RIO DE JANEIRO, Jan. 23 (Xinhua) -- At least 25 people have died from an outbreak of yellow fever since December in Brazil's second most populous state of Minas Gerais, the regional Health Department said on Tuesday.

Another 22 people have contracted the virus in the southeastern state, where 87 potential cases are being monitored, and 12 deaths are being analyzed.

Half of the deaths took place in the metropolitan area of the capital Belo Horizonte. Nearly all of the victims have been men, and most were not vaccinated against the disease.

The outbreak has spread to the neighboring states of Sao Paulo, the most populated, and Rio de Janeiro, which receives the most tourists.

In the city of Sao Paulo, authorities closed the zoo, zoo safari and botanical garden after a howler monkey infected with the virus was found dead.

Primates are the main carriers of the virus, which is transmitted via mosquitoes.

An earlier outbreak at the end of 2016 and start of 2017 in Minas Gerais claimed scores of lives.