How to Fight Zika — Lessons from the Panama Canal

By Mark A. Kelley, MD |08/08/16

The Zika virus continues to capture headlines. Zika virus has been found in Puerto Rico and now in a Miami Florida neighborhood.

Is this the beginning of a major epidemic? Not likely – if we follow the lessons of the Panama Canal.

I recently visited Panama and its famous canal that links the Atlantic and Pacific Oceans. The canal was built between 1880 and 1914 at the cost of many lives. Over 30,000 workers perished, most of them dying from tropical diseases. The most deadly were malaria and yellow fever. The latter could kill some victims within a week.

The tropical disease epidemic in Panama was stopped without the use of any vaccines or drugs. The key was understanding how mosquitoes spread these diseases to humans. Female mosquitoes need blood nourishment to lay their eggs. Infected mosquitoes can transmit the diseases to humans when they sample human blood. Eliminating mosquitoes prevents the disease.

Zika virus, known for almost seventy years, belongs to a group of tropical viruses transmitted by mosquitoes. Among them are yellow fever and dengue fever.
Until recently Zika was not considered a major public health problem because it rarely caused problems in humans.

Now Zika has changed and become dangerous. When the virus is transmitted from an infected woman to her fetus, the infant may be born with major birth defects, particularly of the brain. At the moment we have no drugs or vaccines to fight Zika.

This sounds like the Panama problem in the early 1900s. What stopped the epidemic back then?

The answer came from understanding the aegypti mosquito, the major carrier of these viruses. Each mosquito lives only 2-4 weeks. The female lays hundreds of eggs that hatch immediately upon contact with water. In dry conditions, these eggs can survive for 12 months. The resulting larvae emerge as adult mosquitoes in about ten days.

Aegypti mosquitoes have several important characteristics.

1. They stay close to human dwellings and need very little water for their eggs. These bugs prefer to be close to their victims and hide in and near dwellings –not in the jungle. They love stagnant water to lay their eggs. Human dwellings, with flowerpots and gardens, sinks and toilets, are perfect. During the Panama Canal construction, mosquitoes were happily breeding in the inkwell of the chief physician!

2. The typical female travels no more than a quarter mile during its lifetime. The only way for Zika virus to leave the neighborhood is by “hitching a ride” with a human. In the Miami outbreak, the “neighborhood” where Zika was found is about 10 blocks wide and 20 blocks long. An infected human who leaves this “Zika zone” may bitten by a mosquito in a new location that is “Zika-free”. If that local mosquito becomes infected, it can pass Zika to victims in the new neighborhood.

3. They like to bite humans during the day. This makes prevention more challenging for those who leave their home during daytime.

What stopped the Panama Canal epidemic a century ago? Public officials declared war on these mosquitoes with an aggressive action plan:

• Every house and neighborhood was inspected regularly to eliminate standing water and stop mosquitoes from breeding. All water containers were cleaned weekly to kill any eggs or larvae.

• Irrigation ditches and swampy areas near homes were drained.

• To prevent spread, yellow fever patients were kept in isolation from mosquitoes.

• Workers and the general public covered up with long sleeves and pants to reduce the chance of mosquito bites.

The plan worked. In less than one year, the yellow fever epidemic ended. .

Today, we have many more tools to fight this virus – window screens, air conditioning, municipal sanitation, and effective insect repellant. Also many regions in the U.S. either are too dry or too cool for the aegypti mosquito to thrive.

We still have much to learn about Zika. One surprise is that Zika can be transmitted by sexual contact. This makes things more complicated and prevention recommendations are still evolving. Hopefully, a Zika vaccine may eventually emerge, as happened with yellow fever.

Meanwhile, the lessons of the Panama Canal still hold true:

• Eliminate standing water near humans.

• Prevent mosquito bites by staying inside screened dwellings. When outside, wear clothing that covers the skin and use insect repellent.

These measures are effective. During a five-day visit to Panama City, none of my family and friends was bitten by a mosquito. In fact we never saw one.

For the most accurate and up-to-date information about Zika, check the Centers for Disease Control website. There you will find details about prevention, transmission, and Zika in Florida and other locations.

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