Argentina: Tick-borne bacteria detected in wildlife

Table of Contents

INTA specialists detected, for the first time in the country, the ‘Ehrlichia chaffeensis’ bacteria in swamp deer and in the ticks that parasitize them. This is direct evidence of the possible existence of an active transmission cycle of this zoonotic pathogen in Argentine wildlife. The study was recently published in the international journal Parasites & Vectors.

Ehrlichia chaffeensis is an intracellular bacterium transmitted by ticks to deer, canids, and humans. In infected people, it can cause human monocytic ehrlichiosis (HME), a disease with flu-like symptoms that may require hospitalization. Recently, a team of researchers from the Institute of Agrobiotechnology and Molecular Biology (IABIMO) INTA-Conicet detected the bacterium in specimens of swamp deer (Blastocerus dichotomus) and in ticks of the species Amblyomma triste that were parasitizing them, direct evidence of the possible existence of an active transmission cycle of this zoonotic pathogen in Argentine wildlife.

In 2008, the Hemoparasite Research Group of the Institute of Agrobiotechnology and Molecular Biology (IABIMO) INTA-CONICET had already reported the presence of this bacterium in Argentina by detecting it in ticks in the province of Santiago del Estero, the first evidence of E. chaffeensis in South America. However, the records were mostly based on ticks collected from the environment, with no direct connection to an infected host.

“In 2018, the bacterium Ehrlichia chaffeensis was found for the first time in deer populations in the swamps of Argentina. From an active surveillance in the health of these mammals that began to be carried out in the province of Corrientes and in the Delta of Buenos Aires, the bacterium was detected again in deer in different years,” explained Marisa Farber, head of the IABIMO specialized group.

As part of the Wildlife Health Surveillance project carried out by the research group of the Institute of Ecology, Genetics and Evolution of Buenos Aires (IEGEBA) led by Marcela Orozco at the Faculty of Exact and Natural Sciences of the UBA, for seven years, between 2018 and 2024, the researchers analyzed blood and tissue samples from swamp deer and parasitic ticks (A. triste) from the Paraná River Delta. Active surveillance was developed aimed at identifying potential wild hosts of the agent and understanding its transmission cycle in the area, and at the same time, work was carried out in a participatory manner on the early warning of wildlife mortalities. Faced with each notification, specialized teams traveled to the affected areas to carry out field studies.

From this work, E. chaffeensis DNA was identified in two samples of deer blood and in the salivary glands of three ticks that parasitized one of these animals. The methodological approach confirmed that it was an active infection in ticks and not traces of blood ingested during feeding.

“Since these early findings, we have made continuous surveillance efforts to better understand the ecological and epidemiological dynamics of this tick-borne zoonotic pathogen in the region,” explained Eliana Guillemi, IABIMO researcher and author of the paper.

The study also underlines the diagnostic complexity associated with this type of bacteria. “As it is an intracellular bacterium, it cannot be grown in the laboratory in a usual way, as in classical bacteriology,” explained Marisa Farber, an INTA specialist, adding: “That is why it is necessary to use molecular biology tools to detect its presence both in the mammal and in the vector that transmits it.”

After sequencing generic genes and a specific molecular marker, the team identified a genotype previously reported in Argentina. The detection of the pathogen in the salivary glands of ticks is especially significant, since these structures play a central role in the transmission of infectious agents to the host.

“This identification provides key evidence of a possible transmission cycle that connects the E. chaffeensis-positive swamp deer with ticks in Argentine wetlands,” said Guillemi, who explained that “it’s the first time that an infected host and a tick also positive for this bacterium have been detected together feeding on it, which strengthens the evidence of an active transmission cycle.”

The detection of E. chaffeensis in a highly biodiverse ecosystem reinforces the need for a comprehensive approach. “This underscores the urgency of sustaining integrated, multidisciplinary surveillance systems that monitor environmental, animal and human health as interconnected components,” Guillemi concluded.

Citation
#

The study Molecular detection of Ehrlichia chaffeensis in marsh deer (Blastocerus dichotomus) and their parasitic Amblyomma triste ticks in Argentina suggests a local transmission cycle was published in Parasites Vectors, National Library of Medicine from de NIH of United States. Authors: Eliana Carolina Guillemi, María Marcela Orozco, Iara Figini, Paula Blanco, Marisa Diana Farber.

PMID: 41484667 PMCID: PMC12866569 DOI: 10.1186/s13071-025-07211-1

Contact [Notaspampeanas](mailto: notaspampeanas@gmail.com)