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In The Country


Tim Iverson

(3/2016) On the cover page of what is largely regarded as the definitive repository to all things knowable is inscribed the phrase "Don’t Panic." Sage words proffered from the fictional Hitchhikers Guide to the Galaxy, but relevant all the same. Currently much of the South American continent is embroiled in a viral epidemic being delivered by a pest making courtesy house calls. While the Zika virus is worthy of our attention and merits serious discussion, reason and verifiable treatment approaches should be the number one concern of public health and governmental officials.

A number of methods are being deployed or being considered to combat the viral epidemic, but should the scientific or world community rally behind all of these options? Vector borne illnesses aren’t just confined to mosquitoes of South America - we have some right in our backyards too. In the United States we may not have the Zika virus, but you can find other vector borne illnesses like Lyme disease, Chagas disease, West Nile Virus, and Hantavirus. Informed response dictates the most successful reduction of infection. Just because we have weapons in the arsenal doesn’t entitle authorities to utilize them all. Reasoned, measured, and scientifically verified approaches will provide the best defense against these and other threats.

Vector borne diseases are diseases that rely on other organisms (like mosquitoes, ticks, mice, etc.) for transmission of the pathogen to other animals. In the case of the Zika virus (or other mosquito borne diseases) only females can transmit the virus, because only female mosquitoes bite humans. They rely on blood to produce eggs. The mosquito feeds on blood and at some point comes into contact with virally infected blood. The virus travels to their gut and through their circulatory system to their salivary glands. Mosquito saliva contains an anticoagulant which is injected into its victims to prevent blood clotting in their proboscis. When the anticoagulant protein is injected into the victim the virus is spread simultaneously. This is how mosquito borne illnesses are spread.

Until recently Zika virus has been relatively unremarkable. It was first discovered in Uganda in 1947. Symptoms develop within a few days of infection and are generally mild. Symptoms include fever, rashes, muscular pain, headache, fatigue, and conjunctivitis. They usually subside in two to seven days. For treatment doctors recommend rest, drinking plenty of fluids, and taking other common medicines for the joint/muscle discomfort. Because the symptoms have historically been so mild and short lived there hasn’t been any great effort to research a vaccine.

Zika is spread by the Aedes aegypti mosquito. This little pest phenom generally feeds during the day, thrives in urban areas, and can lay eggs in an amount of water as small as a bottle cap. The mosquito and virus has been found widely throughout South and parts of Central America, but originally hails from Africa. Only confirmed Zika cases in the United States are from people who have travelled to affected areas. No Zika infected mosquitoes have been found in the continental United States, but this mosquito can be found in parts of the US (even as far north as DC in warm summer months). While not a new virus, concern suddenly arose from statistically significant increases in cases of Guillain-Barré syndrome (an autoimmune nerve disorder) and microcephaly (birth defect). This occurred at the same time as a large increase in ZIka cases. The World Health Organization (WHO) and the Center for Disease Control (CDC) have stressed that there is not a definitive link between the Zika virus and and these health conditions. The WHO state, "Agencies investigating the Zika outbreaks are finding an increasing body of evidence about the link between Zika virus and microcephaly. However, more investigation is needed to better understand the relationship between microcephaly in babies and the Zika virus."

Efforts to combat potential epidemic and further outbreak rely largely on simple, yet effective, prevention methods. WHO and CDC health officials urge the use of long pants/sleeves, insect repellent, staying indoors, use of mosquito netting to reduce risk of exposure, and emptying or draining standing water to prevent reproduction. In many spheres cries for the reintroduction and use of the chemical DDT are growing louder. Proponents for the use of DDT often frame the debate that environmentalists care more about birds than they do people. Ad hominem attacks like that are not only misleading, but are fundamentally wrong on the subject entirely. DDT was widely used in the early 20th century as a pesticide, but was banned in the United States in 1972.

Many other countries followed suit over the following years. There is precedent for limited and restricted use since the ban. The ban was implemented over human, agriculture, and wildlife health concerns - most notably thinning eggshells causing a tremendous loss in bird populations. Even as recently as 2005 CDC tests indicated that chemical residue from DDT was found in almost all human blood samples despite a ban 30 years ago. Using DDT to combat this epidemic just isn’t a reasonable or effective option. A recent Newsweek article summed up the point perfectly, "According to Joe Conlon, a technical adviser to the American Mosquito Control Association and a former entomologist with the U.S. Navy, using DDT to control Zika is a terrible idea. ‘DDT seems like a silver bullet, but it isn’t.’...Conlon says the Latin American countries where Zika is blooming now used DDT heavily in the 1960s to kill off the Aedes aegypti, which also carries diseases like dengue and yellow fever. It worked, but the mosquitoes in the region developed robust resistance to the pesticide, which may still be lingering in the population.

DDT resistance lasts a long time, he says, because the chemical persists in the environment so long. If you spray a wall with DDT today—a method commonly used because mosquitoes are known to rest on walls a moment after having a blood meal—it could still be coated by DDT in 20 years. The mosquito population continues to be bombarded by the chemical, so the resistance shows up in every subsequent mosquito generation. And even if the mosquitoes aren’t already resistant, they will be. It only takes a ‘few generations’ of mosquito to develop resistance, and when an Aedes mosquito’s life span is about 10 days, that’s not long at all. Conlon speculates mosquitoes could develop resistance within a year. ‘What’s even worse, resistance to DDT can stir cross-resistance to the other pesticides we use, like the pesticide we use to treat bed nets, to fight malaria.’"

A more effective approach may be the introduction of genetically modified mosquitoes, and it is currently being evaluated by the WHO. Clinical trials have been conducted in other areas of the globe with success. Essentially sterile males would be introduced into the environment, which would slow the reproduction rates. By watering down the supply of viable mating males reproduction would exponentially slow thus slowing the rate of infection to the human population. Field trials in the Cayman Islands show sharp declines in the mosquito population there, and is promising for potential use in Brazil.

Other methods which are underway in Brazil is genetically altering the DNA to cause mosquitoes to die off before breeding age. Some field tests show up to a 90% decline in mosquito populations. This is a steep decline and they are an invasive species, so this would in essence help to bring back the balance of the natural ecology of the region. It is important to remember that Zika virus is relatively mild and many cases never develop symptoms at all. Additionally, the connection between microcephaly is still unsubstantiated. The Aedes aegypti mosquito is a known transmitter of very serious diseases such as Dengue Fever. The mere potential for birth defects and more serious disease is cause enough to act. As responsible scientists, governments, and people we must not jump to conclusions - rather target our approaches to utilize tools in the toolbox that are known to be empirically safe and effective.

Read other articles by Tim Iverson