Risk of transmission of hantavirus and leptospirosis through contact with rodents in urban environments
Analysis of hantavirus and leptospirosis associated with rodents, their ecological differences and the necessary prevention measures in urban and peri-urban environments.
Rodents represent a significant threat to public health in urban environments due to their ability to transmit various zoonoses. Among the most relevant diseases are hantavirus and leptospirosis, both with the potential to cause outbreaks in urban and peri-urban areas. For effective control, it is essential to distinguish between synanthropic rodents (human commensals) and wild rodents, since each group acts as a reservoir for different pathogens and requires specific control strategies.
Urban expansion into natural areas, inadequate sanitation conditions, and the growing interface between urban and natural environments create scenarios that are increasingly conducive to the transmission of these pathogens to human populations.
“URBAN EXPANSION INTO NATURAL AREAS, INADEQUATE SANITATION CONDITIONS AND THE GROWING INTERPHASE BETWEEN URBAN AND NATURAL ENVIRONMENTS CREATE SCENARIOS INCREASINGLY CONDITIONAL FOR THE TRANSMISSION OF THESE PATHOGENS.”
Argentina is currently going through one of the most critical hantavirus seasons in recent years. According to the latest National Epidemiological Bulletin (No. 791; SE 1; 2026), during 2025, 86 cases were confirmed with 28 deaths, recording a fatality rate of 33.6%, much higher than previous seasons (period 2019 to 2024), where fatality ranged, with regional variations, between 10% and 32%.
The Central region (Buenos Aires, Santa Fe and Entre Ríos) is at the outbreak threshold, concentrating 22 confirmed cases in the 2025/2026 season and representing 70% of national cases. The province of Buenos Aires is the epicenter of the current outbreak, with 35 confirmed cases during 2025 and a fatality rate of 34.3% (12 deaths). The city of La Plata registered the highest concentration with 11 confirmed cases. The areas of greatest concentration include La Plata and Berisso, the Paraná Delta and Islands, the Samborombón wetlands and peri-urban areas.
This situation highlights the urgency of correctly understanding the transmission mechanisms and real reservoirs of this disease, since the confusion between synanthropic and wild rodents can lead to inadequate prevention and control strategies.
“IN THE AMERICAN CONTINENT, ALL HANTAVIRUS THAT PRODUCE SPH ARE ASSOCIATED WITH NATIVE WILD RODENTS.”
Hantavirus in urban environments
Hantaviruses are RNA viruses and cause two diseases in humans transmitted by rodents: hantavirus pulmonary syndrome (HPS) and hemorrhagic fever with renal syndrome (HFRS). Each hantavirus species has a rodent species as an intermediate host and its transmission varies significantly between continents. In Europe and Asia, some hantaviruses such as Seoul virus are associated with Rattus norvegicus (brown rat) and Rattus rattus (black rat), which are typically urban synanthropic species and can cause FHSR, but in Latin America it is not the predominant hantavirus and no cases have been recorded in humans.
On the American continent, all hantaviruses that produce HPS are associated with native wild rodents, which are not synanthropic, although they can approach peri-urban areas when their natural habitats are disturbed by urban expansion. In our country, rodents of the genus Oligoryzomys, commonly called “long-tailed”, are the reservoirs commonly associated with the disease.
Its distinctive characteristics are the tail (between 11-15 cm) longer than the rest of the body (between 8-12 cm), rounded ears and ocher-colored fur with reddish hues. They are granivorous-herbivorous and nocturnal. Hantavirus is known to spread from rodents to humans; However, some reports from Argentina and Chile have noted that the Andes strain of hantavirus can cause human-to-human transmission of the disease, as documented as part of the 1996 outbreak in El Bolsón and Epuyén, in southern Argentina.
“CONFUSION BETWEEN SYNANTHROPIC AND WILD RODENTS CAN LEAD TO INADEQUATE PREVENTION AND CONTROL STRATEGIES.”
Transmission and risk factors
Transmission of hantavirus occurs mainly by inhalation of aerosolized viral particles present in urine, feces and saliva of infected rodents. In Latin America, this happens when wild rodents enter closed or poorly ventilated spaces such as peri-urban homes, sheds or rural warehouses in urban-rural transition zones. Unlike commensal rats that permanently inhabit urban buildings, wild rodents are occasional visitors attracted by the availability of food.
Although less frequently, transmission can also occur through bites or direct contact with infected rodents or their excreta, particularly when there are skin lesions. The main factor that increases the risk of contagion is urban expansion into natural areas, since it increases the probability of contact between humans and wild rodents. This risk is amplified by homes with structural deficiencies that facilitate the entry of rodents and by areas with dense vegetation that provide suitable habitat for these species. Occupations with the highest level of exposure include agricultural and forestry workers, cleaning and waste collection personnel in peri-urban areas, and Pest Management Professionals.
