and well-being of children and youth
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Zika is a flavivirus (like West Nile, Dengue, Japanese encephalitis, St. Louis encephalitis and yellow fever viruses) and was first detected in Uganda’s Zika forest in 1947.
Zika virus is primarily spread by the bite of Aedes aegypti (and possibly Aedes albopictus) mosquito. Aedes bite primarily for a few hours after sunrise and before sunset. Zika virus has also been transmitted through semen. Since there is a viremic phase, blood transfusion is another probable source of infection.
Most infected people (75-80%) are asymptomatic. Common symptoms are maculopapular rash (which is sometimes pruritic), fever, muscle aches, and non purulent conjunctivitis. Most patients recover completely within a few days.
Diagnosis is by:
Serology becomes positive about five days after symptom onset but may cross-react with other flaviviruses such as Dengue. This can often be sorted out by specialized testing (using a plaque reduction neutralization test or PRNT). Molecular testing for virus detection is usually only positive in the blood during the first 7 days of infection but there are cases where it was positive for many weeks. Urine usually stays positive by molecular testing for longer than does blood.
Zika virus was first recognized in the late 1940s, when it was isolated from a primate and Aedes mosquitoes in Uganda. Since then, there have been sporadic human cases in Africa. Spread to Asia was documented in humans in the 1970s, Guam and Micronesia in 2007, Tahiti and French Polynesia in 2013, New Caledonia, and to the Cook Islands and Easter Island in 2014. The virus was first detected in Brazil in May 2015, and locally-acquired cases have now been documented in many countries in South America, the Caribbean, and Mexico (see http://www.cdc.gov/zika/geo/index.html).
Previous outbreaks were not widely publicized as there was minimal apparent morbidity, although a possible link to Guillain-Barré syndrome was noted in French Polynesia.
Most experts now believe that Zika virus is the cause of an unusual cluster of microcephaly in the northeast region of Brazil. Prior to 2015, there were 130 to 170 cases of microcephaly annually in Brazil. Over the past year, there have been over 4,000 cases of microcephaly, largely concentrated in parts of the country with the largest number of cases of Zika virus infection. Zika virus has been detected in amniotic fluid from a small number of pregnancies with microcephalic infants and from the brains of infants who died, demonstrating that the virus can cross the placenta and infect the baby. Many of the infants with microcephaly have other brain anomalies including intracranial calcifications. They commonly also have abnormalities outside the central nervous system including redundant scalp skin, arthrogryposis, and clubfoot, all of which are somewhat unusual in children with microcephaly, suggesting a common etiology. Cases of affected fetuses have been described in women from temperate climates with travel to Zika-endemic areas in the first or early second trimester.
No other flavivirus is known to be teratogenic in humans. Microcephaly was not described in the previous outbreaks of Zika virus, but perhaps the current, much larger outbreak has simply allowed this relatively rare manifestation to be observed and there may be other risk factors involved. In retrospect, there may have been an increase in the incidence of microcephaly during the outbreak in French Polynesia, affecting approximately 1% of infants born to exposed pregnant women. Future observations on rates of microcephaly and other of brain defects in other Zika virus outbreak countries will confirm or refute this association, and pregnancy outcomes are being actively tracked in these countries.
Zika virus is also believed to be associated with an increased incidence of Guillain-Barré syndrome but the causal relationship is still being studied.
Because Zika virus infection is usually mild with no known sequelae, testing is currently not advised for symptomatic or asymptomatic children or youth. However, if they have a severe illness thought to potentially be Zika virus infection (Guillain-Barré syndrome, meningoencephalitis, etc.) with recent travel to a country with Zika virus, physicians should consult with their local virologist or infectious diseases physician to arrange testing.
There is currently no vaccine or treatment for Zika virus infection, but the incidence of morbidity outside of pregnancy is likely very low. The risk of complications and sequelae is thought to be higher with other viruses, including Dengue or chikungunya, which are spread by the same mosquito as Zika virus, and thus are circulating in the same countries. Travelers of all ages to areas where any of these viruses are present should use personal protective measures (i.e. clothing and mosquito repellents) to prevent mosquito bites.
Sexual transmission from males is possible weeks or even months following Zika virus infection. Although all cases to date involved men with symptoms of Zika virus infection, it is possible that spread can occur from asymptomatic men. Therefore, pregnancy should be avoided for up to 6 months when a male returns from a Zika endemic area. If the partner is already pregnant, condoms should be used until delivery.
If the infant born to a woman who travelled to a Zika endemic country during pregnancy has microcephaly or any other manifestations of congenital infection on prenatal ultrasound or on physical examination (intrauterine growth retardation, hepatosplenomegaly, petechiae, retinal abnormalities, cerebral calcifications, redundant scalp, arthrogryposis, clubfoot, etc.), the placenta and cord blood (if still available), cerebrospinal fluid (if obtained) and infant serum should all be tested for Zika virus. Maternal and infant serology should be performed. A paediatric infectious disease physician and a virologist should be consulted to arrange testing and to determine what other investigations are indicated for Zika virus. One should also investigate for other infectious and non-infectious causes of microcephaly.
Although Zika virus has been detected in breastmilk, it is not thought to be viable so breastfeeding is not contraindicated.
Currently Aedes mosquitoes have not been detected in Canada. There is no evidence that transmission has ever occurred to the Culex mosquito, which is present in Canada. Therefore, acquisition is only throught to be possible via sexual transmission or vertical transmission from a traveler to a country with Zika virus or from a blood transfusion.
Dr. Joan Robinson, principal author; reviewed by the CPS Infectious Diseases and Immunization Committee and the Board of Directors.
Disclaimer: The recommendations in this position statement do not indicate an exclusive course of treatment or procedure to be followed. Variations, taking into account individual circumstances, may be appropriate. Internet addresses are current at time of publication.