Vector-Borne Diseases and Climate Change

Vectors are organisms that carry diseases between people and other creatures. Mosquitoes and ticks are two common examples. Animals can also transmit diseases to people through direct contact, their bodily waste, or by vectors that carry a disease between animals and people.

Climate change is altering the geographic range of vectors, often expanding their range into new locations, and it is also expanding their seasonal ranges, lengthening the time of year that a vector can act to transmit infection. Expanded geographic and seasonal distributions will likely increase risk of disease exposure.

West Nile Virus is a disease transmitted by mosquitoes that may increase in the region. Hotter temperatures and heavy precipitation events can accelerate its transmission. While most people infected with West Nile Virus do not show symptoms, one in five people develop a mild illness called West Nile fever that can last three to six days. One in 150 people can become severely ill with encephalitis or meningitis. The disease is transmitted when mosquitoes bite infected birds and then bite people. Most infections occur between June and September. Preventing mosquito bites is key to staying healthy.

Incidences of tick-borne diseases in Montana are relatively rare, averaging only nineteen cases per year, some of which are associated with travel outside the state. However, climate change could increase exposure to ticks and tick-borne diseases in the region. It’s important to perform regular tick checks to decrease the risk of tick-borne disease.

Deer mice (Peromyscus maniculatus) can carry viruses that can cause Hantavirus Pulmonary Syndrome in people. Climate change may increase rodent populations, indoors and outdoors, especially when periods of heavy rains follow drought and when temperature and rainfall increases. According to the Center for Disease Control (CDC), American Indians account for about 18% of all Hantavirus cases in the United States. Hantavirus is a severe respiratory disease that can sometimes be fatal. In the Blackfeet community, we have had several members contract Hantavirus. Anyone who comes into contact with rodents carrying Hantavirus can become infected with Hantavirus Pulmonary Syndrome.

Exposure to, or breathing dust after stirring up fresh rodent urine, droppings, and nesting materials of deer mice can infect people with Hantavirus. This process is known as “airborne transmission“.

Living or working in rodent-infested settings can expose people to Hantavirus. The primary risk for exposure is rodent infestation in and around the home, including cabins, sheds, and outbuildings like barns, garages, and storage buildings. Opening buildings that have been closed for the winter introduces risk as well.

Read more about Hantavirus transmission on the CDC website here.

Who is most at risk?

A variety of factors can contribute to vulnerability to vector-borne diseases, and only a few are listed here. Outdoor activity and being close to mosquito or tick habitat can increase risk. For example, living near stagnant water might increase risk of mosquito-borne illnesses. Advanced age and being male are associated with being at higher risk for severe West Nile Virus infections. Occupations like construction, farming, ranching, and pest control work that require people to crawl into spaces that serve as rodent shelter (like under buildings), open dormant buildings or shift wood, lumber, or hay that has been sitting for a while (and that can serve as rodent shelter) could increase risk of Hantavirus. Campers and hikers can also be exposed to Hantavirus if they camp in rodent habitats or use infested trail shelters.

How can we adapt?

• Follow the 4 D’s of West Nile Virus prevention to help people avoid exposure. Avoid being outside at Dawn & Dusk. Use approved insect repellents (Deet) and wear long sleeves and pants (Dress) while outdoors to help protect against mosquito bites, and remove standing water near homes (Drain) to help decrease the number of mosquitoes near residences.
• Encourage people to use window screens and air conditioning in summer months to help keep mosquitoes out of houses.
• One idea resulting from climate and health discussions was to think about encouraging bat activity near standing water, since bats consume mosquitoes. Building bat houses is one way to invite bats into an area. More investigation is needed, however, since the decision to encourage bat activity would need to be weighed against risks from possible increased exposure to bats. Bats themselves can transmit disease.
• Consider managing mosquitoes by removing mosquito breeding sites and applying pesticides where necessary, while recognizing ecological costs of using these methods.
• Wear long pants and socks, use insect repellents, and inspect your skin regularly in the spring and summer months to help prevent tick bites. If a tick is found on the body, follow proper protocol to remove it.
• Take precautions to help people avoid Hantavirus. For example, remove outdoor clutter near homes to reduce risks from rodents. Locate woodpiles, lumber, and hay bales far from homes to help reduce rodents sheltering near human residences. Secure holes and gaps in homes to prevent rodents from entering.
• If mice droppings or nests are found in the home or outbuildings, follow recommended clean-up procedures.

Next, read about Water-related Illnesses and Climate Change.

Or, learn about climate change as a health opportunity.

Some of the content found on this page is summarized from the U.S. Global Change Research Program’s report, “The Impacts of Climate Change on Human Health in the United States“, the National Institute of Environmental Health Sciences’ “A Human Health Perspective on Climate Change“, and the Center for Disease Control and Prevention’s “When Every Drop Counts” to briefly describe some of the possible health outcomes that are most relevant to Blackfeet Country. This page does not include all possible health impacts and outcomes, nor does it include all possible risks and responses.