The week before Thanksgiving, the World Health Organization (WHO) ended the international public health emergency status for the Zika virus that was enacted on February 1, 2016. So why isn’t that just one more thing to be thankful for? It is because the end of its emergency status is not the end of the public health threat nor a demotion of the importance of the Zika virus to public health.
In fact, this past month, one senior federal official at a special Zika press briefing organized by the American Society of Tropical Medicine and Hygiene called the Zika outbreak in the Americas “the most complicated health emergency” the US Centers for Disease Control and Prevention (CDC) has ever handled.1
The change in emergency status is also somewhat surprising, since the WHO reiterated the global health emergency status in early September.2 Furthermore, Zika virus continues to spread through the United States and US territories and throughout South America, the Pacific, and Southeast Asia, where it is currently spreading quickly through the densely packed population of Singapore.3
We have never had a mosquito-borne virus that can cause birth defects. . . . We have never had a mosquito-borne virus that can be spread sexually. We don’t have a great track record with controlling Aedes aegypti. . . . And we have an unprecedented frequency of people traveling to every part of the world and back.4
–Anne Schuchat, MD, CDC principal deputy director
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.
Although we are aware of many viruses out in the world today because of the diseases they cause, we are surrounded by millions of viruses that will never cause disease in humans. By far, the vast majority of viruses help keep bacterial populations in check and contribute to our well-being. Although we can be thankful for the role viruses play in balancing the ecosystem for human flourishing, we should also take precautions and limit travel to highly infected areas and our exposure to mosquitoes in these areas. Human travel to infected areas and back to uninfected areas is contributing more to the spread of Zika virus than any other factor.
Another way of potentially curbing transmission of Zika virus in areas where it is already established and yet to be established is to control the mosquito population. Cuba implemented basic mosquito control measures at a national level and curtailed the spread of Zika virus by local transmission for months, relative to the areas around Cuba.8 Mosquito control efforts have reduced the area of local transmission in Florida’s Miami-Dade County as well.9
Elsewhere, the British company Oxitec has joined the fight against mosquito-borne diseases at a high-tech level. A nonbinding referendum about release and use of Oxitec’s genetically modified mosquitoes was even on Florida voters’ ballots in November’s election. Residents of Monroe County in the Florida Keys passed the referendum, but a specific release site is still to be determined. A 22-month release study has FDA and now voter approval. For more on Oxitec’s modified mosquitoes, click here. To listen to an interview I had on this topic on Live from Seattle, click here.
In addition to genetically modified mosquitoes, bacteria may help control the spread of mosquito-borne viral disease like Zika virus. In two major cities of Brazil and Colombia, an $18 million scale-up to release mosquitoes that carry Wolbachia bacteria in the fight against Zika virus is underway. Once Wolbachia-infected mosquitoes are released, the bacteria spread naturally in the wild mosquito population and render infected mosquitoes resistant to virus infection. Wolbachia is already widespread among insects and does not infect humans. So if this project is successful, it may be a lifesaver in the fight against dengue, Zika, and chikungunya viruses worldwide.10
Much to Be Thankful For
In the fight against Zika, there is much to be thankful for. But an end to the emergency status seems a little premature to me. Calling something a public health emergency keeps it in the forefront of our community consciousness and can help us respond in more thoughtful, responsible, and diligent ways. If we let a false sense of security accompany the change in status, we may take unnecessary risks that could make the public health impact of Zika virus worse than need be.
Join me in praying for wisdom for those making decisions and taking actions that affect the management of resources and the control of the spread of Zika virus disease here and abroad, and in praying for those who suffer from the spread of the virus so far.
To keep up to date on Zika virus in the United States, go to www.cdc.gov/zika.
