This blog post was authored by David J. Hunter, Acting Dean of Harvard University’s T.H. Chan School of Public Health. Enroll in his course, Readings in Global Health, to join the conversation about the Zika virus and other challenges in global health.
Many of you have had questions about the Zika virus; here is an update of what we know.
Zika virus was first identified in the blood of a rhesus monkey in the Zika Forest in Uganda in 1947. Like dengue, it is mainly transmitted to humans by mosquitoes. In a description of an outbreak in Yap Island, in Micronesia in 2007, the disease was described as mild1. While the major mode of transmission is by mosquitoes, it appears the virus may also be transmitted sexually, according to a published case report2 and a recent case under investigation in Dallas. Zika virus may also be transmitted through the blood supply or in utero.
An outbreak of the virus was reported in northeast Brazil in early 2015. In September 20153 a higher than usual frequency of babies born with microcephaly (abnormally small heads) was reported from this region. Epidemiologic studies are ongoing and suggest a link between Zika virus infections and cases of microcephaly, a link strengthened by the finding of Zika virus in amniotic fluid and the brain. It is unclear why cases of microcephaly have not been previously reported in connection with Zika virus infection in other regions. Zika virus infection has also been linked with cases of Guillain-Barre Disease, an autoimmune disease that causes muscle weakness and is often preceded by an infection.
On Monday, February 1st, the World Health Organization declared that the outbreak was a Public Health Emergency of International Concern, only the fourth time they have made such a declaration.
The virus has spread to more than 20 countries in Latin and Central America.
In the absence of a vaccine or any specific treatment for the infection, and given that many infected persons do not know they are infected, the main response is to diminish mosquito populations in order to reduce transmission probability. The main vector, the aedes aegypti mosquito, can reproduce in very small volumes of water, such as those that collect in tires, empty bottles or cans, and other habitats typical of urban environments. A multisectoral effort is needed to reduce these habitats in affected communities and spray insecticides to kill mosquitoes. A new technique, release of genetically modified male mosquitoes whose progeny will die, is being piloted in some areas; this technique is controversial as there are few examples of genetically modified insects being introduced into the wild.
Several countries have advised women not to become pregnant until the epidemic is contained. As many learners in my edX course, Readings in Global Health, have pointed out in the discussion boards, this advice may be futile in countries in which family planning services are minimally available. That countries have issued such advice indicates that there is a high level of concern about the long-term consequences of infection during pregnancy and the growing cohort of children with severe cognitive deficits.
Overall, this recent epidemic illustrates some of the weaknesses of disease surveillance in low- and middle-income countries. However, information about this virus has spread rapidly, and the basic epidemiologic facts were established within a matter of months. Why the devastating outcome of microcephaly has not been previously reported in association with Zika virus infection remains a mystery. Whether the outbreaks can be controlled by mosquito elimination and protection from mosquito bites remains to be seen. We had better hope so as no specific treatment or vaccine is currently available.
Join me in Readings in Global Health as we discuss the Zika virus and current issues and challenges in global health.
Duffy MR, Chen TH, Hancock WT, et al. Zika virus outbreak on Yap Island, Federated States of Micronesia. N Engl J Med. 2009;360(24):2536-2543.
Foy BD, Kobylinski KC, Chilson Foy JL, et al. Probable non-vector-borne transmission of Zika virus, Colorado, USA. Emerg Infect Dis. 2011;17(5):880-882.
Schuler-Faccini L, Ribeiro EM, Feitosa IM, et al. Possible Association Between Zika Virus Infection and Microcephaly – Brazil, 2015. MMWR Morb Mortal Wkly Rep. 2016;65(3):59-62.
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