Long-Term Approach Is Necessary
So, why would the WHO make such a move? Well, it is primarily because Zika virus will require a long-term strategy rather than an emergency response to combat it. But just because an emergency response won’t contain the virus from continuing to spread, individuals can still take important precautions to limit their potential exposure to it.
Zika virus is unlike other mosquito-borne viruses (e.g., West Nile, yellow fever, chikungunya, and dengue viruses) infecting humans. Zika virus can also be spread through sexual transmission. And, although 80 percent of Zika virus infections are asymptomatic, infection with the virus can lead to birth defects in utero and an autoimmune-linked neurological disorder, Guillain-Barré syndrome (GBS), in adults as well.
Aedes aegypti mosquitoes carry many viruses associated with human disease, including yellow fever, dengue, chikungunya, and Zika viruses. A. aegypti can actually carry more than one of these viruses at a time.5 This is leading some doctors and researchers to hypothesize that coinfection or sequential infection with Zika and dengue viruses or Zika and chikungunya viruses may be contributing to the increased incidence of microcephaly (and GBS) in Brazil, where all three viruses are concurrently circulating in the mosquito population.
Much of what predisposes some human beings to disease upon infection is still poorly understood, but factors in Zika virus–associated disease may include coinfection with other viruses such as dengue and chikungunya. Prior infection with dengue or chikungunya could also leave people more susceptible to disease upon subsequent infection with Zika virus. Observations indicating coinfection and sequential infections as possible triggers of disease have been made, but correlation is not causation, and further studies need to be done to determine the exact elements contributing to disease.
The United States Allocates Funds for Combating and Researching Zika Virus
Numbers of cases of Zika virus infection continue to grow in the United States and US territories. In September, Congress passed a bill allocating $1.1 billion for Zika virus public health and research initiatives. In addition to implementing public health measures and continuing studies to determine correlates of disease, two candidate vaccines have been approved for clinical trial. One is based on DNA and the other on a killed virus vaccine.6 But until the correlates of disease and immunity are identified, availability of a Zika vaccine before 2018 is unlikely. By then Zika virus will have likely spread throughout the United States (and globally) to much higher than current levels.
Status of Zika Virus Infections in the United States
Zika virus disease and congenital infection are nationally notifiable conditions. The CDC statistics for the United States as of November 30, 2016, show widespread, locally acquired infections in Puerto Rico. Additionally, all 50 states have had a least one case of imported Zika virus. Almost all locally acquired cases (184 of 185 as of December 7, 2016) are currently limited to a single area of South Miami Beach, Florida (Miami-Dade County). One locally acquired case has been confirmed in Brownsville, Texas, during the week of November 23, making Texas the second state with local transmission.7 Travel warnings are in effect, and pregnant women are especially cautioned against travel to these areas.