An examination of the scientific correlation between the zika virus and microcephaly.

1. The Zika Virus
& Microcephaly
Dr. Allen Cherer

2. Zika virus is an arthropod-borne flavivirus discovered
in Africa in 1947. When infected by the virus, most
persons are asymptomatic or demonstrate generally
mild, self-limited illness characterized by fever, rash,
arthralgia, and conjunctivitis. The first widespread
outbreak of the Zika virus was recognized on Yap
Island, Federated States of Micronesia, in 2007,
followed by outbreaks in Southeast Asia and the
Western Pacific, including a large outbreak in French
Polynesia in 2013-14.

3. Since the identification of the Zika virus
infection in Brazil in May, 2015, the virus has
spread rapidly throughout the Americas, and
as of February 2016, thirty-one countries and
territories had reported cases.

4. A bite of the Aedes aegypti mosquito is the main
route of exposure, but sexual, maternal-fetal, and
intrapartum transmission have all been
documented. To date, all cases reported in the
continental United States have been travel-
associated, whereas in the U.S. territories
(American Samoa, Puerto Rico, and U.S. Virgin
Islands), the vast majority of cases have been
locally acquired vector-borne.

5. Although infection with the Zika virus generally leads to
mild disease, its emergence in the Americas has
coincided with a marked increase in babies being born
with microcephaly, a neurological disorder present at
birth and defined as head circumference at least 2 SD
smaller than the mean for sex, age, and ethnicity and
with head circumference at least 3 SD smaller being
deemed severe. Congenital microcephaly is a condition
associated with a reduction in brain volume and is often
caused by genetic or environmental factors that affect
fetal brain development.

6. Prenatal viral infections, such as rubella and
cytomegalovirus, hypertensive disorders, and
maternal alcohol have also been associated
with the condition. Cases have been reported
after intrauterine infection with West Nile
virus (also a flavivirus) and Chikungunya virus.

7. Given the widespread nature of the Zika virus
epidemic in the Americas, the temporally
associated increase in microcephaly cases in
Brazil, and the retrospective findings of a
cluster of microcephaly and neurologic
disorders associated with the Zika virus in
French Polynesia, the WHO declared Zika
virus a Public Health Emergency of
International Concern on February 1, 2016.

8. In order to reduce the risk of microcephaly,
recommendations included avoidance of travel to
affected countries by pregnant and childbearing aged
women, use of condoms with partners returning from
affected countries, and pregnancy delay.
In order to better quantify the risk of microcephaly
associated with the Zika virus infection, a retrospective
study based on data from the completed Zika virus
outbreak in French Polynesia in 2013-14 was reported
in The Lancet by Simon Cauchemez, PhD, and
colleagues from the Institut Pasteur.

9. Based on four datasets providing information on all
cases of microcephaly, weekly number of
consultations for suspected Zika infection,
seroprevalence for Zika virus antibodies, and the
number of births during the outbreak, the
researchers developed a mathematical and
statistical model to illustrate the association
between the Zika virus and microcephaly and
demonstrated the risk for microcephaly to be
greatest during the first trimester of pregnancy.

10. According to the analysis, it is estimated that the risk
for microcephaly for mothers with the Zika virus
infection during the first trimester is about 1%.
Although the risk appears low compared to other
intrauterine viral infections (e.g., rubella,
cytomegalovirus), the incidence of the Zika virus
infection is very high during outbreaks (eg, 66% in
French Polynesia and 73% in the island of Yap).
Therefore, despite the relatively low fetal risk,
infection with the Zika virus is an extremely important
public health matter.
.

11. Dr. Allen Cherer
drallencherer.net