Zika Virus At Our Doorstep

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A female Aedes aegypti mosquito takes a blood meal. Photo courtesy of James Ganthany.

In our global village, what happens in the remote areas of distant continents often makes its way to our back door. The little known virus, Zika, has spread like wildfire through the Americas, so naturally here in Texas we worry about it heading our way. We have the mosquito vector and a susceptible human population, but will we have Zika?

It's a definite possibility.

The Zika virus has been known to exist in Africa and some parts of Southeast Asia since the early 1950s. The University of Texas at Galveston, Medical Branch’s World Reference Center for Emerging Viruses and Arboviruses maintains stocks of Zika and many other little known viruses. We never know which virus will pop up seemingly out of nowhere.  But Zika typically causes a very mild, flu-like illness, so it wasn’t considered an important human disease.

That all changed in 2007 when Yap Island, a small chain of islands in the Federated States of Micronesia, suddenly had an outbreak of Zika, which had never existed there before. Zika crossed the Pacific to an island popular with western tourists for its renowned scuba diving.

It took more than 50 years for it to move out of Africa and Southeast Asia, but only eight years for it to start island hopping across the Pacific. In 2013, an outbreak occurred in French Polynesia.

How long until the virus spread further? Not long, it turns out.

By May 2015, it had arrived in Brazil, where an outbreak was in full swing. In the past six months, Zika has rapidly spread throughout much of Latin America.  The otherwise mild illness would likely have gone unremarked, had it not been for an increase in cases of babies born with a smaller than typical head, or microcephaly. In a country that usually has less than 150 cases of microcephaly per year, Brazilian authorities reported more than 2,500 cases in October 2015.

An educational alert from the Centers for Disease Control.

A number of the pregnant mothers had been infected with Zika during their pregnancy. Suddenly, this "unimportant virus" became a very real threat.

While correlation does not equal causation, evidence is mounting, as this week the Centers for Disease Control confirmed that Zika virus was found in the amniotic fluid of two babies diagnosed with microcephaly in utero.  Brazilian authorities are also reporting an increase in Guillain-Barré (GB) syndrome, a very rare disease that can cause muscle weakness and paralysis. Whether these cases are due to Zika infection or coincidental remains to be determined.

What's most frightening is how quickly the virus has spread.  The World Health Organization (WHO) has convened an emergency meeting to review the situation, something they were slow to do in the early days of the recent Ebola outbreak. Eyeing our long shared border with Mexico, Texans are wondering how long before we see cases of Zika virus here.

U.S. Distribution of the Zika vector, Aedes aegypti

Transmitted to humans by the mosquito vector, Aedes aegypti, it could spread wherever the mosquito lives, provided it has susceptible humans to infect.

The mosquito is already firmly established in parts of Texas. It's an urban mosquito that thrives near large populations and bites during the day time hours.  Its close relative, Aedes albopictus or the “Asian Tiger Mosquito,” is common in San Antonio. A black mosquito with white spots, it is easy to spot when it’s biting you.

How do we stop the virus from coming here, and what do we do if it does?

A vaccine for Zika is likely to be years away, so while scientists led by Dr. Scott Weaver, Director of the Institute for Human Infections and Immunity at UTMB, continue to study the virus, other teams are attacking the mosquito. One method is to sterilize males and release these into the population. This tactic worked to eradicate screwworm from Texas years ago.   The sterile male mosquito, who doesn’t bite, mates with a female but the female cannot produce viable eggs. Fewer mosquitoes means less likelihood of disease (and fewer bites), but this method requires continual release of male mosquitoes over time to reduce the population, is costly and challenging to maintain over such a large area.

A second option is to block the infection in the mosquito.  This is done by using a harmless bacterium, Wolbachia, which already lives in the mosquito. Dr. Steven Sinkins, Professor of Biomedicine and Wellcome Trust Senior Research Fellow at Lancaster University in the UK has developed Wolbachia-infected mosquitoes that block dengue and chikungunya viruses and are very likely to stop infection with Zika as well. “Wolbachia replacement to make the vectors unable to transmit would be a much more stable and efficient control strategy long-term,” said Dr. Sinkins, as he prepared to travel to French Polynesia where the current Latin American strain originated.

The most important thing we in San Antonio can do to prevent Zika is to remove mosquito breeding sites: empty any container where water pools. Aedes mosquito eggs can live a very long time with no water and emerge soon after a rain, so clean out the containers to remove any eggs.

Typical breeding site for Aedes aegypti mosquitoes in St. Croix, USVI, during a chikungunya outbreak. Photo courtesy of CDC

Typical breeding site for Aedes aegypti mosquitoes in St. Croix, USVI, during a chikungunya outbreak. Photo courtesy of CDC

Given the distribution of the mosquito, it's not a stretch for Zika virus to gain a foothold in South Texas. That Zika is a mild disease may also cause the greatest risk. A slight fever in a returning traveller is likely to go undiagnosed, which means more people infected before public health officials become aware of it. More infected people means a greater chance the mosquitoes will pick it up. All the more reason to see your health care provider if you recently returned from travel abroad and have even mild flu-like symptoms.

San Antonio Metro Health District is educating the public and health care providers to be alert to symptoms, particularly in individuals who have recently returned from an infected area. Typically, a virus needs more than one infected person to take off in a population, but if multiple infected people go undetected, the outbreak potential is there.

Our ability to travel across the world in a matter of hours means that we can no longer ignore public health threats in far off places. Diseases in Central Africa, Southeast Asia, or Latin America are on our doorstep. Only continued surveillance and scientific research will stop, or at least slow their spread. We never know what the next disease lurking will be.

*Top Image: A female Aedes aegypti mosquito takes a blood meal. Photo courtesy of James Ganthany.

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