The United States Awaits The Arrival of Home-Grown Zika Virus Disease
The Ebola outbreak in West Africa sensitized societies in Western Europe, the United States and elsewhere in the world to the potential threats that epidemic-prone diseases pose in this era of globalization. Fortunately, the appropriate authorities adhered to appropriate scientific and public health principles and were largely able to limit the spread of Ebola to the West African region. It was also clear that the West African Ebola outbreak would not be the last ‘exotic’ infection to test the public health systems of developing and more industrialized societies. Unlike Ebola, the latest ‘newcomer’, the Zika virus will continue to pose a threat to all communities that harbour its mosquito host, but by applying lessons learned from initial research efforts and adherence to public health principles, the consequences of this infection should be minimized.
The Zika virus is a member of the Flavivirus genus, which includes the viruses which cause yellow fever, dengue, West Nile virus infection, Japanese encephalitis, St. Louis encephalitis and tick-borne encephalitis. The virus was originally detected in 1947 in a caged monkey which had developed a febrile illness at a yellow fever surveillance station in the Zika Forest in Uganda. Subsequently, it was found that the infection was relatively common in equatorial Africa with up to 40% of certain populations showing serological evidence of previous exposure to the virus.
Human infection is now recognized as primarily through the bites of infected Aedes aegypti and albopictus mosquitos which have beenrecognized as the vectors for dengue and chikungunya fevers. Unlike those mosquitos that carry malaria, these mosquitos bite and feed during the daytime hours necessitating the need for indoor and outdoor neighbourhood insecticide spraying, covering exposed skin during the day and liberal use of personal insecticide sprays. Communities should also be encouraged to dispose of, or treat water-holding containers with a long-lasting larvicide prior to the mosquito season to reduce opportunities for mosquito multiplication. In addition, as a blood-borne infection, Zika virus can be transmitted by blood transfusion and it has also been recognized that a man with Zika can transmit the virus to his sex partner for many months after becoming infected because the virus is now known to persist in semen long after it has disappeared from his blood.
The most common symptoms of Zika virus infection are fever, rash, muscle and joint pains and conjunctivitis. However, these symptoms may be absent or very mild, lasting for several days to a week following an infected mosquito bite. As a result, many people may not realize they have become infected. Some evidence suggests lifelong immunity following natural infection, which means that reinfection, is highly unlikely. Although it is generally a very mild disease, the most severe consequence of Zika infection is the development of severe neurological conditions, including microcephaly, in neonates exposed to infection in pregnancy – particularly during the first trimester. In common with dengue and chikungunya fevers, Zika has also been associated with an increased incidence of Guillain-Barré syndrome (GBS). GBS is a rare autoimmune disease in which the patient’s immune system is triggered, often by a bacterial or viral infection, to attack peripheral nerves resulting in inability to feel pain, reduced or elevated temperature and touch sensitivity as well as loss of muscle tone. As a result of breathing difficulties, approximately one quarter of cases require intensive care. GBS can be fatal in 3-5% of cases.
Prior to 2015, outbreaks of Zika virus occurred in parts of Africa, Southeast Asia, and in the Pacific Islands. However, in May 2015, the Pan American Health Organization (PAHO) issued an alert regarding the first confirmed cases of Zika virus infection in Brazil. Subsequently outbreaks have been reported from many countries in the world – particularly from elsewhere in Latin America and the Caribbean Islands. As a result of the rapid spread of the infection, WHO subsequently declared Zika virus infection and its associated congenital and other neurological disorders as a Public Health Emergency of International Concern (PHEIC) in February 2016. The term PHEIC is defined in the International Health Regulations as “an extraordinary event which is determined to constitute a public health risk to other States through the international spread of disease and to potentially require a coordinated international response”.
As of 8 June 2016, WHO has reported that 60 countries have recorded mosquito-borne transmission of Zika of which 46 have experienced their first ever outbreak since 2015. A further 14 countries who, prior to 2015, had recorded evidence of mosquito-borne Zika virus transmission, continue to see new cases of the disease.
