Amazonian flies may be carriers of a new bacterium linked to Andean fever

A team working in Brazil’s Amazon National Park has detected DNA from a previously undescribed Bartonella bacterium in local sand flies.

The signal clusters genetically near to other species that are already tied to Andean bartonellosis. This serious infection can cause high fever or wart-like skin lesions in people.

The finding does not confirm human disease, and the researchers are clear about that. It does, however, sharpen attention on bartonellosis, an infection that can be caused by several different Bartonella species. These bacteria can live in blood and blood vessel linings for long periods.

DNA from bacteria that cause bartonellosis

Marcos Rogério André of the Faculty of Agricultural and Veterinary Sciences at São Paulo State University led the work in collaboration with Brazilian colleagues.

In their research study, the group screened 297 female sand flies collected along two forest trails between February 2022 and February 2023. They detected Bartonella DNA in 12.6 percent of tested insects.

The scientists then used a genetic test to look for Bartonella DNA in the insects and confirmed targets with additional markers to place the sequences on the bacterial family tree.

Two sequences grouped in a clade alongside Bartonella bacilliformis and Bartonella ancashensis, both of which link to human illness in the Andes.

Disease spreads through sand flies

“Bartonellosis is a neglected disease. The disease best known to health professionals is cat scratch disease, caused by Bartonella henselae,” explained Rogério André.

The CDC’s overview notes that different Bartonella species spread through fleas, body lice, or sand flies, and that bartonellosis is an umbrella term for several related infections.

A connection to Andean fever

Andean fever, also known as Carrion’s disease, is caused by Bartonella bacilliformis carried by sand flies. It is a two-stage illness with an acute blood infection, called Oroya fever, that has a high fatality rate. This is followed in survivors by a skin condition called Peruvian wart.

Another Andean species, Bartonella ancashensis, has been genomically characterized as a human pathogen that can produce verruga like disease.

Phlebotomine sand flies are small, blood feeding insects that can transmit several pathogens, including Leishmania parasites and some viruses. Only females bite because blood meals fuel egg development.

How the Brazilian signal fits

The Amazon DNA sequences did not match Peruvian strains exactly, yet they sat close to the B. bacilliformis and B. ancashensis branch on the bacterial phylogenetic tree. That pattern raises questions about whether related Bartonella circulate in lowland forests that have not historically reported Andean bartonellosis.

The work also expands the list of sand fly species that may carry Bartonella DNA. Several of the positive insects were from lineages that have no previous association with these bacteria in Brazil.

Doctors should watch for Andean fever

Clinicians in tropical regions often see patients with fever of unknown origin. This means that Bartonella infections can run under the radar, especially in people with other health problems that make symptoms vague or prolonged.

If future field studies connect a local Bartonella strain in Brazil with human infection, doctors may need to consider targeted testing in patients who have compatible symptoms and a history of sand fly exposure.

How the field has been moving

Peru-based investigators have reported Bartonella bacilliformis DNA in sand fly species other than the classic, high-altitude vectors, including Lutzomyia maranonensis.

Outside the Andes, Mexican teams have identified Bartonella DNA in sand flies from several states, suggesting wider ecological circulation.

The use of PCR helps detect genetic material in the sand flies. This is an early and useful signal of potential bacterial infection. However, it does not, by itself, prove that a sand fly species transmits viable bacteria to animals or people.

Vector competence requires additional tests, including experimental infection of insects, demonstration of bacterial survival through the gut, and evidence of passage to a vertebrate host during feeding.

The caution from the authors

“We’re detecting a strain here in Brazil that’s never been described and is very similar to two species of the Bartonella genus that cause disease in Andean countries. Despite this similarity, we don’t yet have information on whether it can cause disease with distinct symptoms,” noted Rogério André.

That measured stance matches the genetic results. It leaves room for field epidemiology, clinical surveillance, and isolation of the organism.

What comes next for Andean fever

The team plans to sample more sand flies across Brazilian biomes, and to analyze what animals the insects feed on to identify possible reservoirs. That work will clarify whether the Amazon genotypes circulate among bats or other mammals, and whether people are at risk.

In parallel, clinicians can bank paired blood samples from patients with unexplained fevers or persistent vascular skin lesions. These can be analyzed later, as new diagnostics become available.

Public health takeaways

People visiting caves and river trails where sand flies are active can reduce risk by using protective clothing, applying repellents as labeled, and staying in screened spaces. Those common sense steps will also lower exposure to Leishmania.

Local surveillance that integrates entomology, wildlife sampling, and clinical lab networks remains crucial when signals like this appear.

The study is published in Acta Tropica.

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