The Zika threat

As if being the vector of the dengue virus is not bad enough, Aedes aegypti mosquitoes reinforce their image of being the tiniest mass killer and source of morbidity by being the vector of yet another virus which can cause fetal microcephaly and Guillain-Barré syndrome in babies of infected pregnant women.

A flavivirus, like dengue and chikungunya, the Zika virus is now labeled as a global concern as it has breached borders and is now reported in countries outside of Latin America. To date, 14 countries and territories in Central and South America and the Caribbean are now considered “hot spots” for Zika infection. Isolated cases have also been reported in the United States and Australia—all of whom were returning travelers from Latin American countries. No local transmission of the viral infection has been reported so far.

The clinical presentation may be quite deceiving, with relatively mild symptoms like fever, arthralgia, maculopapular rash, and conjunctivitis. The symptoms usually last only for a few days, rarely extending beyond a week. It can be easily dismissed as a mild touch of flu. In fact four out of five infected individuals are relatively asymptomatic. Hardly anyone with Zika infection needs hospital admission and there is no reported mortality from the infection. But the effect on the fetus of infected pregnant women can be devastating.

Why should we be concerned about the Zika virus?

Wherever the Aedes aegypti mosquitoes thrive, the Zika virus can thrive, too, and spread like bushfire. The whole country has now become a breeding ground for these mosquitoes, as evidenced by the year-round presence of dengue infections. We’re not so sure how confident our Department of Health (DOH) could be in really making sure we don’t have the virus here yet, as diagnosing the presence of the virus remains a challenge. Since 80 percent are usually asymptomatic and the symptomatic ones usually have relatively mild clinical presentations, it may be possible that we already have the Zika in our midst, but are just not able to detect the infected cases because of their asymptomatic or relatively mild clinical presentation.

The Center for Disease Control (CDC) in the United States recommend testing maternal serum from symptomatic women using reverse-transcription polymerase chain reaction (RT-PCR) within one week of symptom onset. Alternatively, antibody testing can be done within the first three days after symptom onset. After four or more days of infection, its sensitivity and specificity markedly decreases as there can be cross-reactivity to other flaviviruses especially dengue fever. The CDC also recommends amniotic fluid testing using RT-PCR, though its sensitivity and specificity are yet unknown.

The hitch is that these tests are not commercially available yet; and specimens need to be sent to the CDC for testing. Its feasibility should there be an outbreak can not be assured.

Our DOH should have a protocol requiring all hospitals—both government and private—to report all cases of microcephaly and Guillain Barre syndrome to detect any remarkable increase in occurrence compared to historical records.

Our best bet is to prevent the infection, and that is, by eradicating all possible breeding grounds for the Aedes aegypti mosquitoes. This way we can kill two birds with one stone—dengue and Zika.

Vital Signs Issue 84 Vol. 4, February 1-29 2016