Anthony Shaya - Zika Virus Implications for the 21st Century

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This event was graciously sponsored by the Jupiter Medical Center!

On Friday, September 9, 2016, Dr. Anthony Shaya, MD, MPH, FACOG, who is a current Member and former Chairman of the Department of Obstetrics and Gynecology at the Jupiter Medical Center, spoke about the current state of the art of Zika Virus with respect to knowledge, diagnosis, epidemiology, and treatment options.  The slides from his presentation can be found by clicking here, but a written summary of his presentation is outlined below.  Dr. Shaya credits much of this information to Dr. Alina Alonso, MD, Director of Palm Beach County, Florida Department of Health.

Epidemiology:

Zika virus was discovered in 1947 just before the discovery of other african mosquito-borne viruses like Chikungunya virus and Dengue fever virus.  Until recently, it had remained restricted to Africa, but has recently spread along tropical zones across the world, currently being found in South America, Africa, India, China, Australia, and south-east Asia.

It has taken root in Florida (29 cases from local mosquito bites as of August 24, 2016), and is expected to spread through the southeastern region, the Texas Gulf of Mexico region, and the southern two-thirds of the Atlantic Seaboard United States, especially during non-winter seasons.  California and Hawaii are buffered by desert climates and/or the Pacific Ocean, but alternative transmission of the virus or of the mosquito may result in the virus taking root there eventually as well.  The best large pool of data about epidemiology has been collected in Brazil.  However, data of infection and disease rate within the U.S. will provide more accurate transmission and disease rates for U.S. citizens.  This is primarily due to better health and environmental quality of the U.S.A. vs. Brazil.  Although a pandemic is possible for Zika virus, it is equally possible that the infection rate may run its course and stop spreading, much like what happened for Ebola virus in the 2014/2015 year.

Most cases of Zika infection in the USA are due to travel-associated cases (2487 as of August 24, 2016) in which people caught Zika virus from being bit by mosquitos (99%) or by sexual contact (1%) while travelling in tropical climates; only 7 of these cases (0.3%) developed into Guillain-Barré syndrome.

Mosquitos and anti-mosquito stretegies:

Zika virus is transmitted by two types of mosquitos, Aedas aegypti  (the primary agent) and Aedas albopictus.  Both species of mosquitos are tropically restricted on a year-to-year basis, but both species can migrate to temperate climates in warmer seasons or by tropical storms.

As with other mosquito-borne diseases, the most effective ways to protect oneself from viral infection (especially if living in or travelling to rural areas where aerial spraying may not occur) is to:

    • wear long-sleeved clothing
    • use insect repellant (DEET is most effective; oil of lemon eucalpytus and paramethanediol are also effective)
    • use mosquito netting or fine screening for outdoor activities, and
    • eliminate standing pools of stagnant water or water containing rotting material.
    • Limiting outside exposure in the evenings when mosquitos come out can also help reduce viral infection rates.

Because these mosquitos can carry multiple viruses (especially in urban areas where multiple people can be bit by individual mosquitos) , there is a significant chance of co-infection with Zika virus and another virus (like those described above), and symptoms may be due to multiple infections.

Direct Person-to-person infection:

In addition to mosquito-mediated transmission from person to person, there is evidence that the virus can be transmitted directly between people by way of in-the-body fluid exchange.  This exchange can occur during acts such as blood transfusion, sexual contact, through the placenta during pregnancy, and from maternal fluids to fetal skin during birth.  The virus can be detected in outside-the-body fluids like breast milk, saliva, urine, and maybe also sweat, but infection from these fluids has NOT yet been reported.  Because of the prolonged presence of the Zika virus in some people (see below), sexual contact after diagnosed Zika infection is obviously discouraged for at least 3 months, especially if a pregnancy with an infected individual is planned or is known during that period.

Symptoms and duration of infection:

Genetically and biochemically, the Zika virus resembles other flaviviruses (these include Dengue fever virus, West Nile Virus, yellow fever virus, and Japanese encephalitis virus).  Expectedly, disease caused by Zika virus resmbles diseases caused by other flaviviruses.  Importantly, 80% of the population will not show significant symptoms to the virus infection, or will feel symptoms indistinguishable from other viral infections, and may be poor carriers of the virus.  In the 20% who are susceptible (research is ongoing trying to determine who is at risk), viral symptoms show after an incubation period of 2-14 days and resemble those of a milder Dengue fever or Chikungunya fever:  (often) low-grade fever, red spotty rash, and joint pain are most commonly observed.  In some infected individuals, muscle pain, headache, vomiting, pain felt behind the eyes (called retro-orbital pain), and (distinctively) conjunctivitis may also also observed.  Conjunctivitis should co-present with retro-orbital pain -- the appearance of the virus in outside-of-body fluids coupled with the lack of active immunity in eye tissues may explain the co-presentation of retro-orbital pain and conjunctivitis.  Symptoms generally resolve within a week, with the infected individuals developing permanent immunity and permanent protection against subsequent re-infections.  The virus can persist in bodily fluids and extracorporeal secretions for months afterward in some individuals, but in most people does not cause disease. 

In some cases, cases of Guillain-Barré syndrome (muscle weakness due to lack of motor muscle activity resulting from peripheral nerve demyelination) and poor pregnancy outcomes (like microcephaly) have been reported.  When subjected to a critical evaluation, The incidence of microcephaly from Zika virus is hard to determine because the statistics are not consistent with one another:  microcephaly occurs at a 0.02-0.12% rate throughout the USA, at a 0.07% rate in Florida, a much higher rate in Brazil (13-29% of zika-infected mothers; 4-8% overall in Brazil), but only a 1% rate in French polynesia and Bolivia.  Other factors may explain the surge in microcephaly in Brazil, especially beause the microencephaly peak does not match the incidence peak for Zika infection.  Also many other well-established risk factors for microcephaly need to be accounted for, including:

    • genetic abnormalities
    • noninfectious complications of pregnancy
    • placental infection by other, far more common viruses like cytomegalovirus (CMV), herpes simplex, measles or rubella
    • placental infection by microbial agents like Toxoplasma species, syphillis, or gonorrhea
    • nutritional complications like phenylketonuria, generalized malnutrtion, hypothyroidism, or diabetes.  

Treatment and detection:

Although no vaccine is currently available, it is expected that a vaccine to Zika virus will be easily developed due to the ability for most people to effectively fight the virus, and the relative lack of immune-evading virulence factors in Zika infection.

One can be tested for Zika virus in the USA by testing one's blood for the presence of antibodies directed to Zika virus (usually IgM antibodies but IgG antibodies are also detected); however, it is very common for antibodies can remain for a period of time after the virus recognized by the antibodies is cleared.  A more extensive test can detect the presence of the virus in the blood (and/or saliva and/or urine) by detecting the viral RNA.  Testing is being done by the Florida Department of Health, and is being watched closely by the CDC.  The turnaround time for most governmentally-monitored diagnostic tests is usually about 1-2 weeks, but is currently taking up to 4 weeks for Zika virus results.  The CDC may request additional tests to test co-infection with other flavivirus.

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