A 66-year-old man has died from a rare mosquito-borne disease in Argentina, the national health ministry confirmed on Saturday. Six out of the 12 Western equine encephalitis cases registered so far, including the man who died, are in Santa Fe province.

The man lived in a rural area of Santa Fe and had diabetes, according to the latest health ministry epidemiology report. He started to experience symptoms at the end of November.

Most cases to date have been in men between 30 and 72 years old, although the disease has also been diagnosed in a 9-month-old baby. All of the patients were hospitalized and four of them are still receiving medical attention.

Western Equine Encephalitis (WEE) is a rare disease caused by a virus spread by mosquito bites. While it mostly infects horses, it can also be transmitted to humans. Human-to-human infections are not possible. Symptoms include fever, sudden headaches, tiredness, shivers and feeling generally unwell, and usually clear up after seven to 10 days.

The incubation period in humans ranges from two to 10 days. Most people do not experience any symptoms, the health ministry said in a press release.

Mosquitoes are the main vector, although birds act as a reservoir and can transmit the virus to other countries. “Humans and equines act as the final reservoirs of the virus, incapable of transmitting the virus to mosquitoes,” the World Health Organization said in a December 28 press release addressing the situation in Argentina.

Argentina’s National Agricultural and Food Health Service (Senasa, by its Spanish acronym) reported the first case of WEE in a horse on November 25. Three days later, the health ministry declared a nationwide epidemiological alert. The first human case in 27 years was reported on December 20 in the city of Reconquista in Santa Fe province. The last time a person was diagnosed with this disease in Argentina was in 1996. There was a previous outbreak in 1982 and 1983.

In the current outbreak, Senasa has reported over 1,000 cases in horses, affecting 15 of Argentina’s 24 provinces so far.

Argentina’s health authorities are recommending that the general public take measures to stop mosquitoes from breeding, including clearing weeds and emptying vessels such as plant pots and old tires where water could stagnate. People should also protect themselves from bites with measures such as spray, nets and coils, especially in rural areas. 

A mosquito invasion has been affecting the Buenos Aires Metropolitan Area for the past week. The Aedes albifasciatus mosquitoes invading the area spread WEE. However, they do not carry dengue fever — cases of this are also rising in some parts of the country, as is usual during the Argentine summer. Dengue is spread by the Aedes aegypti species.