South America is seeing a surge in cases of the mosquito-borne disease dengue during the southern hemisphere summer.Brazil this month has started spraying insecticide from trucks, while hospitals in Paraguay have set up night clinics to attend to the sick due to elevated dengue activity.

Argentina has recorded over 12,500 cases of the disease in the last month, according to the latest official health bulletin, a big jump versus the same period a year ago, leading to health warnings and shortages of insect repellent.

In Brazil, where dengue is often called breakbone fever for the severe joint pain it causes, cases have more than doubled in the first week of January compared to the same period last year. Brazil will become the first country in the world to offer a dengue vaccine through the public health system, which officials said could begin within days.

South America and beyond is seeing the spread of dengue exacerbated as rising temperatures and the El Nino weather pattern in the Pacific contribute to prolonged dengue seasons and the geographical spread of infections, scientists say.

“Climate change has expanded the range for mosquitoes to breed, both in the Americas and globally,” Thais dos Santos, who specializes in arboviral, or insect-borne, diseases at the Pan American Health Organization (PAHO), told Reuters. PAHO data shows that last year topped a previous 2019 record for dengue cases in the Americas, with some 4.2 million cases and 2,050 deaths. Much of that was in the so-called “Southern Cone” of South America.

Spread by mosquitoes, dengue outbreaks typically occur three to five years after a previous epidemic. The December-February southern summer months bring ideal hot and humid conditions for mosquitoes to breed, spreading the potentially deadly disease that can cause high fever, muscle pain and internal bleeding.

Nelson Diego, 37, who said”Today is one of the better days because I can still open my eyes,” he . “I had a lot of pain in my joints and couldn’t walk before.”