India should have a clear knowledge on Zika epidemiology before its next outbreak.
What is Zika?
Zika is a viral infection, spread by mosquitoes, the vector is the Aedes aegypti mosquito, which also spreads dengue and chikungunya.
Additionally, infected people can transmit Zika sexually.
Most people infected with the virus do not develop symptoms, the symptoms are similar to those of flu, including fever body ache, headache etc.
Additional symptoms can include the occasional rash like in dengue, while some patients also have conjunctivitis.
Also, fears around Zika primarily involve microcephaly, especially when pregnant women are infected.
Microcephaly is a condition in which babies are born with small and underdeveloped brains.
In India, Madhya Pradesh and Rajasthan saw large outbreaks of Zika in 2018.
How does dengue influence Zika outbreaks?
Two studies published earlier this year show conflicting evidence for the role of dengue in Zika outbreaks.
The first study showed that in mice, the presence of dengue antibodies led to more placental damage and restricted foetal growth due to Zika.
Another study showed that people infected by dengue were protected against Zika during an outbreak in Salvador, Brazil.
Given this conflicting evidence, scientists are very far from understanding what makes Zika deadly to foetuses.
This means that any data on how the pregnancies of Zika-infected women pan out in India can be of much help to the health authorities.
Thus, careful studies must be carried out to see if there is increased prevalence of microcephaly in India, and to understand the risk-factors.
What are the measures needed?
Screening - The TORCH (Toxoplasmosis, Other, Rubella, Cytomegalovirus, and Herpes) infections are known to cause foetal abnormalities, including microcephaly, among newborns.
Thus, wherever women are screened for TORCH, they must also be screened for Zika.
Monitoring - There is no evidence conclusively linking a particular viral strain or mutation with foetal anomalies so far.
The Indian Council of Medical Research (ICMR) said during the outbreak in Rajasthan, the Rajasthan strain did not have the S139N mutation – which is linked to microcephaly.
However, conclusion from several research across the globe shows that all Zika strains can cause microcephaly.
Thus, the health authorities in the states of Rajasthan and Madhya Pradesh must follow up on every pregnant woman who was diagnosed Zika positive last year.
Focus - Health authorities should gather information that concerns population immunity.
To study immunity, authorities must conduct seroprevalence surveys, in which they screen people in several States for antibodies to zika and subsequently identify pockets of low immunity in India.
Health authorities can then focus their efforts on these regions, because they would be most vulnerable to future outbreaks.
What should be done further?
Seroprevalence studies are not easy to do, given the cross-reactivity that plagues flaviviruses.
The Enzyme-linked immunosorbent Assay (ELISA), which is commonly used in seroprevalence studies to detect antibodies, can throw up false positives for Zika if a person has dengue antibodies.
This is because dengue antibodies can neutralise Zika and vice versa.
Hence, the researchers around the globe are working to develop alternative tests that are specific to Zika alone.
A multinational team has developed an ELISA test that is able to distinguish Zika from dengue.
The test was used in a survey at Managua, Nicaragua after a large epidemic hit the city in 2016.
It found that in 2017, 56% of tested adults had antibodies to Zika, suggesting that the city wouldn’t see another large epidemic in the near future.
Thus, India should consider doing such surveys in its own geographical region as soon as possible and should not wait until the mosquito season begins again.
