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| photo by CDC PHIL, Aedes Mosquito |
New European Center for Disease Control ( ECDC) risk assessment is currently evaluating a possible
link between the observed increase of congenital microcephaly in Brazil
and Zika virus (ZIKV) infection.
Until recent months Zika virus was not widely associated
with microcephaly.
According to CDC, in the past four months, microcephaly
cases in Brazil
rocketed to 3,500 from 147, the average for the same time last year (2014). About 46 babies have died due to birth
defects.
The link was first detected when Brazilian health
authorities found traces of the Zika virus in a deceased infant born with
microcephaly or in amniotic fluid of mothers delivering microcephalic infants.
The first confirmed cases of ZIKV infection in Brazil
were reported in May 2015.
Transmission of the virus in Brazil is likely to have started
several months before because the disease is new and mild, and could have been
unrecognised or misdiagnosed, as dengue and chikungunya epidemics were ongoing.
Microcephaly caused due to any infection is usually caused
by transplacental infections occurring early in pregnancy and is only detected
during the second half of pregnancy or after birth.
The observed six months delay between the recognition of the
transmission of ZIKV in May 2015, and the detection of an increase in
microcephaly in November 2015, is therefore compatible with a temporal
association between the two events.
Currently there is only ecological evidence of an
association between the two events, due to sudden epidemic of microcephalic
babies born and clustered around a specific time period.
A possible causative association cannot be ruled out but
further investigations and studies are needed to understand the association and
the possible role of other factors, states the ECDC risk assessment.
In November the Brazilian Ministry of Health declared a
public health emergency in relation to an unusual increase in the number of
children born with microcephaly in 2015.
In addition to Brazil's findings, French
Polynesian health authorities have also reported an unusual increase in autoimmune
and central nervous system malformations in babies born during a Zika virus
outbreak on the islands from 2014 to 2015. (73 cases, 42 of them being
Guillain-Barré Syndrome, in a population of about 270 000).
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| CDC map illustrates areas affected or possibly affected by the spread of Zika virus |
Zika virus disease is a mosquito-borne viral disease caused
by Zika virus (ZIKV), a flavivirus from the Flaviviridae family and is
primarily transmitted through the bite of infected Aedes mosquitoes.
The virus was first identified in 1947 in the Zika forest in
Uganda
in the rhesus Macaque population and have two main lineages, the African
lineage and the Asian lineage.
Prenatal or perinatal complications of ZIKV infections have
not been described in the literature. There is some evidence that perinatal
transmission can occur, most probably transplacental or during the delivery of
a viraemic mother. However, materno-foetal transmission has been demonstrated for
several other Flaviviruses (dengue, West Nile
fever).
Some other Flavivirus infections are known to have the
potential to cause premature birth, congenital defects and microcephaly.
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.
Meanwhile, Brazilian officials are also reporting neurologic
complications in other Zika virus patients, primarily Guillain-Barre syndrome,
which has also been seen in French Polynesian patients who had suspected
infections. "Although neither even establishes a causal relation with Zika
virus, the hypothesis cannot be ruled out," says a health official in Brazil.
In conclusion, a causative association between microcephaly
in newborns and ZIKV infection during pregnancy is plausible, but not enough
evidence is available yet to confirm or refute it. Many studies are needed
before a definite conclusion can be reached.
There is no vaccine to prevent infection or medicine to
treat Zika virus.
Meanwhile, CDC issues a travel advisory to pregnant
women to consider postponing travel to
areas where Zika virus transmission is ongoing.
References:
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