Mosquitoes are more than just a nuisance—they can also spread harmful diseases to humans and animals. The MSU VDL tests for these diseases to help veterinarians and public health officials identify and track cases.
In Michigan, two mosquito-borne viral diseases—West Nile virus, or WNV, and Eastern equine encephalitis, EEE—pose a fatal threat to humans and animals, especially horses. While EEE cases primarily occur in the Eastern U.S., WNV is found throughout the United States.
Please include vaccination status when submitting equine samples and use our equine submittal form. See our test catalog for information on sample type, collection protocol, shipping requirements, and other important information.
For More Information
- Michigan Emerging Disease Issues website includes information on mosquito-borne diseases in Michigan and the Michigan Zoonotic and Vector-Borne Disease Mapper
- Michigan Weekly Arbovirus Summary includes detailed information about current human and animal cases of arboviruses in Michigan counties; year-end summary is provided at the end of the season
- Centers for Disease Control and Prevention provides national data and information on diseases spread by mosquitoes
- Equine Disease Communication Center has information about these and other infectious diseases in horses, including clinical signs, diagnosis, treatment, and prevention as well as real-time disease alerts
Confirmed Cases of EEE and WNV in Michigan Animals, 2024
The Michigan Department of Agriculture and Rural Development is reporting the eighth case of West Nile virus (WNV) in a domestic animal for 2024.
On October 24, 2024, a 29-year-old Quarter Horse mare from Van Buren County became ill with ataxia, weakness, and difficulties swallowing and controlling her tongue. The horse was tested and confirmed to have WNV. While the mare was unvaccinated against the disease, it was last known to be alive.
For more information on equine diseases, please visit the Equine Disease Communication Center. For more information on detections of mosquito-borne diseases in Michigan, please visit www.michigan.gov/emergingdiseases.
The Michigan Department of Agriculture and Rural Development is reporting the seventh case of West Nile virus (WNV) in a domestic animal for 2024.
On October 15, 2024, a 12-year-old Quarter Horse mare from Tuscola County became ill with ataxia and weakness, which progressed to being down with an inability to rise. The animal was later humanely euthanized. The horse was tested and confirmed to have WNV. While the mare was vaccinated in the past, it has been over a year since the horse was last vaccinated.
For more information on equine diseases, please visit the Equine Disease Communication Center. For more information on detections of mosquito-borne diseases in Michigan, please visit www.michigan.gov/emergingdiseases.
The Michigan Department of Agriculture and Rural Development is reporting the 13th case of eastern equine encephalitis (EEE) in a domestic animal for 2024.
On September 23, 2024, a twelve-year-old Percheron gelding from Clare County was found down with an inability to rise. Later, the gelding was humanely euthanized due to the severity of its illness. The horse was tested and confirmed to have EEE. The gelding was unvaccinated.
For more information on equine diseases, please visit the Equine Disease Communication Center. For more information on detections of mosquito-borne diseases in Michigan, please visit www.michigan.gov/emergingdiseases.
The Michigan Department of Agriculture and Rural Development is reporting the 12th case of eastern equine encephalitis (EEE) in a domestic animal for 2024.
On October 5, 2024, a one-year-old Quarter Horse gelding from Tuscola County became ill with staggering/falling and hypersalivating, which progressed into being hypermetric (overreaching with its limbs) and having altered mentation. Later, the gelding was humanely euthanized due to the severity of its disease. The horse was tested and confirmed to have EEE. The gelding was unvaccinated.
For more information on equine diseases, please visit the Equine Disease Communication Center. For more information on detections of mosquito-borne diseases in Michigan, please visit www.michigan.gov/emergingdiseases.
The Michigan Department of Agriculture and Rural Development is reporting two new cases of eastern equine encephalitis (EEE) in horses for 2024, bringing the total amount of EEE cases in domestic animals to 11.
