Zika virus infection

Zika virus (ZIKV) belongs to the flaviviridae family  has derived its name from the Zika (means ‘overgrown’ in Luganda language)forest near lake Victoria,  Uganda where it was first identified in 1947 in rhesus monkey through a monitoring network of sylvatic yellow fever. Subsequently it was identified in humans in 1952 in Uganda, and Nigeria.

The infection is known as Zika fever. It may remain asymptomatic or may cause only mild symptoms. It was known to be restricted to a narrow equatorial belt from Africa to Asia since 1950s. The virus spread to French Polynesia and then to Easter island across Pacific ocean in 1914 and in 2015 to Mexico, central America, Caribbean islands and South America with an epicenter in Brazil where the Zika outbreak assumed a pandemic proportion. World Health Organization has declared Zika virus disease to be a Public Health Emergency of International Concern (PHEIC) on 1st February, 2016.

Since India provides fertile climate for the Aedes egypti mosquito to grow and multiply, there is the potential of an outbreak situation in the country.³ laboratory-confirmed cases of Zika in  January 2017 from Bapunagar, Ahmedabad, Gujarat were reported in May 2017. Later in the same year in July, there were reports of Zika infection from Krishnagiri, Tamil Nadu and one man tested positive for the virus. An elderly women was diagnosed with Zika infection in September 2018  at Jaipur, Rajasthan. Since then 152 more individuals including 22 pregnant women have tested positive for the infection around Shasti nagar area and Sindhi camp area...More than 100 persons have been  tested positive for the Zika virus in seven districts of Madhya Pradesh. This includes 44 cases reported from Bhopal, 20 from Sehore, 29 from Vidisha, two each from Sagar and Hoshangabad, and one each from Narsinghpur and Raisen. With the presence of these confirmed cases, India has been included in WHO category.² The spread appears to be due to local transmission and none of the patients were associated with travel history. It suggests that ZIKV might be present in India since long time.¹

Zika virus is related to Dengue, Yellow fever, Japanese encephalitis (JE) and West Nile fever (WNF). It is a non-segmented, single stranded RNA virus.  The viral particles are 40 nm in diameter with an outer envelope and a dense inner core. It is an icoshedral virus of 18-45 nm in diameter. Zika virus causes a zoonosis of the monkeys. Mosquitoes transmit the disease to humans.  It is transmitted by day-time active Aedes mosquitoes (A aegypti, A albopictus).²

Aedes aegytpi forms the principal vector supported by secondary vector Ae albopictus. Ae aegypti is a native of Egypt, commonly known as yellow-fever mosquito. Ae albopictus is identified by its peculiar white-spotted body and legs, and it has been given the name, tiger mosquito.  The mosquito is found in urban surroundings in domestic and peri-domestic areas.

The flight of mosquito is short. It is highly domestic and breeds near human habitat in standing water collected in containers such as old discarded tyres, cans, water storage jars, mud pots, plastic containers, abandoned shoes, coconut shells, uncovered overhead tanks, oil drums, drip-pans below refrigerators, air conditioners, empty tins, plastic containers, plastic trays under potted plants, water coolers, pots, latex collecting cup, and buckets (man-made habitats). It has a flight range of only 100-200 m. It mostly rests indoors, though it could be in any cool shaded places inside or outside the house.

The female mosquito gets infected by Zika virus while feeding human blood having Zika infection. Peculiarly the mosquito is a daytime feeder and it bites many people to get its blood meal. It has a diurnal feeding pattern usually peaking mid-morning and late afternoon. Peculiarly its bite is imperceptible. It is capable of biting many people in a short period of time for one blood meal. Persons who stay indoors during the daytime are vulnerable to mosquito bites. Overcrowding, poor living conditions and lack of vector control facilitate the spread of infection. Epidemics are explosive.

There is a possibility of virus being transmitted sexually.³ Zika virus RNA has been detected in amniotic fluid and virus crosses the placenta and infect foetus.  It can be transmitted through blood transfusion, organ transplantation and laboratory exposure. There is a possible link between Zika and microcephaly in new born babies by motherto-child transmission.^4,5 There is likelihood of occurrence of miscarriages. The infected adults may present with neurological condition like Guillain-Barre syndrome (GBS).⁶ The Governments of Columbia, Dominican Republic, Equator, El Salvador, Jamaica, and Center for Disease Control and Prevention (CDC),US have issued guidelines about precautions for women to postpone travel and even to postpone getting pregnant.⁷

Many infected persons remain asymptomatic. About 1 in 5 people infected with Zika become ill. The incubation period is not known but it likely to be a few days to a week.

