The World Health Organisation (WHO) on Saturday, May 27, confirmed India’s first cases of the Zika virus. The health ministry reported that of the three cases, all from Bapunagar area of Ahmedabad in Gujarat, one was that of a pregnant woman. The virus, just like two other mosquito-borne infections — dengue and chikungunya — is caused by the same vector, the Aedes mosquito. With dengue and chikungunya widespread and endemic in most major cities, the country faces a challenge in tackling Zika, for which there is no effective vaccine.
What concerns on Zika do these three cases raise in India?
Zika is an “emerging viral disease” transmitted through the bite of infected Aedes mosquitoes, which also transmits dengue and chikungunya. Zika’s causative organism — Zika virus (ZIKV) — was first isolated in 1947 but until a few years ago, the infection was thought to lead to a relatively mild disease. The explosive outbreak of ZIKV in South America in recent years, however, has led to widespread concern, with reports of neurological complications ranging from Guillain Barre syndrome to microcephaly.
In 2013, French Polynesia reported an Zika outbreak and showed an increase in cases of Guillain Barre syndrome — a form of temporary paralysis in adults, that has links to other neurological complications. Two years later, in 2015, Brazil reported a significant increase in the incidence of microcephaly — a condition defined by unusually small heads and brain damage in infants, along with other defects like blindness, deafness, seizures and other congenital defects.
The microcephaly cases were reported in the northeastern parts of the country, coincident with a large increase in Zika cases. After these two incidents, the World Health Organisation declared the Zika virus as a health emergency in February 2016.
What are the challenges India faces in case of an outbreak?
The ZIKV and the four dengue virus serotypes (DENV-1 through to DENV-4) are mosquito-borne viruses belonging to the family Flaviviridae. The clinical representation of Zika virus is also similar to that of dengue. The number of dengue cases doubled from 2014 to 2015 and in 2016, the country was gripped by the chikungunya virus. Much like Zika, dengue and chikungunya infections, which co-circulate in most of the Zika endemic areas, are also responsible for maternofoetal (passed from mother to foetus) infections.
The primary challenge for the country therefore is to ensure that the three infections are rightly diagnosed as the trio show similar symptoms. Further, even if Zika has already been detected, it is recommended that patients are tested for chikungunya and dengue too.
What is the treatment protocol?
There is no drug or effective vaccine against the Zika virus. Patients are generally advised to rest and drink a lot of water. Treatment, if required, is mainly supportive, including through intravenous fluids and antipyretics. Anti-inflammatory drugs such as Ibugesic need to be avoided till dengue is completely ruled out. Testing for Zika virus should be done on pregnant women who have travelled to Zika endemic regions and those who show symptoms. The Indian Council for Medical Research (ICMR) has laid out an algorithm for RT-PCR (a method for detection of Zika virus ) testing based on clinical history.
As per the ICMR algorithm, if samples test negative for dengue and chikungunya, patients should be tested for Zika virus through RT-PCR ; second, if a patient has not been tested for dengue and chikungunya, the patient should be tested and if found negative for both, the patient should be tested for Zika. The presence of the virus should be then confirmed by sequencing and isolation, the algorithm states.
Can a patient bitten by an Aedes mosquito suffer from both Zika and dengue?
In the last chikungunya outbreak in Delhi, AIIMS reported cases where patients suffered from both dengue and chikungunya. Similarly, in the recent past, cases have been reported where co-infection of dengue, chikungunya and Zika has been present.
Co-infection of ZIKV has already been reported: with dengue and chikungunya in Colombia and with dengue in French Polynesia and New Caledonia. In 2016, Colombia reported a case, where a pregnant woman was confirmed with confirmed triple co-infection due to dengue (DENV-2), chikungunya (Asian genotype) and Zika (Asian lineage) virus. Similarly, Zika virus and dengue (DENV -2) were isolated from a 26-year-old woman, who was travelling to Haiti and had developed fever, rash, arthralgias and conjunctivitis.
What is the impact of such co-infection on severity of the illness ?
At a recent conference, regarding co-infection in vector-borne infections, in AIIMS, the broad consensus was that the impact on severity of illness still needs to be investigated. It was, however, mentioned that the dengue virus can enhance the effects of Zika.