Visceral leishmaniasis, which has been thought of as a rural disease restricted to Brazil’s northeastern region up to the 1980s, is moving toward increasingly larger urban centers. Caused by the protozoan Leishmania infantum chagasi and transmitted by bites from the female insects that transmit it, mainly the phlebotomine sandfly species Lutzomyia longipalpis (known locally as the birigui), the disease is currently present in all major regions, with almost half of the cases (47%) concentrated in the northeast of the country, according to the Brazilian Ministry of Health (MS). In 2016, the MS registered 3,626 cases in humans and 275 deaths across the country. In 2017, the states of Rondônia and Amapá recorded the first cases of domestic dogs with leishmaniasis, and the cities of Florianópolis and Porto Alegre saw their first cases in humans.
Since São Paulo registered its first human cases in 1999 in the municipalities of Araçatuba and Birigui in the northwest of that state, visceral leishmaniasis has been spreading toward the coast. Of the 645 municipalities in the state of São Paulo, 177 have already had cases of dogs or people with visceral leishmaniasis. According to a study published in February 2017 in the journal PLOS Neglected Tropical Diseases, by 2020, the number of infected dogs is expected to increase in Balbinos, Sabino, and Guaimbê in the central region of the state as a result of its proximity to the Marechal Rondon highway, high temperatures, and the presence of the insects that transmit the disease; dogs act as reservoirs for the protozoa. The number of infected persons is also expected to increase in Luiziânia, Alto Alegre, and Santópolis do Aguapeí, in the west of the state, because of increased humidity and the combined presence of insects and infected dogs (see the maps).
“Visceral leishmaniasis is advancing because of the lack of information which would permit early diagnosis,” commented parasitologist Mauro Célio de Almeida Marzochi, a researcher at the Oswaldo Cruz Foundation (FIOCRUZ) in Rio de Janeiro, at a scientific meeting held by the São Paulo State Department of Health in late April at the University of São Paulo Medical School (FM-USP). In August and November of 2016, respectively, a 19-month-old boy and his four-year-old brother died from this disease when it was diagnosed late in Guarujá, on the coast of São Paulo. In 2017, Guarujá reported another case, along with Votorantim, a city in São Paulo State near Sorocaba; no deaths occurred.
“Lutzomyia longipalpis is well adapted to hot areas with more open vegetation, such as the Cerrado scrublands,” observes biologist Eunice Galati, a professor at the University of São Paulo School of Public Health (FSP-USP). “Deforestation and replacing native vegetation with monocultures can create unfavorable environments for this species, which finds an environment in the cities that allows it to survive.”
Visceral leishmaniasis initially manifests in humans as pallor, continuous fever, weight loss, cough, diarrhea, and swelling of the liver and spleen. It can be fatal in humans if left untreated because of the damage to the liver, spleen, and bone marrow caused by Leishmania. The mortality rate is considered high, 7.8% on average, and few medicines are available that are effective against this disease. The most common treatment is pentavalent antimony, which involves daily intramuscular injections for at least a month. Although it effectively eliminates the parasite, the side effects are intense: the medication can cause muscle aches, nausea, vomiting, kidney inflammation, and gastrointestinal, cardiovascular, and respiratory problems.
In areas where visceral leishmaniasis is transmitted, the full disease transmission cycle is not always recognized and includes insects that transmit the disease, dogs, and infected humans. Sometimes only infected dogs and insects are found; other times, only human cases appear, such as in Guarujá. Another situation that can occur is that only dogs and people with leishmaniasis are identified and not any of the known insect vectors. This was the case in Florianópolis, which recorded three cases in humans and 125 infected dogs in 2017.
From 2010 to 2012, biologist Fredy Galvis-Ovallos, a researcher at the FSP-USP, visited the municipalities of Embu das Artes and Cotia in São Paulo to look for the possible origin of cases of canine leishmaniasis, which have been registered in the region since 2003. Lutzomyia longipalpis was not present, but he found many examples of Pintomya fischeri, a species cited as a potential transmitter of Leishmania infantum chagasi. “Even if confirmed, P. fischeri has a lower transmission potential than L. longipalpis, which could explain the lack of human cases in these municipalities.” According to the World Health Organization (WHO), the parasite that causes the disease can be transmitted by approximately 30 species of biting flies around the world.
Visceral leishmaniasis is a problem typical of countries with precarious hygiene conditions, since the insects that transmit the illness reproduce in decomposing organic matter and garbage dumps. Of the 82 countries where it has already been identified, seven concentrated 90% of cases of the disease: India (6,249 cases in 2016), South Sudan (4,175), Sudan (3,810), Brazil (3,336), Ethiopia (1,593), Somalia (781), and Kenya (692). In 2015, the WHO registered 23,084 cases of people infected with visceral leishmaniasis worldwide.