At the time of writing (14 June 2016), there have been 691 proven cases of Zika virus infection diagnosed in the United States. All of these, except one (a laboratory-acquired infection) have been linked to travel to Zika-endemic countries. Of these, 11 cases were among women whose infection was acquired as a result of sexual transmission from an infected male traveller who had recently returned from an endemic country. To date, there have been 206 confirmed cases of Zika virus infection diagnosed among pregnant women in the U.S. and the first cases of microcephaly associated with Zika have been detected. Two cases of Zika-associated GBS have also been diagnosed. While none of these cases acquired their infections as a result of an infected mosquito bite in the United States, the potential mosquito vectors are present in the majority of the southern and north eastern states. (see maps available at http://www.cdc.gov/zika/pdfs/zika-mosquito-maps.pdf).
It is clearly only a matter of time before mosquitos in the United States become infected with Zika virus and place the domestic population at risk. Until that happens, U.S. residents together with their counterparts in those countries outside those areas where Aedes mosquitos are known to be highly prevalent, which includes northern Europe and South Africa, should take appropriate precautions when visiting endemic regions of the world (see http://www.cdc.gov/zika/geo/active-countries.html) including visits to the forthcoming Olympic Games in Rio de Janeiro.
In order to prevent serious adverse pregnancy outcomes, both CDC and WHO recommend that women who are of childbearing age and who wish to become pregnant delay travel to endemic regions or continue to use barrier contraceptive devices such as condoms. There is no justification for others to delay or postpone travel.
However, both WHO and CDC have issued guidelines to prevent sexual transmission of Zika among those that have been exposed to infection. The current WHO guidelines are listed below:
1.Country health programmes should ensure that:
a) All people (male and female) with Zika virus infection and their sexual partners (particularly pregnant women) receive information about the risks of sexual transmission of Zika virus, contraceptive measures and safer sexual practices, and are provided with condoms.
b)Women who have had unprotected sex and do not wish to become pregnant due to concerns about Zika virus infection have ready access to emergency contraceptive services and counselling.
c)In order to prevent adverse pregnancy and fetal outcomes, men and women of reproductive age, living in areas where local transmission of Zika virus is known to occur, be correctly informed and oriented to consider delaying pregnancy; and follow recommendations (including the consistent use of condoms) to prevent human immunodeficiency virus (HIV), other sexually transmitted infections, and unwanted pregnancies.
2.Sexual partners of pregnant women, living in or returning from areas where local transmission of Zika virus is known to occur, should practice safer sex or abstinence from sexual activity for at least the whole duration of the pregnancy.
3.Couples or women planning a pregnancy who are returning from areas where transmission of Zika virus is known to occur, are strongly recommended to wait at least 8 weeks before trying to conceive to ensure that any possible Zika virus infection has cleared; and 6 months if the male partner was symptomatic.
4.Men and women returning from areas where transmission of Zika virus is known to occur should adopt safer sex practices or consider abstinence for at least 8 weeks upon return.
a)If before or during that period Zika virus symptoms (rash, fever, arthralgia, myalgia or conjunctivitis) occur, men should adopt safer sex practices or consider abstinence for at least 6 months. Women should be correctly informe
b)WHO does not recommend routine semen testing to detect Zika virus. However, symptomatic men can be offered semen testing at the end of the 8 week period after return, according to country policy.
5.Independently of considerations regarding Zika virus, WHO always recommends the use of safer sexual practices including correct and consistent use of condoms to prevent HIV, other sexually transmitted infections and unwanted pregnancies.
WHO states that it is likely that Zika virus infection will continue to spread globally and that it will be difficult to determine how and where the virus will spread over time. While there is no protective vaccine or antiviral medicine effective against the virus, the rate of spread, geographical distribution and number of cases of disease complications in both neonates and adults will largely depend upon population awareness, on resources made available for mosquito control and the spread and uptake of information regarding sexual transmission of the virus.