“THE MAIN FACTOR THAT INCREASES THE RISK OF CONTAGION IS URBAN EXPANSION INTO NATURAL AREAS.”
Clinical manifestations
In the current HPS outbreak in Argentina, an exceptionally high fatality rate of 33.6% has been observed, with differences by age group. The most frequent symptoms reported include fever greater than 38.5 °C (95% of cases), myalgia (71%), headache (57%), vomiting (52%) and arthralgia (48%). The severity of the condition is frequently related to late diagnosis, which is why health authorities emphasize the importance of early consultation in the event of compatible symptoms and a history of exposure to risk areas.
Leptospirosis and hantavirus: two zoonoses, two ecologies
The fundamental difference between both zoonoses is that leptospirosis is an urban disease transmitted by synanthropic rodents (commensal rats), while hantavirus, as I mentioned previously, is peri-urban-rural, transmitted by native wild rodents.
Urban synanthropic rodents, especially Rattus norvegicus, shed the bacteria (Leptospira interrogans) in their urine, contaminating water and soil. Transmission occurs through contact with contaminated water or soil, entering through skin or mucosal lesions. The disease is clearly associated with urban environments with poor health infrastructure. Urban flooding is the main risk factor by dispersing bacteria and increasing human exposure.
Leptospirosis presents a mild form (90% of cases) that is characterized by a febrile condition, while the severe form or Weil's disease (5-10%) manifests jaundice, kidney failure and hemorrhages, with mortality of 10-15%. There are key differences in the ecology of rodent reservoirs between both zoonoses. In the case of leptospirosis, synanthropic rodent species such as the brown rat (R. norvegicus), the black rat (R. rattus) and the house mouse (Mus musculus) permanently inhabit urban environments, since they depend almost exclusively on humans for their survival.
“LEPTOSPIROSIS IS AN URBAN DISEASE TRANSMITTED BY SYNANTHROPIC RODENTS, WHILE HANTAVIRUS IS PERIURBAN-RURAL, TRANSMITTED BY NATIVE WILD RODENTS.”
The main environmental factors that favor its proliferation are the presence of organic waste, stagnant water and deteriorated structures. In contrast, wild rodents that are hantavirus reservoirs, such as long-tailed rodents (Oligoryzomys spp.) and other native cricetids, inhabit natural environments with occasional forays into peri-urban areas. Their proliferation depends on the availability of vegetation, seeds and insects as food resources, while the disturbance of their natural habitats due to urban expansion increases interaction with human populations and, consequently, the risk of transmission.
Given these ecological differences, each zoonosis requires specific prevention strategies. For leptospirosis, control is based on: 1) integrated management of urban rodents, 2) improvements in drainage and sewage systems, 3) adequate management of solid waste, 4) protection measures during floods and 5) education about risks associated with contact with contaminated water. In contrast, hantavirus prevention focuses on: 1) environmental control in peri-urban areas, 2) maintenance of buffer areas between urban areas and natural habitats, 3) hermetic sealing of structures in peri-urban areas, 4) education on identification and risks of wild rodents, and 5) safe cleaning protocols in rural sheds and warehouses.
Challenges in the current urban context
Climate change is modifying the transmission patterns of these zoonoses in a differentiated manner. On the one hand, the increase in the frequency and intensity of urban flooding exponentially increases the risk of leptospirosis, while warmer temperatures extend the environmental survival periods of leptospires in water and soil. On the other hand, climate changes alter the ecology of wild rodents, modifying their population cycles and distribution areas, which increases contact with human populations in peri-urban areas and the consequent risk of hantavirus transmission.
Simultaneously, unplanned urban growth aggravates both problems: it generates precarious settlements where synanthropic rodents proliferate (increasing the risk of leptospirosis) and expands the urban-rural interface, intensifying contact with wildlife reservoirs of hantavirus. These diseases disproportionately affect the most vulnerable and low-income populations, evidencing a problem of health inequity.
The effective approach to these zoonoses requires a transdisciplinary integration that articulates human health, animal health (including wildlife ecology), environmental management, urban planning and social development. The current context of climate change and accelerated urbanization poses growing challenges that demand innovative and sustainable strategies based on the One Health approach, which recognizes the different ecologies of rodents and their pathogens as a starting point for specific interventions.
In this framework, continued research on the ecology of synanthropic and wild rodents, transmission dynamics and the effectiveness of differentiated interventions is essential to develop evidence-based public health policies. Reducing the risk of transmission of these zoonoses constitutes an essential component for building healthy, resilient and equitable urban environments, especially to protect the most vulnerable populations.