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Unsuspecting U.S. Travelers Bring Novel Disease Home, And It Spreads

When a disease threat looms, you might expect that everyday people won’t recognize the danger, but professionals will. That isn’t always the case, though. Some data made public last week demonstrates that even people well-informed about risks can be vulnerable—and underlines the threat that one new disease poses to the United States.

Last week was the annual conference of the Epidemic Intelligence Service of the US Centers for Disease Control and Prevention, the ferocious young disease detectives who are the CDC’s SWAT team for outbreak response. (Don’t they sound intriguing? Look, here’s a book about them.) At the conference, EIS officer Dr. Alex Millman described what happened when a US volunteer organization sent its members to work in the Dominican Republic for stints of 4 to 8 weeks. The Dominican Republic is a hot spot for diseases carried by insects, and so the volunteers and staff attended health briefings ahead of time and talked to their own doctors. During their assignments, 96 percent of 102 whom Millman interviewed wore insect repellent and slept under a bed net. And yet, after they returned, almost half of them, 46 percent, were diagnosed with chikungunya.

If you haven’t heard of chikungunya yet, don’t worry: You will.

Chikungunya is a mosquito-borne disease that causes fever and crippling joint pain that can be long-lasting. There is no vaccine against it, and no specific treatment, other than rest and pain-killers.  It has a long history in  Asia, but is a new arrival in this hemisphere: It was first detected late in 2013, and spread through the Caribbean and Latin and South America with explosive speed. There have now been more than 1.4 million cases, according to the Pan American Health Organization, and as the disease-tracking group CIDRAP noted on Monday, the count is increasing by thousands more each week.

And some of those are in the US. Travelers returning home have brought chikungunya with them: There have been 93 lab-confirmed cases in 24 states so far this year, according to the CDC, and there were 2,481 cases last year, in every state except for Alaska, North Dakota and Wyoming.

map courtesy CDC.gov; riginal here.
map from CDC.gov; original here.

Those cases are important, not just for the suffering of those individuals, but because they pose a threat to people who have not traveled. Sooner or later, someone arrives back in the US at a point in their disease where virus in their blood can be picked up by a local mosquito, risking the start of a chain of infection here—a place where most doctors are still unfamiliar with the disease. That’s not idle speculation. First, the mosquitoes that carry chikungunya range widely across the southern US—and, with warming temperatures, are moving north.

maps courtesy of CDC.gov; originals here.
maps from CDC.gov; originals here.

And, second, this has already happened once: Last year, 11 people in Florida came down with chikungunya without having left the state.

This is the same pattern that led to the reintroduction of dengue in the US (which I covered for Slate in 2012): outbreaks in the Caribbean and South America, and then travel-associated outbreaks in the US in places with the right mosquito species, and then re-establishment of the disease within US borders.

Unfortunately, there is no easy fix. But for their own sake and their neighbors’, travelers can do their best not to be a vector. As the volunteers’ experience shows, though, that is more difficult than it seems: They took the recommended precautions and almost half of them still became infected. The one gap in their armor, detected in Millman’s survey, was that few of them slept in rooms where windows and doors had screens. That demonstrates that it can takes layers of protection to prevent mosquito bites—in some cases, literally layers: the CDC recommends long pants and long sleeves to keep the bugs away.

Except: People don’t go on Caribbean vacations, or even work or volunteer trips, with the expectation that they will be wearing muffling clothing and staying indoors; they go to loll on the beach, hang out in hammocks, and wear as little as possible for as long as they can. Those are reasonable expectations, going to the tropics. It’s possible that coming home with an illness is now a reasonable expectation as well.

15 thoughts on “Unsuspecting U.S. Travelers Bring Novel Disease Home, And It Spreads

  1. Just had a friend develop Cryptosporidium; he has having a difficult time. That is not an easy disease to deal with or treat.

    As a veterinarian in Texas, we hear warnings frequently about incoming foreign diseases. Right now, Chagas is about 30 miles south of my home, Waco, and it is effecting dogs. It is seen further south in humans; in the past, Chagas was never a problem here in my lifetime at least.

    We live in a global society now, so anything can come here in 24 hours or less; that is how we ended up with Ebola in Dallas, a disease no one here had ever encountered.