One case occurred in a two-year-old Standardbred filly from Osceola County. On September 25, 2024, the horse started to act dull, which progressed into seizures and lateral recumbency (lying down on its side). Later, the filly was humanely euthanized due to the severity of its illness. The horse was later tested and confirmed to have EEE. The filly was unvaccinated.
The second case occurred in a two-year-old Standardbred filly from Osceola County (a different premises than the case above). On September 29, 2024, the horse became ill with lateral recumbency and a lack of bowel/bladder control. Later, the filly was humanely euthanized due to the severity of its illness. The horse was later tested and confirmed to have EEE. The filly was unvaccinated.
For more information on equine diseases, please visit the Equine Disease Communication Center. For more information on detections of mosquito-borne diseases in Michigan, please visit www.michigan.gov/emergingdiseases.
The Michigan Department of Agriculture and Rural Development is reporting the ninth case of eastern equine encephalitis (EEE) in a domestic animal for 2024.
On September 28, 2024, a five-year-old Miniature Horse mare from Wexford County became ill with being hypermetric (overreaching with its limbs) and seeking dark areas. The mare was last known to be alive and was unvaccinated against the disease.
For more information on equine diseases, please visit the Equine Disease Communication Center. For more information on detections of mosquito-borne diseases in Michigan, please visit www.michigan.gov/emergingdiseases.
The Michigan Department of Agriculture and Rural Development is reporting one new case of Eastern equine encephalitis (EEE) and one new case of West Nile virus (WNV) in horses for 2024. These detections bring the total amount of EEE cases in domestic animals to eight and the total for WNV to six.
The EEE case occurred in a four-year-old Standardbred gelding from St. Joseph County. On September 15, 2024, the horse became ill with being down with an inability to rise. Later, the gelding was humanely euthanized due to the severity of its illness. The horse was later tested and confirmed to have EEE. The gelding was unvaccinated.
The WNV case occurred in a one-year-old Standardbred gelding from Eaton County. On September 21, 2024, the horse became ill with tremors and hindlimb weakness. The gelding was subsequently tested and confirmed to have WNV. While the owner did vaccinate the horse in the spring, it did not receive a booster. The gelding was last known to still be alive.
For more information on equine diseases, please visit the Equine Disease Communication Center. For more information on detections of mosquito-borne diseases in Michigan, please visit www.michigan.gov/emergingdiseases.
The Michigan Department of Agriculture and Rural Development is reporting the seventh case of Eastern equine encephalitis (EEE) in a domestic animal for 2024.
On September 17, 2024, a nine-year-old Quarter Horse gelding from Menominee County became ill with ataxia, blindness, an unwillingness to move, and falling into lateral recumbency (laying on its side). The gelding was later humanely euthanized, tested, and confirmed to have EEE. The gelding was unvaccinated.
For more information on equine diseases, please visit the Equine Disease Communication Center. For more information on detections of mosquito-borne diseases in Michigan, please visit www.michigan.gov/emergingdiseases.
The Michigan Department of Agriculture and Rural Development is reporting the fifth case of West Nile virus (WNV) in a domestic animal for 2024.
On September 9, 2024, an eight-year-old grade gelding from Kent County became ill with fever, ataxia, and muscle fasciculations (brief, spontaneous contractions). Due to the worsening of the gelding’s symptoms, the animal was humanely euthanized. Subsequently, the horse was tested and confirmed to have WNV. The gelding was unvaccinated.
For more information on equine diseases, please visit the Equine Disease Communication Center. For more information on detections of mosquito-borne diseases in Michigan, please visit www.michigan.gov/emergingdiseases.
The Michigan Department of Agriculture and Rural Development is reporting one new case of Eastern equine encephalitis (EEE) and one new case of West Nile virus (WNV) in horses for 2024. These detections bring the total amount of EEE cases in domestic animals to six and the total for WNV to four.
