Climate disruption is expected to change the frequency and severity of infectious diseases. A major avenue for this change will be through one of the most intractable, irritating, and misery-inducing creatures that the world has ever known: The mosquito.
When temperatures rise and humidity hits, mosquitoes – supremely efficient disease vectors – thrive. They love warmth, moisture, and the blood of mammals. Through rising temperatures and increased precipitation, climate disruption will likely alter the range of mosquitoes, which will then carry diseases into new areas.
The zika virus, now sweeping through the Americas, may be a harbinger of this new dynamic. According to Dr. William Reiser, Editor of the Journal of Entomology and Professor Emeritus at UC Davis,
“The warmer it is and wetter it is, the more mosquitoes there are, the faster the population grows, the more often they bite, and the faster they transmit virus.” Zika is just one of many viruses for which this is true, he says, citing dengue, chikungunya, and yellow fever. “This is true of all these viruses,” he says, “not specifically zika.”
The zika virus is a fast-moving situation in which health officials are scrambling to mount an effective response without causing panic. Since I last wrote about the virus, there have been several new developments.
Here’s what you need to know right now.
- Microcephaly is not the only adverse health outcome linked to the virus. There is no definitive link between zika virus and microcephaly, a severe birth defect in which the brain and skull do not fully develop. However, there is strong circumstantial evidence that zika virus infection in pregnant women increases the risk of microcephaly in their babies, and health officials are not waiting for definitive evidence to act. But microcephaly is not the only health problem tentatively linked to the virus, which generally presents with mild symptoms or without symptoms at all. Researchers are also exploring whether zika increases the incidence of Guillain Barre, an autoimmune disorder that causes temporary weakness and paralysis. As the New York Times reported, infection with zika may also be linked to eye and ear problems in babies, even if they do not have microcephaly. In all these cases, the links are not certain, and research is ongoing.
- Testing is not just for pregnant women. The Centers for Disease Control (CDC) has said that some babies should be tested for the virus. The official guidelines state: “Zika virus testing is recommended for 1) infants with microcephaly or intracranial calcifications born to women who traveled to or resided in an area with Zika virus transmission while pregnant; or 2) infants born to mothers with positive or inconclusive test results for Zika virus infection.” The reason for these tests is to screen for and detect the full range of health outcomes from zika virus infection, which may include eye and ear problems as well as the devastating brain defect known as microcephaly (see above).
- The virus does not appear to linger in the body. That’s good news for women who have visited infected countries recently, when not pregnant, but who may want to get pregnant in the near future. If you were infected, you will have immunity from the virus once you recover. And doctors think conception is safe after that. Only 1 in 5 people infected show symptoms, so you may not know if you were infected, but there is no need for testing if you were not pregnant at the time of travel.
- Zika is spreading, and quickly — but not in the continental US. The virus has been detected in 22 countries and territories in the Western Hemisphere – including Puerto Rico and the US Virgin Islands. That notwithstanding, the US is not at high risk of a widespread zika epidemic. According to Dr. Reiser, there is a “minimal likelihood” of zika spreading throughout the US. His rationale? We would have already seen a widespread epidemic of dengue, which is spread by the same mosquitoes. The US is good at interrupting virus transmission, he says, through mosquito control and bite avoidance (otherwise known as window screens and air conditioning). He predicts instead that there’s “a good chance of zika taking off in those scenarios where there have been dengue outbreaks” – such as in Hawaii. So far, 31 Americans have tested positive for zika infection, all contracted while traveling abroad.
- Global health experts are worried. Officials at the World Health Organization (WHO) have warned of an “explosive” spread of the virus in the Americas, and the group is convening an emergency meeting on Monday (Feb 1) to determine the appropriate response. The WHO is weighing whether to declare a global public health emergency – something the agency has been criticized for not doing soon enough in 2014’s Ebola epidemic. Despite zika’s relative mildness compared to Ebola, a coordinated global response may be needed to stave off a wave of devastating birth defects in the Americas.