    MM: Thanks for the comments, especially welcome as I’m a former Texan too (parents lived there from when I was in high school). I am obsessed with Chagas and think it’s an under-appreciated threat — particularly in transplants.

  2. P.S.

    Also, thanks for the article on Chikungunya; that’s a new one on me. I am posting this on our Texas discussion group, 1,000 veterinarians in Texas mostly, and Veterinary Information Network, 50,000 veterinarians worldwide. It may not effect animals, but we need to know what is out there.

    1. >>>>I am obsessed with Chagas and think it’s an under-appreciated threat — particularly in transplants.<<<<

      You are right about that. Anything that can damage your heart like Chagas can scares me. We have the kissing bugs all over our area of Texas; many carry the Trypanasome, but the species we have always had has different feeding and bathroom habits than the primary carrier for humans. Now, we are getting both species, so Chagas is going to become more of a problem for many here and possibly across a larger area of Texas.

  3. Few countries outside the US use window screens, but plastic screens are easy to roll up and pack in a suitcase, and can be tacked or taped up on a window of any size. A mosquito net doesn’t keep bugs from whining in your ear all night, or prevent bites through a net draped on top of your arm while you sleep.

  4. Help stop spread of mosquito borne diseases: download Android app called TrashWatch and report mosquito breeding sites. NO larvae = no mosquitoes= no chikungunya or dengue or malaria…

  5. as a department of defense provider my views are my own and not the official opinion of the DoD, etc. etc.

    I’ve seen time and again that no amount of permethrin-infused clothing, training, and DEET can change the behaviors (especially of young adults) 100%. The layers of protection didn’t fail. the layers weren’t used. I never saw a case of malaria where the 20 something kid used it more often than not. most of them could tell me where it likely happened.

    smoking outside at dusk after dinner is a huge risk in this population. if you really want to lower the risk then the volunteers need to place a deposit and upon return submit to NGO medical screening for 1-4 weeks to include blood draws depending on the risk of the area. if they complete then they get their deposit back.

    MM: Thanks very much for the insight!

  6. Yes, smallpox and other diseases were brought to the American Indians by European colonists. But didn’t syphilis (lues) reach Europe from the New World after Columbus’s voyages? Diseases are no respecter of boundaries, that’s for sure!

  7. I contracted Chikungunya in Samoa in January 2015. Slowly improving but still suffering aching joints and arthritic hips and knees. Take all the precautions in the tropics, trust me: You do NOT want to get this one. I had Dengue and it was a walk in the park compared to this. See my twitter for tips on natural remedies. @CHIKVremedies

  8. mosquitos they can give you diseases so we should have trucks field of mosquito repellent come out and spray more often so your less likely to get a disease it will help alot

  9. Interesting experiment, and very concerning as regards travel to affected areas. Surprising to me, however, was the emphasis on window screens and sleeping under mosquito netting. My understanding (admittedly, as a layman) is that mosquitoes that carry chikungunya virus bite mainly during the daytime. (see, e.g., http://travel.gc.ca/travelling/health-safety/diseases/chikungunya). In that case, preventive measures while awake (DEET, avoiding damp, mosquito-ridden areas, etc.) would seem to be of greater importance than screens and netting in bedrooms. I would be interested in how the experts would respond to my question.

    On a related but different note, I have been surprised at how low-information many travelers are on this topic. I spoke with two different friends who traveled in the Caribbean this past winter and neither had ever heard of chikungunya. I think greater public health information for the traveling public (possibly involving the airlines and cruise ships) is very important, even if no preventive measures will render chikungunya 100% preventable. Meantime, let’s hope for progress in (1) mosquito eradication in affected areas, and (2) progress towards a vaccine.

  10. >>>>mosquitos they can give you diseases so we should have trucks field of mosquito repellent come out and spray more often so your less likely to get a disease it will help alot<<<<

    Spraying really isn't that effective in my opinion.

    With animals and their external parasites, you can spray insecticides only so often. They work for a short time and are gone. The spray insecticides give only very short term results, and not that much actual protection. Here in Texas, late evening spraying to help prevent West Nile is/was only minimally effective in my opinion for any animal, humans, horses, birds.

