by: Hillary Jarnagin, MD
I killed three mosquitoes in my house this week. Three! Apparently, no one has informed the mosquito population of North Texas that Christmas is in a couple of weeks and they should be dead and gone by now. With a warm fall and no hard freeze so far this winter, it’s no wonder these mosquitoes have outstayed their welcome. With my recent, unseasonably late, encounter with my tiny uninvited house guests and the first documented case of Zika virus contracted from a mosquito in south Texas at the end of November, I thought it would be appropriate to revisit what we know about the Zika virus and how to limit exposures and risks.4
As someone who was pregnant last year and caring for pregnant women, there was no escaping the concerns about the threat of the Zika virus and the potential implications of an acute infection during pregnancy on the development of the baby. In the year following the outbreak of the Zika virus in Brazil, obstetricians and pediatricians observed a larger than expected frequency of infants with small heads, redundant scalp tissue, defects in development in some areas of the brain, and varying degrees of associated neurocognitive impairment.1 Reports from Brazil in 2015-2016 suggested a link between Zika virus infection during pregnancy and a variety adverse pregnancy outcomes including spontaneous pregnancy loss, stillbirth, and birth defects affecting the brain, the nervous system, and the eye. Fortunately, the impact of the Zika virus in pregnancy has been relatively limited in the continental United States so far and the majority of cases involved patients who traveled to an area with an ongoing Zika outbreak or had unprotected sexual contact with a partner who did (99%). However, with the ease of travel, the longevity of the Zika virus in seminal fluid, and recorded cases of mosquito borne Zika virus in both Florida and now Texas, we should expect this to be an ongoing public health concern in the U.S. and abroad. According to the CDC, there have been about 3,500 cases of Zika virus in the United States and its territories (including Puerto Rico, American Samoa, and the U.S. Virgin Islands).1 Approximately 1,000 of these cases have been in pregnant women.1 Of these cases in pregnant women, the majority have been contracted through sexual transmission from an infected partner.
Let’s review what we know about this virus that was virtually unheard of in the Western hemisphere until about a year and a half ago. The Zika virus was discovered in a monkey in Uganda in the late 1940s.2 This virus belongs to the same family of viruses as Dengue, Chikungunya, Yellow Fever and West Nile2. All of these viruses can be transmitted to humans from the bite of an infected Aedes mosquito.2 Only 20% of patients will get symptoms.2 When they do occur, symptoms are usually mild and include low grade fever, rash, redness in the whites of the eyes, muscles aches, joint pain, and headache.3 Symptoms begin anywhere between three days and two weeks after the exposure.2 The acute infection will resolve spontaneously without treatment in about two to seven days.2 The first human case was documented in the early 1950s. Until the early 2000s, the Zika virus had not been seen outside of Africa and Asia. Prior to the Brazilian Zika Virus outbreak that began in 2015, there were two smaller outbreaks in the Yap Islands in Micronesia and in French Polynesia.2 It was not until this larger, more recent outbreak that the association of the Zika virus infection during pregnancy and the increased incidence of pregnancy loss, stillbirth, microcephaly and other birth defects was made. We have also learned from this larger scale outbreak that this virus can be sexually transmitted and that the virus remains in semen much longer than it does in the urine or blood and at significantly higher concentrations. While a Zika virus infection is usually of little consequence to a non-pregnant adult, the outbreak in Brazil has also highlighted an increased incidence of a rare autoimmune condition called Guillan-Barre syndrome.3 This disorder causes disruption of nerve signals in the peripheral nervous system resulting in muscle weakness and paralysis that begins in the limbs and, if it worsens, can affect the function of the muscles that control breathing.
So, what can be done to treat, prevent, or reduce the risk of getting this virus in the first place since an infection could have serious complications in reproductive aged women and their children? Efforts are underway to develop a vaccine for the Zika virus, but even if a potential vaccine was expedited through safety testing, we are likely still a couple of years away from having anything come to market for use. There is no treatment for the Zika virus and in the majority of adult patients, treatment would not be necessary. Zika virus can be passed to a human from the bite of an infected mosquito, from an infected pregnant woman to her unborn child through the placenta, or through sexual contact with an infected partner. Our main line of defense against infection is preventing exposure.
Additional efforts to reduce the mosquito population occur at the state and local level by spraying insecticide during the summer. Nationally, the Food and Drug Administration has recommended temporarily not accepting blood from donors who have recently traveled to or live in areas of active Zika virus transmission and for testing blood for the presence of the Zika virus.1 The use of genetically engineered Aedes mosquitos that will reduce the mosquito population by creating sterile offspring when breeding with native mosquitos is also under investigation.
Our knowledge and experience with the Zika virus is ever expanding and will continue to accumulate as the number of affected patients grows. I anticipate this outbreak will continue to be an international and domestic health concern in the years to come. As we learn more as physicians and scientists, recommendations will continue to evolve. We are still a little ways off from having effective strategies to completely prevent transmission of the virus either through vaccination programs or targeting the replication of the Aedes mosquito. As your provider, we will equip you with the most up to date information as it becomes available about protecting yourself and your family, and how to detect infection and monitor pregnancies with risks of Zika virus exposure and infection.