Patients in southern Brazil are being diagnosed with a form of malaria that researchers have just discovered has crossed from howler monkeys living in the region. The discovery is expected to complicate local drives to eradicate the disease from the area.
It was thought that malaria had been eradicated in southern Brazil for at least half a century. That was until in 2006 some people started coming down with the disease. Since then, around 1,000 cases have been reported from parts of Rio de Janeiro state, in the south east of the country, known as the Atlantic Forest region.
It has been assumed that these people, who have frequently reported having traveled elsewhere, had been infected with the common variety of malaria known as Plasmodium vivax, and then returned to Rio de Janeiro state where the symptoms then developed. Out of 49 people diagnosed with malaria between 2015 and 2016, the researchers managed to carry out tests on 28 samples, and were surprised by the results, which are published in the journal Lancet Global Health.
They found that none of the patients were infected by P. vivax, but instead that all of them were infected by a closely related malaria parasite normally found in howler monkeys, known as P. simium. It turns out that all the people with the parasite had at some point in the recent past visited the Atlantic Forest for either work of recreation.
It was already known that P. simium infected the monkeys but up until now, it was not certain that it could also infect humans. It is thought that the howler monkeys living in the forest act as hosts for the parasite, and the bromeliads living in the canopy are perfect breeding grounds for the mosquitoes that act as the vectors.
Interestingly, the researchers suggest that this species of Plasmodium has been infecting people in this region this entire time. Because the symptoms are the same as the more common South American malaria parasite P. vivax, and detailed tests haven't available at a high enough resolution to distinguish the two, the monkey version has simply been consistently misdiagnosed as P. vivax.
The discovery that this new species is also infecting humans will now complicate the process of eradicating the disease. It is now clear that while it was thought that southern Brazil was malaria-free for 50 years, this was most likely not the case. The fact that wild monkeys are harboring the disease will certainly add challenges in future attempts.