By Dr. Geoffrey Modest
The Zika virus has made the headlines of late. Some details:
- Zika virus is a mosquito-born flavivirus, mostly transmitted by Aedes aegypti mosquitoes (which also seem proficient in transmitting dengue, chikungunya and yellow fever viruses)
- Zika infections have been documented through intrauterine as well as intrapartum transmission from a viremic mother. RNA from the virus is also detected in breast milk though transmission has not been documented by breastfeeding
- 80% of people are asymptomatic with the virus
- When symptomatic, there are usually only mild symptoms, with acute onset of fever, maculopapular rash, arthralgia, nonpurulent conjunctivitis. Lasting several days to 1 week. Fatalities are rare. But Guillan-Barre has been reported [note: there is a background incidence of Guillan-Barre. Not clear that the association with the Zika virus is causal, though a few cases have been found in Zika-infected individuals]
- In Brazil outbreak, Zika RNA has been identified in brain tissue, placenta and amniotic fluid
- Though there has been a dramatic increase in the numbers of infants with microcephaly or intracracial calcifications, it is unclear how many are associated with Zika
- Testing: there are PCR tests for the viral RNA, and both IgM ELISA and PRNT (plaque reduction neutralization test) testing for antibodies.There can be cross-reacting antibodies causing false positives, but the PRNT is more specific to Zika. Contact the State Dept of Public Health for info
- Since unclear which test is most reliable, CDC recommends both PCR and one of the antibody tests. All testing is done by the CDC or state labs.
- PCR testing should be within 2 days of birth. Also CSF, if obtained for other studies, and maternal serum
Zika virus has been found largely in Africa and Southeast Asia in the past. In May 2015, the WHO reported lots in the Western Hemisphere, including travelers to the US (though no active transmission found so far). But almost all of Central and South America has active cases, including Puerto Rico, Mexico, and pretty much everywhere else except Costa Rica, Argentina, Chile, Uruguay. Also active transmission reported in Cape Verde (see www.CDC.gov/travel for virus/travel updates)
See http://www.cdc.gov/mmwr/volumes/65/wr/mm6503e3er.htm for the CDC guidelines on evaluation and testing of infants with possible congenital Zika infection. In brief:
- Follow closely new mothers who were potentially exposed to Zika during pregnancy based on travel or residence in areas with Zika transmission
- Review fetal ultrasounds and maternal testing for Zika
- Test infants for the virus, if
- Infant with microcephaly or intracranial calcifications
- Infants born to mothers with positive or inconclusive test results for Zika virus
- Also, Zika virus is a nationally notifiable condition
- Infants with positive or inconclusive Zika tests: they should have ophthalmologic exam including retinal exam, within the first month of life, given reports of abnormal eye findings in those with possible congenital Zika. And repeat hearing screen at 6 months
- Still look for other possible etiologies of microcephaly or intracranial calcifications if these findings present, and treat appropriately (including consultation with dysmorphologist, a new term to me…., as well as routine testing for syphilis, toxo, rubella, cmv, lymphocytic choriomeningitis virus infection, hsv) [even with appropriate training and interest, I’m not sure I would like the word “dysmorphologist” to be attached to my name]
- In infants without any findings at birth but born to a Zika-positive mother, test the infant for Zika infection, and if possible infection, do routine exam with comprehensive neuro exam, check for hepatosplenomegaly and rashes, cranial ultrasound (unless normal in 3rd trimester check).
- Only mothers who report symptoms suggestive of Zika within 2 weeks in an area with ongoing Zika virus transmission should get Zika testing. Then if positive or inconclusive, test the infant.
- Management of Zika: nothing specific, no vaccines. Mothers should be encouraged to breastfeed, with apparent benefits outweighing potential risks
- Prevention: just avoid mosquitoes
The CDC recommends that “all pregnant women consider postponing travel to areas where Zika virus transmission is ongoing”, and if she goes there, avoid mosquitoes (remember that this mosquito, unlike the dawn/dusk types that transmit malaria, is more around in the daytime. So, use lots of anti-mosquito protection — though I’m not sure that is so great for the infant, the CDC recommends DEET, picaridin and IR3535 as more likely to be safe)
The NY Times reported on possible risk of Zika sexual transmission. See http://www.nytimes.com/2016/01/26/health/two-cases-suggest-zika-virus-could-be-spread-through-sex.html . Basically, there is a “theoretical risk” of sexual transmission per the CDC. A Tahitian man was exposed to the Zika virus in 2013, and a high level of virus was found in his semen and in his urine. Another was a malaria researcher in 2008, who was collecting mosquitoes for a malaria study in Senegal. He developed rash, fatigue, headaches, bloodshot eyes, and genital pain/likely hematospermia late in the illness. Tests for malaria, dengue and yellow fever were negative. After his return to the US, his wife who had remained in the US, developed several of these symptoms. Frozen serum from both the researcher and wife were subsequently positive for Zika virus, and no other family members were positive, suggesting sexual transmission.
So, the clear concern here is yet another emerging infectious disease with potential dire consequences to those infected, unclear if there will be new and threatening modes of transmission, and lack of current vaccine or treatment. But overshadowing much of this is the effects of climate change. It turns out that even small degrees of warming lead to major changes in the territory for mosquitoes. New cases of dengue, for example, have migrated north to the US (sporadic new cases reported in Hawaii and Florida), though the range of the vector mosquito has spread considerably into the southern US