The Zika virus (ZIKV) infection has raised alarms in many countries because of its “explosive spread” in Central and South America. The Health Ministry has recently stated that Malaysia is also vulnerable to the spread of the infection.
ZIKV is a member of the Flaviviridae family and is related to the viruses that cause the dengue, Japanese encephalitis and chikungunya infections.
It is transmitted through the bites of infected Aedes aegypti and Aedes albopictus mosquitoes – the same mosquitoes that transmit dengue. It can also be transmitted from mother to foetus.
The infection was first detected in the Zika forest in Uganda in 1947 from which it spread to Asia, the Pacific islands, and more recently, Central and South America.
The initial outbreaks occurred in Micronesia in 2007 and French Polynesia in 2013.
ZIKV was isolated from Aedes aegypti mosquitoes in Bentong, Pahang, more than four decades ago (Source: Marchette NJ, Garcia R, Rudnick A. Am J Trop Med Hyg. 1969;18:411–5).
An acute infection was reported in September 2014, in a traveller who had returned to Heidelberg, Germany, six days after a three-week vacation in peninsular Malaysia and Sabah (Source: Tappe et al. Emerg Infect Dis. 2015 May; 21(5): 911–913).
The Health Ministry announced to the media that 288 samples from patients who tested negative for dengue analysed so far have been negative for the Zika virus (Source: kpkesihatan.com, accessed Jan 30, 2016).
Features of infection
After a bite from an infected mosquito, the first symptoms develop in three to 12 days, but it can be shorter or longer.
In general, direct human-to-human transmission does not occur. However, there is evidence suggesting sexual transmission through semen can occur.
ZIKV can be transmitted by blood transfusion, but standard precautions for safe blood donations and transfusions should prevent this.
Many of those infected do not have any symptoms. Symptoms occur in about one in five of those infected, and are usually mild, lasting two to seven days.
The commonly reported symptoms include acute fever with rash, joint pains (arthralgia), conjunctivitis, muscle aches (myalgia) and headache.
The symptoms are similar to that of dengue and chikungunya infections, which are also transmitted by Aedes mosquitoes found in the same geographical areas.
There are currently no commercially-available test kits. Tests are carried out in public sector facilities with the primary test being reverse transcription polymerase chain reaction (RT-PCR).
Antibody testing is less reliable because of cross-reaction with infections by similar viruses, e.g. dengue.
There is no specific treatment, and most infections require no treatment.
Troublesome symptoms are treated with plenty of rest; adequate fluid intake; and management of fever and pain.
There is strong suspicion that ZIKV is associated with microcephaly and Guillain Barre syndrome (GBS).
Brazil has reported an extraordinary outbreak of microcephaly, a rare condition in which newborns have abnormally small heads and brains.
There is a temporal association in that the increase in microcephaly occurred within nine months of the ZIKV outbreak in northern Brazil.
Since October 2015, the microcephaly rate has been about 300 in every 100,000 live births, compared to 5.7 in every 100,000 live births in 2010.
Although inconclusive, there is strong suspicion that ZIKV is the causative agent.
ZIKV can cross the placental barrier and has been detected in the blood and tissues of affected foetuses/newborns. It is likely that infection in early pregnancy poses the greatest risk.
Brazil, El Salvador and Venezuela have reported cases of GBS in individuals with ZIKV symptoms.
GBS is a rare and serious condition in which the body’s immune system attacks part of the peripheral nervous system.
Needless to say, there are many other causes of microcephaly and GBS.
Preventing bites by infected mosquitoes is crucial. This involves protecting oneself and keeping the mosquito population down. The same measures apply to dengue.
Individual protection include being aware of one’s environment; using mosquito repellents, even when indoors; wearing long-sleeved shirts, trousers, socks and shoes when outdoors; using air-conditioning, if available; ensuring window and door screens are secure and have no holes; using mosquito nets if sleeping areas are not screened or air-conditioned; and seeking medical attention early when sick.
If someone in the home gets the infection, there has to be extra vigilance.
The mosquito(es) that bit the infected person can spread the infection to others in the same vicinity.
The mosquito population can be reduced by getting rid of breeding sites, which include all places that collect rain and where water is stagnant.
Inspecting one’s environment daily for stagnant water, and taking simple measures like turning over or covering all water storage containers; clearing blockages in drains and gutters; and changing water in household containers on alternate days, are essential.
While individual efforts are important, they do not count much if societal or governmental efforts are minimal.
More effective, innovative and sustained efforts from the Health Ministry and other governmental agencies are urgently required to prevent not only ZIKV, but also dengue.
Pregnancy and sex
Knowledge about ZIKV is limited and is still evolving.
Interim guidelines issued by various regulatory and professional organisations include:
• Pregnant women should avoid travel to countries with ongoing outbreaks, i.e. those with locally-acquired cases reported in the last six months. The affected countries can be found at www.cdc.gov/zika/geo/.
• Those who must travel, or choose to travel, to such countries should take all necessary precautions to minimise the chances of mosquito bites.
• Pregnant women recently returned from countries with ongoing outbreaks should inform their obstetrician, midwife or family doctor for monitoring and/or testing.
• Pregnant women with a history of travel to a country with ongoing outbreaks and who present with symptoms consistent with ZIKV disease during or within two weeks of travel, should be tested for ZIKV infection and other travel-associated infections.
Where ZIKV is identified upon laboratory testing, a referral to a foetal medicine service should be made for further assessment.
If the test for ZIKV is negative, serial (four-weekly) foetal ultrasound scans should be considered, to monitor foetal growth and anatomy.
Testing for ZIKV is not recommended for those whose symptoms have resolved by the time of presentation, but they too should be offered serial (four-weekly) foetal ultrasound.
Routine testing of those with no symptoms while travelling, and for two weeks after their return from an affected country, is not recommended.
However, serial foetal ultrasound scans should be considered, as most ZIKV infections have minimal symptoms.
• Anyone in whom foetal microcephaly, i.e. head circumference more than two standard deviations below the mean for gestational age, or brain abnormality, e.g. intracranial calcifications, is diagnosed on ultrasound, and who has previously visited an affected area during pregnancy, should be referred to a foetal medicine service for further assessment.
Women with a diagnosis of foetal microcephaly or intracranial calcifications, but who have not travelled to an affected area during pregnancy, do not need to be tested.
If foetal microcephaly or a brain abnormality is diagnosed, an amniocentesis to test for ZIKV should be considered.
• Women should avoid becoming pregnant while travelling in a country with ongoing outbreaks.
On returning home, they should avoid becoming pregnant for a further 28 days, i.e. a maximum two-week incubation period and possible two-week viraemia.
• If a woman’s sexual partner has travelled to an affected country, effective contraception is advised and includes condom use to prevent sexual transmission for 28 days after his return home if he had no symptoms, either whilst abroad or within two weeks of his leaving the affected country, or for six months following recovery if he has symptoms during that period.
Dr Milton Lum is a member of the board of Medical Defence Malaysia. This article is not intended to replace, dictate or define evaluation by a qualified doctor. The views expressed do not represent that of any organisation the writer is associated with.