The Most Dangerous Wild Creature

2024, Spring Adirondac

I often begin my wilderness first aid courses with a little quiz, to assess participants’ ability to recognize risk. A favorite question, rarely answered correctly, is, “What wild animal is responsible for the most human deaths?”

Bears? Not by a long shot. Sharks? Nope. Snakes? A much bigger problem, but still not correct. Give up? Mosquitoes.

Mosquitoes are vectors (carriers) of a number of viruses from the arbovirus family and at least one parasite. One of these organisms causes a disease, malaria, which kills over 600,000 people annually. Some mosquito-borne diseases occur regularly in New York State (“endemic”), and a number of others have been identified in New Yorkers who have traveled, including on “adventure” travel. For reasons I will outline, these problems are likely to get worse in the coming years.

Here is a brief summary of six serious diseases, all transmitted through mosquito bites, and all reported in New York in recent years.

West Nile virus (WNV) and eastern equine encephalitis (EEE): These two diseases are endemic in New York, transmitted by our own mosquitoes. Both diseases are characterized by fever, body aches, .and headache. While WNV is generally mild (even asymptomatic), EEE is fatal in as many as a third of patients. Both are transmitted between birds and humans, while EEE has a number of other mammalian hosts, including horses. When either of these infections progress, they are associated with severe headaches, delirium, seizures, and loss of consciousness.

WNV and EEE should be considered in any New York resident suffering an unexplained neurologic illness with fever and headache during mosquito season. No vaccine or specific treatment is available for either. Prevention and supportive care are all we can offer.

Chikungunya: Although this disease has been around for a long time, we’ve only recently started hearing about it. While death is quite rare, patients with chikungunya may have debilitating fever and joint pain. Until about ten years ago, the condition was only seen in the United States (including in New York) in travelers returning from endemic areas such as the Caribbean. Now, however, locally acquired cases are regularly reported in Texas and Florida.

Zika: This infection was in the news quite a bit a few years ago. While news reports have dropped, the disease has certainly not gone away. Although patients may have a mild (even undetectable) illness, the real danger is to unborn children. Mothers infected with the virus during pregnancy may give birth to children with severe birth defects. Other than avoidance, there is no vaccine or treatment for the infection or for the associated birth defects. There had been local, mosquito- borne transmission of zika in the United States, but this has not occurred recently. U.S. cases now are all acquired through travel. The Centers for Disease Control and Prevention has published helpful information for people who are pregnant contemplating travel (cdc.gov/pregnancy/zika/ protect-yourself.html).

Dengue: Dengue is another “tropical” disease now seen in the U.S. As with most arbovirus infections, fever a11d joint or muscle pain are the hallmarks of dengue. Some patients, however, progress to dengue hemorrhagic fever, with bleeding and dysfunction of many organs. More than 20,000 people die of dengue annually.

Malaria: Malaria causes more human death and misery on an annual basis than any infectious disease other than tuberculosis and HIV/ AIDS. The disease is caused by one of a few species of parasites (Plasmodium) which is transmitted between humans by mosquitoes. The organism infects red blood cells and, from there, can affect nearly every organ system. For every fatal case, many more people are disabled. Although there are medications that prevent and treat malaria, the organism has been displaying resistance to some of them.

While most malaria in the U.S. is also acquired during travel, transmission in Florida and Texas is increasingly being reported. Many regions with a significant malaria burden are also popular destinations for the adventure traveler; I recently had to take a malaria preventive medication during an expedition to Kilimanjaro. Anyone contemplating travel to such an area should consult with a travel or wilderness medicine specialist for the most up-to-date recommendations.

Mosquito-borne diseases are spreading into areas in which they have not been seen before. Why? Climate change. Although we tend to think of mosquitoes as a single group of creatures, there actually are thousands of species. Each of these has specific environmental conditions (heat and humidity) in which it thrives. In turn, each of the organisms causing mosquito-borne diseases has preferred species of mosquitoes in which they reside. As areas become warmer and wetter, new mosquito species carrying “new” diseases may come in.

Tom Welch, MD, is a physician at Upstate Medical University in Syracuse and an active member of the Wilderness Medical Society. He is a licensed professional guide and a certifying instructor for the Wilderness Education Association, and has guided groups in the Adirondacks, Montana, and Alaska. More information is available at his website and blog, adirondoc.com. Leonard Weiner, MD, SUNY Distinguished Professor of Infectious Diseases at Upstate Medical University, reviewed this column and provided helpful suggestions.

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Topics: Bears, Disease, Environmental Injuries, General First Aid, Insects & Spiders, Snake Bites, Vaccines