Three Cabinet ministers in the administration of Bolivian leader Jeanine Áñez have also tested positive for the virus, including Health Minister Eidy Roca and Presidency Minister Yerko Nuñez, who is hospitalized.
The infections in Venezuela, Brazil and Bolivia, which is seeing a spike in cases, come after Honduran President Juan Orlando Hernández tested positive in June and was briefly hospitalized.
Áñez said she will remain in isolation for 14 days when another test will be done, but she will continue to work remotely from the presidential residence.
"I feel good, I feel strong," she wrote on her Twitter account.
Bolivia's Health Ministry says the Andean country has 42,984 confirmed coronavirus cases and 1,577 deaths, and is seeing a rebound in the number of new cases amid reports that hospitals are being overwhelmed in some regions.
In the highland city of Cochabamba, scenes have emerged of bodies lying in the streets and coffins waiting for days in homes to be taken away.
Bolivia is scheduled to hold a presidential election September 6. Áñez is running third in opinion polls. Former Economy Minister Luis Arce, who represents the party of ousted President Evo Morales, is in front, with ex-President Carlos Mesa in second.
In Venezuela, meanwhile, socialist party chief Diosdado Cabello revealed that he had tested positive for COVID-19, making him the highest-ranking leader in the distressed South American nation thus far to come down with the virus.
Cabello is considered the second-most powerful person in Venezuela after President Nicolás Maduro and made the announcement on Twitter, stating that he is isolated, getting treatment and will overcome the illness.
"We will win!" he wrote in conclusion.
Economically struggling Venezuela is considered one of the world's least prepared countries to confront the pandemic. Hospitals are routinely short on basic supplies like water, electricity and medicine.
The nation has registered considerably fewer COVID-19 cases than others in the region, but the number of infections has grown in recent weeks.
As of Wednesday, the government had reported 8,010 confirmed cases and 75 deaths.
Cabello was last seen Tuesday, when he met with South Africa's ambassador, Joseph Nkosi. Photographs released by the government showed him standing alongside and bumping fists with the diplomat while wearing a black mask.
The 57-year-old politician is head of the National Constituent Assembly, an all-powerful legislative body created by Maduro's government in 2017.
He had missed his weekly television program Wednesday, stating at the time that he was "fighting against a strong allergy" and resting.
Maduro said in a broadcast Thursday that Cabello's diagnosis was confirmed with a molecular exam - a test that is usually conducted with a nasal swab sample.
Venezuela has done far fewer of these tests than neighbouring countries, instead largely deploying rapid blood antibody tests. Some experts fear that relying so heavily on the rapid tests, which don't detect signs of illness early in an infection, means cases are being missed.
"Venezuela is with Diosdado," Maduro said. "I am sure soon enough we will continue on in this fight." In Brazil, President Jair Bolsonaro was diagnosed with COVID-19 on Tuesday.
He appeared Thursday on an online broadcast from the presidential residence as defiant as on previous occasions. He coughed once, but did not show other symptoms of the disease that has killed more than 69,000 people in the South American nation.
Bolsonaro repeated his view that the economic crisis brought on by the pandemic is more dangerous than the coronavirus itself. He insisted that mayors and governors need to reopen the country for business.
"We need governors and mayors, within their responsibilities, to reopen commerce. Otherwise the consequences will be harmful for Brazil," Bolsonaro said, wearing a gray shirt and sitting comfortably in front of two national flags. (AP) IND IND