Outbreak status:
The World Health Organization (WHO) announced the first case of human infection with Western equine encephalitis virus in Argentina since 1996.
The organization said in a statement that Argentina reported the discovery of the first human case of infection with the virus on December 20th, which is considered “the first confirmed case of infection with this disease in more than two decades.”
Previously, cases of Western equine encephalitis were observed in Argentina in 1996 and during the period 1982-1983.
During the period between November 25th and December 27th, 2023, 1,182 cases of infection with the virus were detected in horses in 12 Argentine provinces.
According to the weekly national bulletin of the Ministry of Health of Argentina dated January 10th, 2024, there were nine additional laboratory-confirmed human cases, including another death.
About the disease:
It is an arboviral disease (i.e. a viral disease transmitted by arthropods, often insects) caused by the Western equine encephalitis virus, an alphavirus, which is closely related to the Eastern equine encephalitis viruses and the Venezuelan equine encephalitis viruses. Western equine encephalitis virus can cause serious and even fatal illness. Western equine encephalitis is most common in the plains areas of the western and central United States. It has also been reported in Central America and South America.
Method of transmission:
This virus affects both horses and humans and is spread by the bite of an infected mosquito. It spreads mainly by the Culex tarsalis mosquito. This mosquito can fly several miles from the place where it hatched. Apart from Culex tarsalis, Aedes and Culiseta mosquitoes can also transmit this virus.
Symptoms:
Symptoms of western equine encephalitis in humans usually appear 5 to 15 days after a mosquito bite. Usual symptoms include:
- Fever
- Headache
- Nausea
- Vomiting
- Poor appetite
- Fatigue and general weakness
Diagnosis and treatment of Western equine encephalitis:
If you live in or visit an area where this disease is common, you should be alert for any symptoms and consult your doctor if they occur. However, this disease has symptoms like many other viral encephalitis, and diagnosis is challenging. If your nervous system is affected, your doctor may admit you to the hospital and order some tests, such as:
- Lumbar spinal tap to examine cerebrospinal fluid (CSF)
- Computed tomography (CT) scan
- MRI scan
- Antibody tests
The first three tests will indicate the presence of encephalitis, allowing your doctor to plan your treatment. Antibody tests can specifically diagnose western equine encephalitis, but confirmation of positive results will take a few weeks.
There are no specific antiviral medications that are effective against Western equine encephalitis virus, so your doctor will prescribe supportive treatment to manage fever, pain, and other symptoms. Nervous system injury may require intensive care, including mechanical ventilation, controlling seizures, maintaining hydration, and managing increased pressure inside the skull (intracranial hypertension, which is a very serious condition).
Prevention of western equine encephalitis:
The American Association of Equine Practitioners recommends Western equine encephalitis vaccine as the primary vaccine for horses. Horses should be given regular vaccinations, usually annually, and you should work with your veterinarian to determine the appropriate vaccination schedule for the horse. Good vector control is also important to protect Horse Western equine encephalitis; Use insect repellent and protect horses at night when mosquitoes are most active, and mosquito breeding areas such as stagnant water, piles, and old tires should be eliminated.
The best way to protect yourself from this disease is to avoid mosquito bites. You should:
- Avoid outdoor activities during times when mosquitoes are most active: at dusk and dawn.
- Wear pants and long-sleeved shirts to cover as much of your skin as possible.
- Install screens on your doors and windows to prevent mosquitoes from entering.
- Sleeping inside a mosquito net. The net should be long enough to fit under the mattress.
- Apply insect repellent to exposed skin areas.
- Treat clothing, mosquito nets, and camping equipment with 0.5% permethrin. This insecticide kills or repels mosquitoes.
- Prevent mosquito breeding. This is done by emptying the water pools at least once a week. This includes bird baths, buckets, planters, flowerpots, litter boxes, and tires. Cover all water containers.
- Vaccinate horses.
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