Could climate change be the culprit in spread of Zika virus?
The Zika virus sweeping across South America may be only one of several long-dormant infections that will resurface in coming years because of climate change and deforestation, says a Johns Hopkins University neurologist now leading research efforts in Colombia, one of the countries hardest hit by the disease.
According to Dr. Carlos Pardo Villamizar, warmer climates may have triggered the emergence and subsequent spread of the Zika virus by making more of the world habitable for the Aedes aegypti mosquito, its main carrier. Higher temperatures and dryness have been linked to the spread of another mosquito-borne illness, dengue, and deforestation is thought to be a cause of the most recent Ebola outbreak in Africa.
The neurologist suspects that Zika, which so far has struck 42,000 Colombians, may also have caused other complications, including a 50% increase in Guillain-Barre, a nervous system disorder causing partial paralysis. There have been no reported cases in Colombia of newborns with microcephaly, or abnormally small heads, as seen in Brazil. But Colombia’s more than 6,600 Zika-infected pregnant women are being monitored.
The Zika epidemic – why now?
Although Zika was discovered in the 1940s, it remained dormant for many decades, reappearing in Micronesia about 10 years ago. Since then it has slowly spread to other areas of the world. But no one paid any attention to it until now because there was no epidemiological problem, no great outbreak of the virus. “Why now?” is a matter of ecology and environment.
The magnitude of the problem we are seeing in South America will not be seen in the United States because the mosquito cannot live in the majority of the U.S. Parts of the South could be vulnerable, but the ecology of most of the U.S. is not conducive to the presence of the Aedes aegypti mosquito, which is the main vector, or carrier, of Zika.
What makes the disease so threatening?
The mother’s exposure to the virus in the early stages of pregnancy could lead to microcephaly in a small subset of patients. But the fetus is potentially vulnerable to neurological complications at any stage of pregnancy. It’s very possible that viral infections in later stages of pregnancy could lead to future developmental disorders for the child in the future, such as epilepsy and learning and language disabilities. The spectrum of neurological problems that could emerge is quite wide.
What makes the Zika virus so potentially harmful to newborns?
In a subset of victims, Zika triggers a change in their immune systems. It seems to produce a kind of cross-attack against the nervous system. We suspect the virus may have the direct capability to attack the brain and spinal cord. Scientists in the 1950s experimenting with animals were able to demonstrate that Zika targeted neurons, the cellular elements of the brain and spinal cord.
You say that Zika’s apparent role in promoting Guillain-Barre disease is as worrisome, if not more so, than microcephaly. Why?
I have just come from seeing a Guillain-Barre patient here in Cali and it is horrible to see how they are left weak and incapacitated. It can be devastating for them and for caregivers. It is a temporary condition in most cases, but it is very aggressive and some will be incapacitated for the rest of their lives. Patients can be left with a lot of consequences, such as atrophy of muscles and a deficit in sensations. You talk to neurologists in affected areas who before may have seen three or four cases a year who now are seeing 10 or 15 per month. That’s the magnitude of the problem. In Brazil the increase in Guillain-Barre cases since the Zika outbreak is even more striking.
We know that dengue follows a pattern of climate change and that dengue and Zika have a common vector or carrier, the Aedes mosquito. It’s well known in South America that when you have El Niño climate conditions of dryness and heat, dengue cases increase. And where there is dengue, you have the possibility of Zika.
What treatment is there for Zika, and is there hope for a vaccine?
There is no treatment and a vaccine will take years and years to develop. You need to first find a vaccine, then test it for safety and efficacy. How much money and how many years have we spent looking for vaccines for malaria and dengue? So it is very challenging. A better approach in the near term is to control the spread of the mosquito.
You can easily imagine a doomsday scenario for Zika.
We are still learning about the disease, but there are biological features which make it different from dengue and chikungunya. There is evidence that Zika is present in the urine, saliva and semen. That means the virus has the potential to attack different cell populations and organs, whereas dengue affects mainly the blood. That means Zika has a potential to cause more complications from the disease and for it to spread.
Looking ahead, what encourages you?
In January we established a task force of researchers from Johns Hopkins and Columbia University medical schools and the National Institutes of Health with our Colombian colleagues at six different university hospitals here. Many fields of expertise are represented, such as neurology, virology and maternal-fetal medicine. Collaboration is the only way to learn about this disease, not just to diagnose the neurological problems but the factors behind this emerging disease, in order to design treatment and ways of managing patients.
But we need support. We have been knocking at the door for federal grants but nothing has come through. I’m here thanks only to philanthropy from a family foundation called the Bart McLean Fund for Neuroimmunology Research, which has been supporting Johns Hopkins for 10 years. I asked them if I could divert some of their support to Colombia and the family quickly agreed.
Kraul is a special correspondent.
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