Kaushik Bharati, PhD
Zika virus (ZIKV) has recently hit the news headlines in conjunction with a sharp rise in the birth of deformed babies in Brazil. These babies, at least 2,782 in number in 2015 alone (New York Times News Service, December 31, 2015), are born with abnormally small brains, technically termed as microcephaly. Many of these children do not survive; but those who do, face impaired intellectual development for the rest of their lives. The crisis is so severe that health officials have declared a state of public health emergency in the country and have even advised childbearing age couples to postpone any plans for pregnancy until the crisis settles down.
Epidemiological evidence supports that the microcephaly outbreak in Brazil is due to infection with ZIKV that is spread by the bite of infected Aedes aegypti mosquitoes. More direct evidence is now available (New York Times News Service, January 15, 2016), as ZIKV has been found in tissues of four Brazilian infants, two of whom had microcephaly and died soon after birth, while the other two died in utero.
ZIKV is so called because it was first reported from the Zika forest in Uganda (1947), where it was isolated from a rhesus monkey. The first isolation from human patients was in 1968 in Nigeria. Since then it has largely remained confined to Africa with few outbreaks occurring in Asia. A major epidemic occurred in 2007 in the island of Yap in Micronesia, where nearly three quarters of the population were infected. In 2014, ZIKV was reported on Easter Island. In March, 2015 Brazil reported cases of ZIKV, and since October, 2015, 16 other countries and territories of tropical Latin America and the Caribbean also reported the spread of the virus. As indicated above, the disease has reached epidemic proportions in Brazil, with the birth of nearly 3,000 babies born with microcephaly.
ZIKV belongs to the Flaviviridae family of arboviruses to which other viruses like Yellow Fever, Dengue, Japanese encephalitis, West Nile, St. Louis encephalitis, also belong. The structure of ZIKV exhibits an icosahedral symmetry, and consists of a non-segmented, positive sense, single-stranded RNA genome, surrounded by a capsid protein layer, with an outer envelope consisting of a lipid bilayer with the envelope protein.
Transmission and Symptoms
The mode of transmission of ZIKV is by the bite of an infected Aedes aegypti mosquito in the skin, where it infects the dendritic cells of the skin, namely the Langerhans cells. The virus then spreads to the draining lymph nodes and subsequently to the blood, thereby spreading to other parts of the body. The virus has an incubation period of up to a week.
The most common symptoms of ZIKV infection include mild fever, skin rashes, conjunctivitis, muscle & joint pain, and general body ache. The disease is generally self-limiting and resolves after a week or so. There is currently no evidence that ZIKV can cause death, although a few deaths have been reported in isolated cases, where there was evidence of pre-existing disease conditions
Diagnosis is generally based upon clinical examination within an epidemiological context of disease transmission. Epidemics of ZIKV infection warrant that laboratory confirmation be carried out by either molecular methods, such as detecting viral genes by Polymerase Chain Reaction (PCR) tests or by serological methods, by detecting antibodies such as IgM by the Enzyme-linked Immunosorbent Assay (ELISA).
There are no specific drugs available for the treatment of ZIKV infections. Neither are there any vaccines available for prevention of the disease. Treatment is symptomatic, with the aim of controlling the fever, relieving pain and discomfort of the patient until the disease resolves. The patient is also advised to take rest and drink plenty of fluids.
Vector control remains the mainstay for prevention of ZIKV transmission. Wherever the Aedes aegypti mosquitoes breed, need to be destroyed. Since this mosquito also spreads Dengue and Chikungunya, the control measures are essentially the same.
The following measures are to be adopted in order to prevent outbreaks of ZIKV infections in humans:
• All roof-top water tanks should remain covered at all times, and should be emptied and cleaned at regular intervals.
• All containers where water is kept or can accumulate should be emptied regularly. These include flower vases, water containers, coolers, coconut shells, tyres etc.
• Avoid accumulating garbage; dispose all garbage in closed plastic bags.
• Use mosquito nets in the windows. Note that Aedes aegypti is a daytime biter. Therefore, use of mosquito bed nets at night will likely be unnecessary.
• You should cover all exposed parts of the body while outdoors. These include, wearing full-sleeved shirts, trousers, socks and boots.
• You can also use mosquito-repellent creams to prevent mosquito bites
The recent spate of ZIKV outbreaks in many parts of tropical Latin America and the Caribbean indicates that the virus has spilled-over to the human population, and that the virulence of the virus could increase in the long-run. Moreover, with rising global temperatures, as a result of Global Warming the geographical range of the vector mosquito is likely to increase. The occurrence of microcephaly in babies and infants is most unfortunate and should be managed on a “war-footing”.
The Centers for Disease Control and Prevention (CDC), Atlanta, USA has issued a travel alert (http://www.cdc.gov/media/releases/2016/s0315-zika-virus-travel.htm dated January 15, 2016) for people traveling to regions and certain countries where ZIKV transmission is ongoing. These include the following:
• El Salvador
• French Guiana
• Puerto Rico.
This CDC alert is particularly important for pregnant women, who should avoid travelling to countries where ZIKV transmission is occurring, at least until this public health crises resolves. This might appear to be a drastic step, but it is a step in the right direction, as this will prevent babies being born with microcephaly and other associated complications.