As the world continues to warm, we’re starting to see a host of previously neglected tropical diseases right here in the U.S. Although climate change alone is not solely responsible -- increasing income inequality, for example, has led to greater numbers of Americans living in poverty and the accompanying substandard housing and poor sanitation create fertile ground for these diseases to take hold -- it’s a major contributor to the problem.
The key vectors of these diseases are aggressive insects like mosquitoes that are being drawn northward by increasing temperatures. They carry the pathogens that cause diseases such as Chagas disease, dengue fever, chikungunya fever and the Zika virus -- exotic tropical diseases that previously you may have only read about in news reports.
Most tropical diseases usually aren’t spread person to person but require insects to bite an infected host and spread the infection to another person, with a notable exception for Zika: Mothers can pass the virus to their unborn children during pregnancy or around the time of birth, according to the Centers for Disease Control (CDC).
1. The Zika Virus
A mosquito-borne virus, the Zika virus arrived in the Western Hemisphere in Brazil, with the first reported case in May 2015. The symptoms are very much like dengue fever -- fever, rash, joint pain and conjunctivitis -- without the more serious complications. Most adults, in fact, remain asymptomatic and never know they've been infected. However, Zika has now been associated with serious brain damage in the unborn babies of infected mothers, with more than 3,000 cases reported in Brazil in 2015 alone.
The CDC has issued a travel advisory recommending that pregnant women or women contemplating pregnancy not travel to most of Central and South America and much of the Caribbean. Pregnant women who have traveled to those areas should contact their obstetricians for further guidance. Screening protocols and advisories are being created and revised almost daily, so check CDC.gov for the latest news. At present, there's no vaccine or treatment for the Zika virus.
*UPDATE _(as of February 2)__: Texas health officials report that a case of sexually transmitted Zika has been confirmed by the CDC in Dallas County. Zika infections have been reported in the U.S. in Americans who have returned from Central and South American countries in which Zika outbreaks have occurred. A CDC health advisory states that these imported cases of Zika "may result in human-to-mosquito-to-human spread of the virus."_
2. Chagas Disease
Chagas affects millions of people in Central and South America and at least 300,000 people in the U.S. are infected by Trypanosoma cruzi, the parasite that causes the disease. It’s transmitted by insects that resemble bedbugs and that are often referred to as "kissing bugs" because of their predilection for biting victims on the face. After they bite, the insects defecate on the skin and the parasites which reside in the insects’ stool then enter your body through your mucus membranes or cracks in your skin. Simply scratching the itchy bites is often enough to create tiny breaks in the skin that can serve as an entry point.
Initial symptoms mimic the flu and include fever, muscle aches, headache, fatigue and gastrointestinal upset. If you see a doctor at this stage, the diagnosis will almost always be missed unless you have one of the uncommon telltale signs of the disease: swelling of the eyelid on the same side of the face as the bite or a local swelling at the site of the bite.
After the acute illness resolves, the disease enters a quiescent phase. But over ensuing years, patients can develop life-threatening heart or intestinal disease; in Brazil, Chagas is one of the leading reasons for heart transplantation. Most cases in the U.S. are picked up while traveling abroad, but as the kissing bugs migrate north, we’re seeing more and more cases in people without a travel history. In Texas, 1 in 6,500 screened blood donors now test positive for T. cruzi. Treatment is available, but is most effective only early in the disease.
3. Dengue Fever
Dengue fever is mosquito-borne and is caused by several related viruses. Almost 400 million people are infected every year worldwide. It, too, has arrived in the southern U.S. and has long been a problem in Puerto Rico. It usually presents with fever, severe headache and eye pain, joint, bone and muscle aches, rash and mild bleeding from the nose and gums. Severe low-back pain is very common and has given this disease its nickname, “breakbone fever.”
In most patients the fever eventually goes away, but it can also progress to what is called dengue hemorrhagic fever, with severe abdominal pain, shortness of breath and bleeding from blood vessels throughout the body leading to shock and potentially death. Although there is no specific therapy to treat the virus, aggressive support in a hospital setting can keep mortality rates very low.
4. Chikungunya Fever
This fever is also caused by a virus carried by mosquitoes. It originated in Africa and has spread throughout the world, with millions of cases reported. The first cases close to home were reported in the Caribbean late in 2013, and by the end of 2014, more than 650,000 cases had been identified in the Western hemisphere. Most cases in the U.S. are in returning travelers, but local transmission has also occurred. It can appear very much like dengue fever with high temperatures, rash, headache, muscle aches and particularly profound joint pains. Most people get better in a few days, but some continue to have symptoms for many months. And like dengue, there’s no definitive cure.
Should you be worried about these -- and other -- tropical diseases that are finding a home in the U.S.? Worry alone never solved anything, but proper concern combined with the knowledge that allows us to recognize these illnesses and get proper treatment can make a difference. Right now, prevention is probably the medicine. TIPS: Reduce your exposure to bug bites by wearing long-sleeved shirts and long pants when outside, use insect repellents and take steps to prevent insect infestations in and around your home. And finally, be vigilant when traveling to areas where these diseases are endemic.
Malcolm Thaler, M.D., is a physician at One Medical Group. He is the author and chief editor of several best-selling medical textbooks and online resources and has extensive expertise in managing a wide range of issues, including the prevention and treatment of cardiovascular disease, diabetes and sports injuries.
Thaler graduated magna cum laude from Amherst College, received his M.D. from Duke University and completed his residency in internal medicine at Harvard’s New England Deaconess Hospital and Temple University Hospital.