Zika Virus: A review
Arun K. Shanker
Zika virus (ZIKV) is a member of the virus
family Flaviviridae and the genus Flavivirus, transmitted by daytime-active
Aedes mosquitoes, such as A. aegypti. Its name comes from the Zika
Forest of Uganda, where the virus was first isolated in 1947, the first
isolated strain was Strain: MR 766 (Original) and classified as Flaviviridae, Flavivirus, it original source
was the blood from experimental forest
sentinel rhesus monkey in the Zika forest of Uganda, in 1947. This was deposited by J. Casals,
Rockefeller Foundation1. Zika virus is spread to people through
mosquito bites. The most common symptoms of Zika virus disease are fever, rash,
joint pain, and conjunctivitis (red eyes). The illness is usually mild with
symptoms lasting from several days to a week. Severe disease requiring
hospitalization is uncommon.
History of discovery and geographical route of
transmission
A brief history research gives us the following information - Sporadic
human cases were reported from the 1960s in Asia and Africa. The first reported
large outbreak occurred in 2007 on Yap Island, Federated States of Micronesia.
The largest known ZIKV outbreak reported started in October 2013 in French
Polynesia, South Pacific, a territory of France comprising 67 inhabited
islands; an estimated 28,000 persons (11% of the population) sought medical
care for the illness2. The geographical path of its spread is shown
in Fig.1.
It spread throughout Africa3, with the first live case
recorded in a human patient in Nigeria a decade later around 1960 (2). The outbreak only threw up around a dozen confirmed cases. In 1966, the
first case was confirmed in South East Asia, and in the late 1970s it was
documented in Pakistan, India, Malaysia and Indonesia (3). The first official
epidemic was on the isolated island of Yap, Micronesia, in 2007 (4). It
affected almost 200 members of the island’s small population, making it a
relatively major crisis. It hit French Polynesia in 2013, with a huge outbreak
of 35,000 cases (5). Some led to instances of Guillain-Barre syndrome and
paralysis, while recent retrospective research suggests there was also a
corresponding spike in microcephaly. In 2014, around the time of the football
World Cup, Zika arrived in northern Brazil (6). Some suggest it could have been
brought over during the World Canoeing Championships in Rio around the same
time, an event which involved a large number of Pacific Islanders. The
mosquito-borne Zika virus is spreading across the Americas, with reported cases
from the Southern Cone through the Andes and Central America to the United
States. The U.S. Centers for Disease Control and Prevention reported confirmed
cases in 24 countries as of January 26, 2016.1 With no commercially available
test to confirm infections, many countries are unable to assess the real reach
of the virus within their territories4,5. Zika virus disease has
been described as being similar to dengue fever and “usually relatively mild,
though – as with other viral infections – people with weakened immune systems
may suffer disproportionately. The World Health Organization (WHO) has noted an
increasing body of evidence pointing to a link between the Zika virus and
microcephaly 6 in infants. As of late October 2015, Brazil has
reported 270 confirmed cases of microcephaly as well as 4,180 suspected cases.
 |
|
Fig. 1 History of Zika
Virus spread
|
Presence of Zika and Areas of Zika
Prior to 2015, Zika virus outbreaks
have occurred in areas of Africa, Southeast Asia, and the Pacific Islands. In
May 2015, the Pan American Health Organization (PAHO) issued an alert regarding
the first confirmed Zika virus infections in Brazil.
Fig.
2. Geographical
areas with active transmission
Currently, outbreaks are occurring in many
countries7. Zika virus will continue to spread and it will be
difficult to determine how the virus will spread over time. No locally
transmitted Zika cases have been reported in the continental United States, but
cases have been reported in returning travelers. Locally transmitted Zika virus
has been reported in the Commonwealth of Puerto Rico, the U.S. Virgin Islands,
and America Samoa. Following the FP outbreak in late 2013, there
were subsequent outbreaks in New Caledonia, the Cook Islands, and Easter Island8.The circulation of Zika
virus in the Pacific (Fig.3.): FSM (Federated States of Micronesia, 2007), FP
(French Polynesia, 2013/2014), NC (New Caledonia, 2014), CI (Cook Islands,
2014), EI (Ester Island, 2014).
 |
| Fig.3. Circulation of Zika virus in the Pacific. Source 8 |
Table 1 Countries with active Zika Virus
transmission. Source – CDC Atlanta
Americas
|
Oceania/pacific
islands
|
Africa
|
Barbados,
Bolivia, Brazil, Colombia, Commonwealth of Puerto Rico, US territory - Costa
Rica, Curacao, Dominican Republic, Ecuador, El Salvador, French Guiana, Guadeloupe,
Guatemala, Guyana, Haiti, Honduras, Jamaica, Martinique, Mexico, Nicaragua, Panama,
Paraguay, Saint Martin, Suriname, U.S. Virgin Islands, Venezuela
|
American
Samoa, Samoa Tonga
|
Cape
Verde
|
Transmission
methods
Zika virus is transmitted to people primarily
through the bite of an infected Aedes species mosquito (A. aegypti and A.
