Bracing for Zika

For many years, it seemed like new things happened relatively slowly in public health in Texas, where I live. In the early 1990s, entomologists reported the Asian tiger mosquito for the first time — a daytime-flying mosquito from Japan that is not shy about biting humans. Then in 2002, the first cases of West Nile virus (WNV) hit the state. Carried by the southern house mosquito, WNV affected a couple of hundred people or fewer each year. This was the case until the blazing hot summer of 2012 when more than 1,800 cases were reported, including 83 deaths. Health departments throughout the state are still reeling, in some ways, from the impact.

In late 2015, health officials began bracing for another mosquito-borne disease caused by the Zika virus. A cousin of WNV and dengue fever, Zika has been thought of as a less severe form of these flaviviruses. Most people who get Zika show no, or very mild, symptoms. Others exhibit flu-like symptoms including fever, rash, joint pain and conjunctivitis (inflammation of the eye). Most people do not get as sick as with dengue fever or chikungunya, and they recover quickly, usually within a week.

For this reason, since its discovery in 1947 until 2007, it was not on the radar of many public health experts. But in 2007, Zika cases started to spread throughout Micronesia French Polynesia, and eventually Easter Island. There, it was thought to possibly be the cause of a 20-fold increase in cases of Guillain-Barré syndrome — an autoimmune disease of the central nervous system that can be highly disabling, at least temporarily. In 2014-15, the disease made its appearance in Brazil and has since spread to at least nine other member states of the Pan-American Health Organization (PAHO/WHO), prompting that organization to issue an alert to its member public health agencies.

Here’s where things get a little scary. Since the arrival of Zika to Brazil, the virus has been detected in babies born with microcephaly — a relatively rare condition where the brain fails to develop normally. It may result in miscarriage or in babies being born with under-sized brains. It has no cure. The PAHO/WHO alert noted that the number of diagnosed cases of microcephaly in Brazil had increased 10 times — to 2,700 cases — by the end of 2015.

2016 Updates. As recently as December, when Merchant posted his blog (http://insectsinthecity.blogspot.com), it was uncertain whether there was a connection between the unprecedented increase in microcephaly and the arrival of Zika. Public officials “guessed” that the cases may be a result of a pregnant woman being bitten by an infected mosquito.

By February, additional evidence had been gathered to support concerns over the possible connection between Zika and microcephaly. Accordingly, the Centers for Disease Control and Prevention (CDC) issued its highest alert level for the Zika outbreak. The essential facts that CDC is publishing are:

• Zika can be spread from a mother to her fetus during pregnancy.
• The risk of birth defects is sufficiently established that pregnant women are urged to consider postponing travel to areas where Zika virus transmission is ongoing.
• Pregnant travelers returning from infected areas are encouraged to be tested for Zika infection, whether they exhibit symptoms or not.
• Locally acquired cases of mosquito-transmitted Zika have not yet been recorded in the continental U.S., however this could change.
• Zika is spread mostly by the bite of an infected Aedes species mosquito, an aggressive daytime and evening biter in much of the U.S., especially in the south.
• There is evidence that the Zika virus can be sexually transmitted by a man, but it is not known if women can transmit it.

Two Aedes mosquitoes — the yellow fever mosquito (Aedes aegypti) and the Asian tiger mosquito (Aedes albopictus) — are common throughout Texas and the southern United States, and are thought to be the most likely vectors of Zika. Unlike WNV, which is primarily a disease of birds, Zika is solely a disease of primates. To be spread among people, it must be picked up from another infected human. According to one expert quoted in The New York Times, it could be that the risk of microcephaly is increased among people who have previously contracted dengue fever or chikungunya, neither of which are common to Texas or the U.S. If this hypothesis proves correct, the risks to the unborn in this country would likely be negligible.

Dengue and chikungunya are similar, human-only, viruses that have not been quick to spread in the U.S. This may be the result of lower rates of mosquito biting in the U.S., perhaps due to a more indoor lifestyle, or more common use of repellents. Some experts argue that for similar reasons Zika is likely to be slow to establish in the United Statees. Nevertheless, Brazil shows that given the right conditions, this virus is capable of establishing itself rapidly, with 85,000 known infections in its first year of spread. The virus also has been confirmed in several countries of Central and South America, the Caribbean, the Pacific Islands, Cape Verde and Mexico —with CDC Level 2 Travel Alerts for all.

Zika Occurrence in the U.S. As of early February, CDC reported 52 travel-associated Zika virus cases in U.S. states with no locally acquired vector-borne cases reported. However, these cases were widespread — from Florida to Massachusetts and Minnesota to California, with the greatest number occurring in Florida (16) and Texas (10). Additionally, there were nine locally acquired cases and one travel-associated case in the U.S. territories of Puerto Rico and the U.S. Virgin Islands.

Because of this, on Jan. 22, 2016, CDC activated its Emergency Operations Center (EOC) to respond to outbreaks of Zika occurring in the Americas and increased reports of birth defects and Guillain-Barré syndrome in areas affected by Zika. Then, on Feb. 8, 2016, CDC elevated its EOC activation to a Level 1, the highest level.

Although Zika has not yet been seen to be locally transmitted in the continental United States, the mosquitoes that can carry Zika are found in some areas of the U.S. Additionally, because the mosquitoes that spread Zika virus are found throughout the tropics, outbreaks will likely continue. And, as written by Merchant in December, there still is no vaccine or medicine for Zika.

As Merchant also noted, “Be prepared to hear more about the Zika virus this year. It may turn out to be a big event, or it may not.” It has, which makes his closing statement that much more critical, “Even if we didn’t need more reasons to dislike biting mosquitoes, now we have one more reminder of the importance of residential mosquito control, and putting on the insect repellent when venturing outdoors.”