    Spraying is always called for but when checking the results, the results are often minimal at best. The coverage area is minuscule, the effect short, and the success for dollar invested usually not worth the time and effort. If you are going to slow or halt these diseases, you have to do it in another way; spraying just isn't that efficient.

  11. This is a summer reminder from the Texas Veterinary Medical Diagnostic Laboratory that came in this morning. They are reminding us Chagas is a problem here and to watch and diagnose. More cases are occuring; it isn’t common yet but I believe it soon will be, and the same reduvid bug (several species of course) can infect both humans and pets.

    Since you are interested in Chagas, I thought the message might interest you. Don’t know where you live, but in Texas, Chagas is either already all around us, or on our door step and ready to come in.
    Summer Chagas Surge: Are you ready?

    During the summer months, TVMDL (Texas Veterinary Medical Diagnostic Laboratory) routinely sees an increase in positive tests for canine trypanosomiasis or Chagas disease. Chagas disease is caused by the parasite Trypanosoma cruzi, a hemoflagellate protozoan.

    The blood-sucking reduvid bug, a.k.a the “kissing bug”, transmits the parasite. The vector and domestic and wild mammalian hosts are widely distributed throughout the southern United States, Central and South America. The kissing bug becomes infected when it takes a blood meal from an infected host. Transmission occurs when the infected bug defecates on or near the host during or shortly after a feeding and the infected fecal material is rubbed into the bite wound, skin abrasions or mucous membranes. Oral ingestion of an infected bug is also a probable route of infection in dogs.

    Fatal cases of canine Chagas disease typically occur in young dogs, most often less than one year old. Practitioners and animal owners should be watchful for clinical signs of the disease, especially in young dogs. The phases of the disease can be identified as:

    ACUTE – Signs include fever, anorexia, lethargy, swollen lymph nodes, enlarged liver or an enlarged spleen, and sudden death.

    LATENT – This phase is asymptomatic with the primary clinical sign being sudden death.

    CHRONIC – Congestive heart failure is the most common clinical sign, usually beginning with right- sided heart failure. This may develop into dilated cardiomyopathy and arrhythmias. Progressive lethargy and exercise intolerance. Sudden death is possible.

    TVMDL has a serological test for Chagas disease which detects antibodies to T. cruzi the etiologic agent of Chagas disease. Detailed information on this test-Trypanosoma Cruzi (Chagas) IFA-is available online.

    If an animal is suspected of dying of Chagas disease, TVMDL’s Histopathology Section can examine heart tissue for evidence of a nonsuppurative myocarditis and protozoal amastigotes. In most lesions, areas of necrosis, fibrosis and mineralization are observed. Protozoal amastigotes are more numerous in young dogs dying of Chagas disease. The organisms are difficult to find in older dogs with the chronic form of the disease. Other lesions include centrilobular hepatic necrosis and pulmonary edema. Often, a necropsy is needed to positively identify Chagas as the cause of death. TVMDL offers necropsy services (Necropsy-Histopathology, and Necropsy-Canine or Feline) at the Amarillo and College Station laboratories. For submission, price and turnaround times, visit our website.

    Chagas disease is reportable to the Texas Department of State Health Services; the disease can affect humans as well as companion animals and livestock. For information on Chagas testing at TVMDL, contact the laboratory or visit tvmdl.tamu.edu.


    MM: thank you!

    1. Thanks for the Chagas insight. I’ve been reading up on this. I came to appreciate parasitology in college and predict that as climate change continues, we will see an increased need for parasitologists and related specialists.

      There is plenty to read regarding Texas and other persons reported to have Chagas, as in humans, tend to be traced to immigrants. I was wondering what you consider the best resource for finding the odds of contracting Chagas within other parts of the USA directly, not from living in Central or South America.

      I admit this is a selfish inquiry. I have had two sets of mystery bug bites this year. Just had a lyme titer this morning for a bite that I first noticed just as I arrived home from Kansas City. I live in Queens, NY. Also had what I can only presume were bites back in June in a Queens park, that caused bruising! Bizarre.

      It’s sort of a curse being both biology educated and prone to over worry.

      1. P.S. Inquiries to the CDC were useless. They regurgitate the info found on their website. While I appreciate not wanting to risk liability and not being able to diagnose, they really had zero to offer in terms of true risk assessment. And no practiced way of explaining that. Poor “customer service.”

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