albopictus). These are the same mosquitoes that spread dengue and
chikungunya viruses 9. These mosquitoes typically lay eggs in and
near standing water in things like buckets, bowls, animal dishes, flower pots
and vases. They prefer to bite people,
and live indoors and outdoors near people. Mosquitoes that spread chikungunya,
dengue, and Zika are aggressive daytime biters. They can also bite at night. Mosquitoes
become infected when they feed on a person already infected with the virus.
Infected mosquitoes can then spread the virus to other people through bites. A
mother already infected with Zika virus near the time of delivery can pass on
the virus to her newborn around the time of birth, but this is rare. It is
possible that Zika virus could be passed from a mother to her baby during
pregnancy 9. It is being studied as to how
some mothers can pass the virus to their babies. To date, there are no reports
of infants getting Zika virus through breastfeeding. Zika is also spread through infected blood or
sexual contact Spread of the virus through blood transfusion and sexual contact
have been reported.
Diagnosis
In most people,
diagnosis is based on clinical symptoms and epidemiological circumstances (such
as Zika outbreak in the patient’s area or trips to areas where the virus is
circulating).Blood tests can help to confirm the diagnosis. Some (virological
PCR tests) are useful in the first 3-5 days after the onset of symptoms, while
others (serological tests) detect the presence of antibodies but are useful
only after five days. Once it has been demonstrated that the virus is present
in a given area or territory, confirmation of all cases is not necessary, and
laboratory testing will be adjusted to routine virological surveillance of the
disease9
Difference between Zika, dengue, and
chikungunya
All these diseases present similar symptoms,
but certain symptoms suggest one disease or another: Dengue usually presents
with higher fever and more severe muscle pain. There can be complications when
the fever breaks: attention should be paid to warning signs such as bleeding. Chikungunya
presents with higher fever and more intense joint pain, affecting the hands,
feet, knees, and back. It can disable people, bending them over so that they
cannot walk or perform simple actions such as opening a water bottle. Zika does
not have clearly characteristic features, but most patients have skin rashes
and some have conjunctivitis9.
Symptoms and Treatment
About 1 in 5 people infected with Zika virus
become ill (i.e., develop Zika). The most common symptoms of Zika are fever,
rash, joint pain, or conjunctivitis (red eyes). Other common symptoms include
muscle pain and headache. The incubation period (the time from exposure to
symptoms) for Zika virus disease is not known, but is likely to be a few days
to a week. The illness is usually mild with symptoms lasting for several days
to a week. People usually don’t get sick enough to go to the hospital, and they
very rarely die of Zika. Zika virus usually remains in the blood of an infected
person for about a week but it can be found longer in some people10.
There is no vaccine to prevent or specific medicine to treat Zika infections,
there reports from India that two candidate vaccine is being developed11.
Treat the symptoms: Get plenty of rest. Drink
fluids to prevent dehydration. Take medicine such as acetaminophen to relieve
fever and pain. Do not take aspirin and other non-steroidal anti-inflammatory
drugs. If you are taking medicine for another medical condition, talk to your
healthcare provider before taking additional medication. If you have Zika,
prevent mosquito bites for the first week of your illness. During the first
week of infection, Zika virus can be found in the blood and passed from an
infected person to a mosquito through mosquito bites. An infected mosquito can
then spread the virus to other people.
Prevention
Prevention involves
reducing mosquito populations and avoiding bites, which occur mainly during the
day. Eliminating and controlling Aedes aegypti mosquito breeding sites
reduces the chances that Zika, chikungunya, and dengue will be transmitted. An
integrated response is required, involving action in several areas, including
health, education, and the environment. To eliminate and control the mosquito,
it is recommended to: Avoid allowing
standing water in outdoor containers (flower pots, bottles, and containers that
collect water) so that they do not become mosquito breeding sites. Cover
domestic water tanks so that mosquitoes cannot get in. Avoid accumulating
garbage: Put it in closed plastic bags and keep it in closed containers. Unblock
drains that could accumulate standing water. Use screens and mosquito nets in
windows and doors to reduce contact between mosquitoes and people. To prevent
mosquito bites, it is recommended that people who live in areas where there are
cases of the disease, as well as travelers and, especially, pregnant women
should cover exposed skin with long-sleeved shirts, trousers, and hats. Use
repellents recommended by the health authorities (and apply them as indicated
on the label) Sleep under mosquito nets12.
