16 acquired in South Texas)
• 1995: 29 cases reported; 13 in Cameron and Hidalgo Counties, including 7 locally acquired
Dengue in Texas, 2013
* 2016 data provisional
DSHS Arbovirus Activity in Texas: 2013 Surveillance Report www.dshs.texas.gov/idcu/disease/arboviral/westnile/summaries/
Outcome of Infection
• Of those infected
• 75% - no symptoms
• 25% - symptoms
• 95%-99% develop Dengue-like Illness or Dengue
• 1% -5% develop Severe Dengue
• 0.5 – 5% die
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Clinical Course
• Incubation 3-14 days
• Virus in blood – 2 days before and 7 days after illness onset
• Fever Phase - 2-7 days
• Critical Phase (CP) – 1-2 day period after the fever breaks
• Convalescent Phase – lasts 3-5 days after CP
• Recover or die
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Fever Phase
• Sudden fever onset
• Reddened face, neck, and chest for 1-2 days
• Headache, pain around eyes, muscle and joint pain, hemorrhage
• Rash on trunk spreading to face, arms, and legs 2-6 days after illness onset
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Critical Phase
• When fever breaks and lasts 1-2 days
• Most patients improve
• Small percent develop plasma leakage
• Concentration of blood
• Low blood protein
• Free fluid in chest and abdomen
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Critical Phase
• Small hemorrhages may appear on arms and legs and mucous membranes
• Severe abdominal pain
• Persistent vomiting
• Liver enlargement
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Convalescent Phase
• Takes 3-5 days
• Reabsorption of fluid in chest and abdomen over 2-3 days
• General wellbeing improves
• Laboratory results return to normal
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West Nile Virus
• Genus Flavivirus• Single stranded RNA virus• Genetic changes since entering USA have not seemed to alter its infectivity and severity
• 1937 - isolated in West Nile District of Uganda
• Mosquito vectors vary across the country• Texas
• Culex quinquefasciatus (primary)• Culex tarsalis (important vector in western Texas)
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41https://www.cdc.gov/westnile/statsmaps/preliminarymapsdata/incidencestatedate.html
West Nile Virus Neuroinvasive Disease Incidence2016 (as of January 17, 2017)
0
500
1000
1500
2000
2500
WN Fever WNND Fatalities
West Nile Illness in Texas by Year
Case C
ount
Years
Texas Department of State Health Services Data
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~80%Asymptomatic
~20%“West Nile Fever”
<1%WNNDdisease
WNV Human Infection “Iceberg”
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WNV Human Infection “Iceberg”
~80%Asymptomatic
~20%
“West Nile Fever”
<1%WNNDdisease
WNV Human Infection “Iceberg”
West Nile Fever
10-30% of infections
Fever, headache, rash, fatigue
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WNV Human Infection “Iceberg”
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~80%Asymptomatic
~20%“West Nile Fever”
<1%WNNDdisease
WNV Human Infection “Iceberg”
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WNV Human Infection “Iceberg”
Signs and SymptomsWest Nile Fever
• The period between mosquito bite and illness onset is 2-14 days (average 2-6 days)
• Presents like many other viral illnesses: acute, nonspecific influenza-like illness lasting 3-6 days
• High fever and chills, lack of energy, backache, headache, joint pain, muscle aches, and pain behind the eyes
• ~50% have mild rash on chest, back and arms (more frequent in children)
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Signs and SymptomsWest Nile Neuroinvasive Disease
• May show fever for 1-7 days• May be rise and fall a couple of times before development of neurologic
symptoms
• 15-20% have features suggestive of WN fever, including eye pain, facial congestion or a rash
• Of hospitalized patients, 2/3 with encephalitis (with or without associated meningitis), 1/3 with meningitis
• Flaccid paralysis can occur (resembling poliomyelitis): one-sided limb weakness or paralysis in absence of loss of sensation
• Can have other neurologic features, e.g. lack of balance
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Risk Factors
• Age is by far the most important risk factor for developing neuroinvasive WNV infection
• Residents of endemic areas and visitors are at higher risk
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• Outdoor occupations and outdoor recreational activities confer risk.
• Solid organ transplant recipients may be at up to 40 times greater risk for developing severe WNV disease.
Age and Relative Risk
• 1 in 5 infected develop WNF
• 1 in 150 infected develop WNND
• Patients over 50 years have a 10-fold increased of risk of neurologic symptoms
• Patients over 80 years have a 43-fold increased risk of neurologic symptoms
• Patients developing meningitis or severe encephalitis have a case fatality rate of 5-10%
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Prevention
• Prevent mosquito bites
• 4 D’s
• Avoid Dusk and Dawn
• Dress Appropriately
• Drain standing water
• Defend!!
• Follow the application instructions for repellents!
• Avoid travel to countries with Zikatransmission
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Thank you