The illness is usually mild with symptoms lasting for several days to a week. The most common symptoms are fever, rash, joint pain, and conjunctivitis. Other common symptoms include muscle ache and head ache. Thus the clinical features are non-specific.  It should be noted that occurrence of rash, and conjunctival hyperaemia are more common with Zika compared to other viral illnesses.  Zika virus usually remains in the blood of an infected person for about a week. The symptoms are similar to Dengue and Chikungunya which spread through the same mosquitoes that transmit Zika.

The symptoms are usually self-limiting. However the potential terratogenic and neurological complications are causing great concern. Terratogenic neurodevelopmental abnormalities may occur during the first two trimesters. The incidence of microcephaly may be as high as 1 per cent of pregnancies. In addition there may be occurrence of limb weakness, hearing deficits, ocular and skeletal abnormalities, cessation of development and cognitive and learning defects.⁸ In infected adults there is likelihood of development of Guillain-Barre syndrome and acute demyelinating encephalomyelitis.

The infection with Zika virus may be suspected based on symptoms with residence or visit to an area which is known to be endemic. The manifestations of Zika infections simulated those of Dengue and Chikungunya infection. Fever and arthralgia are common in Chikungunya and Zika infections. Myalgia is noted in Dengue, Chikungunya and Zika infections. Conjunctivitis is noted in Zika infection. Occurrence of low platelet count is noted in Dengue. Zika virus diagnosis can only be confirmed by laboratory testing for presence of Zika virus RNA in the blood or other body fluids such as urine or saliva. RT-PCR appears to be the best way way of assay. Zika-specific IgM can be demonstrated 3-7days following the clinical manifestations, and IgG by the end of second week of illness.  The former persists up to 3 months and the latter for months to years. The limitation of these tests should be remembered as the current tests for Zika IgM and IgG cannot reliably distinguish between Zika and Dengue infections.⁹

Physicians in the Crop-Sprayed Towns in Brazil have put forward the theory that malformation of the skull and brain in children from pregnant women living in areas must be the effect of the pesticide, Pyriproxyfen which has been introduced into the drinking water supply. Pyriproxyfen is a chemical larvicide producing malformations in the developing mosquitoes by acting as a juvenile hormone (juvenoid).

There is no specific treatment. The patients who have presented with mild features of Zika virus infection  are to be treated with bed rest under mosquito net, antipyretic (acetaminophen, paracetamol) and fluid replacement either orally or intravenously to prevent dehydration. Administration of aspirin or non-steroidal antiinflammatory drugs may be considered only after ruling out the condition of dengue fever.

The patient must be prevented from mosquito bites. The patient is able to transmit the virus to a biting mosquito during the first week of illness. An infected mosquito can then transmit the virus to other people.

Vector control is essential in the prevention of Zika virus infection. The environment must be free of potential breeding sources. The containers such as old tyres, cans, jars, coconut shell, oil drums, pots and buckets, should not be left outside home as they can be filled with water and become breeding sites. Public health authorities should undertake fogging operations on war footing, and clear the breeding grounds of mosquito.

The best way of prevention of the infection is by protection against mosquito bites. Insect repellents are to be used and persons are advised to wear long sleeves and pants treated with permethrin. Lemon grass oil is given to poor pregnant women to help preventing them from getting bitten by mosquitoes. Lemon grass oil acts as a mosquito/ insect repellent. It is advised to secure screens on windows and doors to keep mosquitoes out. The human cost of the disabling disease is very great and public health services have to respond to the challenge.

Zika virus can spread from a pregnant woman to her foetus. Pregnant women in any trimester should consider postponing travel to any area where Zika virus infection is spreading. Unprotected sexual contact is discouraged.

India is the first country in the world to have ready for testing of two vaccines against the virus that is causing nightmares in The Americas. A single dose vaccine has been prepared by Bharat Biotech which is ready for pre-clinical trial. The vaccine may be a ‘recombinant’ vaccine produced through recombinant DNA technology by inserting a bacterial surface protein to stimulate an immune response. or an ‘inactivated’ vaccine where virus is killed by chemicals, heat or radiation, is incapable of reproduction but can still trigger a more stable and safer immune response.