The EEE case occurred in a five-year-old Quarter Horse gelding from Allegan County. On August 26, 2024, the horse became ill with ataxia, circling to the right, head pressing, and seizures. Later, the gelding was humanely euthanized due to the severity of its illness. The horse was tested and confirmed to have EEE. The gelding was reportedly vaccinated by a previous owner back in the spring.
The WNV case occurred in an 18-month-old Standardbred colt from St. Joseph County. On August 30, 2024, the horse became ill with fever, leaning to the left, and acting sedated. Due to the colt’s declining condition, the animal was humanely euthanized. The horse was subsequently tested and confirmed to have WNV. The colt was unvaccinated.
For more information on equine diseases, please visit the Equine Disease Communication Center. For more information on detections of mosquito-borne diseases in Michigan, please visit www.michigan.gov/emergingdiseases.
The Michigan Department of Agriculture and Rural Development is reporting a horse that was dually infected with two arboviruses, making it both the fifth case of Eastern equine encephalitis (EEE) and third case of West Nile virus (WNV) in a domestic animal for 2024.
On August 2, 2024, a two-year-old filly from Kalamazoo County became ill with fever, ataxia, and horizontal nystagmus (involuntary, rapid eye movement), which progressed to being down with an inability to rise. Later, the filly was humanely euthanized due to the severity of its illness. The horse was tested and confirmed to have EEE and WNV. The filly was currently vaccinated against both diseases.
For more information on equine diseases, please visit the Equine Disease Communication Center. For more information on detections of mosquito-borne diseases in Michigan, please visit www.michigan.gov/emergingdiseases.
The Michigan Department of Agriculture and Rural Development is reporting the fourth case of Eastern equine encephalitis (EEE) in a domestic animal for 2024.
On August 9, 2024, a six-year-old pony mare from Cass County became ill with muscle twitches, staggering, and an inability to walk. The mare was tested and confirmed to have EEE. While the horse was unvaccinated, the animal has recovered from the disease.
For more information on equine diseases, please visit the Equine Disease Communication Center. For more information on detections of mosquito-borne diseases in Michigan, please visit www.michigan.gov/emergingdiseases.
The Michigan Department of Agriculture and Rural Development is reporting the second case of West Nile virus (WNV) in a domestic animal for 2024.
On August 19, 2024, a three-year-old Morgan gelding from Washtenaw County became ill with an unusual stance and hindlimb paresis, which progressed to being down with an inability to rise. Due to the severity of the gelding’s symptoms, the animal was humanely euthanized. The horse was tested and confirmed to have WNV. The gelding’s vaccination status is unknown.
For more information on equine diseases, please visit the Equine Disease Communication Center. For more information on detections of mosquito-borne diseases in Michigan, please visit www.michigan.gov/emergingdiseases.
The Michigan Department of Agriculture and Rural Development is reporting the third case of Eastern equine encephalitis (EEE) in a domestic animal for 2024.
On August 12, 2024, a nine-year-old Quarter horse gelding from Lapeer County became ill with fever, walking in circles, head lifting, vocalizing, and absent reflexes. The gelding’s disease progressed, and the animal was humanely euthanized. The horse was tested and confirmed to have EEE. The animal was unvaccinated.
For more information on equine diseases, please visit the Equine Disease Communication Center. For more information on detections of mosquito-borne diseases in Michigan, please visit www.michigan.gov/emergingdiseases.
The Michigan Department of Agriculture and Rural Development is reporting the second case of Eastern equine encephalitis (EEE) in a domestic animal for 2024.
On August 4, 2024, a one-year-old Paint colt from Van Buren County became ill with a lack of coordination and standing with a wide stance. The colt’s disease progressed, and the animal was humanely euthanized. The horse was tested and confirmed to have EEE. The animal was undervaccinated.
For more information on equine diseases, please visit the Equine Disease Communication Center. For more information on detections of mosquito-borne diseases in Michigan, please visit www.michigan.gov/emergingdiseases.