Vector-Borne Diseases

What are VBDs?

Vector-borne diseases are illnesses caused by viruses, bacteria, and parasites that are transmitted to humans by vectors. Examples of vector-borne diseases include West Nile, Malaria, and Zika. 

A vector is any animal capable of transmitting infectious pathogens between humans, or from animals to humans. Mosquitoes, ticks, and fleas are examples of vectors in Wyoming.

West Nile virus

West Nile virus (WNv) is the most common mosquito-borne illness in the United States. It is a zoonotic disease, meaning animals are involved in the transmission cycle. Numerous bird species serve as reservoir hosts in the environment. Certain Culex mosquitoes that feed on infected birds will become infectious and be able to transmit the virus during their next blood meal. This could be another bird, or large mammals like humans and horses. Humans and horses are referred to as incidental or dead-end hosts, because they do not contribute to further transmission. This means that a mosquito that bites a human or horse infected with WNv will not become infected. 

The majority of people who become infected with West Nile virus are either asymptomatic or only have mild febrile symptoms. Approximately 1 in every 150 cases (less than 1%), however, can be quite severe. This form of WNv infection is known as neuroinvasive disease which can be very serious. 

Horses can become seriously ill or even die from WNv. Fortunately, WNv vaccines are available. Yearly WNv vaccines for horses are available from your veterinarian or local feed and tack store. Culex mosquitoes that can transmit WNv will sometimes breed in horse troughs. Be sure to clean out the water in your horse trough once a week during the summer to prevent this vector species from breeding on your property.‍

Other Diseases

When the District tests mosquito samples for West Nile virus, we are also testing for St. Louis Encephalitis virus (SLEV) and Western Equine Encephalitis virus (WEEV). Both of which are significantly more rare than West Nile virus. Like West Nile virus, WEEV can also impact horses. To read more about other diseases that may impact livestock or wildlife in Wyoming, visit the University of Wyoming State Veterinary Lab or the Wyoming Game & Fish Department. 

We often get asked questions about other mosquito-borne diseases such as Zika. Luckily, in Wyoming we do not currently have the invasive mosquito species (e.g. Aedes aegypti and Aedes albopictus) that are capable of transmitting Zika virus, as well as numerous others. We are constantly on the look out for invasive mosquito species through our extensive surveillance program.

To read more about other mosquito-borne diseases in the United States, visit the Centers for Disease Control and Prevention. To read more about other vector-borne diseases that can affect humans in Wyoming, visit the Wyoming Department of Health.