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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