Zika virus (ZIKV), a member of the flavivirus family, was discovered in the Zika Forest of Uganda in 1947, subsequently diverged into two strains, and spread throughout Africa and Asia. Although it is believed to be endemic in these regions, its overall effects have been considered relatively benign, especially in comparison to other flaviviruses like dengue virus (DENV) and yellow fever virus (YFV). ZIKV is believed to have reached Brazil between June and August of 2014, although it may have arrived as early as between May and December 2013; by November 2014 doctors were reporting an increased incidence of cases with flu-like symptoms, and by March 2015 an increased incidence of microcephaly. These reports prompted an investigation into a possible association between ZIKV and microcephaly. Proof of causality can be illustrated through Shepard’s Criteria of Teratogenity “rare exposure-rare defect” approach, meeting the criteria of proven exposure to the agent, careful delineation of clinical cases, and rare environmental exposure with rare defect. Additionally, laboratory findings have discovered several possible mechanisms by which ZIKV can be vertically transmitted, as well as confirming that ZIKV is neurovirulent and disrupts the development of brain structures, especially when infection occurs during the first trimester. ZIKV is also possibly associated with other neurologic disorders: retrospective findings from a 2013 outbreak on French Polynesia linked ZIKV to the neurologic disorder Guillain-Barré syndrome (GBS).
Microcephaly places a significant burden, both emotional and financial, on the affected families and the healthcare system. Therefore, there has been significant effort to develop a vaccine against ZIKV. While ZIKV is a suitable vaccine candidate in some aspects, it also has characteristics that make vaccine development challenging. First, the vaccine must be safe for pregnant women, since protecting them from disease transmission is the primary goal. Second, the vaccine must not cause adverse effects through cross-reacting antibodies, which may lead to antibody-dependent enhancement of infection in people who have been vaccinated against or infected with other flaviviruses, especially DENV. Currently, there are multiple vaccines in the earliest stages of development with three vaccines in Phase 1 trial. Researchers are also testing monoclonal antibodies and antimicrobial drugs for effectiveness against ZIKV. Given the high cost of these treatments they should be prioritized for pregnant women.
ZIKV can be spread through vector transmission, sexual transmission, or blood transfusion. Although vaccine development is the ultimate goal, the most effective way of curtailing ZIKV transmission and reducing incidence of microcephaly is through vector control. Brazil already has vector control strategies in place to combat other mosquito-borne diseases, especially DENV, but its monitoring systems do not always accurately assess mosquito population density and location. There is also an overreliance on insecticide use, which is often ineffective and leads to mosquito resistance and potentially environmental damage. The most effective strategy for vector control is reduction of breeding sites through drainage of standing water, waste management and education about mosquitoes and personal protection measures.
The other key strategy to reducing ZIKV transmission and the incidence of microcephaly is through education about condom use and access to safe abortions. While Brazil has worked to improve the former in the context of the HIV epidemic, with some success, abortions in Brazil are restricted. Data are scarce, but suggests that the number of women seeking abortions has increased due to ZIKV epidemic; limiting abortions leaves them vulnerable to unsafe procedures and at risk for complications that are avoidable.
The ultimate goal for preventing ZIKV-associated congenital microcephaly, and other negative consequences of infection, is the development of a vaccine. However, implementing prevention methods against all mechanisms of ZIKV transmission is the best option to reduce the public health burden until such goal is achieved.
| Identifer | oai:union.ndltd.org:bu.edu/oai:open.bu.edu:2144/23853 |
| Date | 13 July 2017 |
| Creators | Stetson, Alyssa |
| Source Sets | Boston University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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