Rodent-Borne Disease
Vector Control’s goal is to keep up to speed with these changes and carefully monitor the County for the presence of newly emerging diseases. Rodents, both commensal and wild, are regularly sampled for hantavirus, leptospirosis, and other diseases.
Hantavirus Surveillance
Hantavirus Pulmonary Syndrome is a respiratory illness caused by rodent urine and feces that becomes airborne and is then inhaled. One becomes ill if the aerosolized particles are contaminated with Sin Nombre virus (SNV). The deer mouse (Peromyscus maniculatus) is the principal reservoir host of Sin Nombre virus. Occasionally, deer mice will enter buildings and potentially expose human occupants to the virus.
In collaboration with the California Department of Public Health, the Alameda County Vector Control Services District conducts regular hantavirus surveillance in local parks, open spaces, and East Bay Regional Parks District land. The focus of the District is to increase awareness of the disease and reduce public exposure to deer mice. Sin Nombre virus has historically been detected in animals in Alameda County, however the risk to the public is low. If an animal does test positive, residents are notified, and warning signs are posted in the area.
Seoul Virus Surveillance
Seoul virus belongs to the Hantavirus family of rodent-borne viruses. It is transmitted from rats to humans after exposure to aerosolized urine, droppings, or saliva of infected rodents. Exposure can also occur from inhaling dust from their nests or bedding. The natural hosts for Seoul virus are the Norway rat (Rattus norvegicus) and the roof rat (Rattus rattus). The symptoms and signs of Seoul virus infection are not specific, but may include fever, headache, nausea, joint pain, cough, and a mild to moderate form of hemorrhagic fever with renal syndrome. In 2019, the Alameda County Vector Control Services District began a surveillance program for Seoul virus as part of its hantavirus program.
Plague Surveillance
Plague is a bacterial disease associated with certain rodents, other mammals such as coyotes, and their fleas. It is famously known as the “black death” and was responsible for killing millions throughout Europe during the Middle Ages. Although first detected in Alameda County in 1909, it was last found in 1981 in the eastern part of the County when a ground squirrel and two coyotes tested positive. In 2023, in conjunction with the California Department of Public Health, District staff initiated a plague surveillance program in small mammals (Peromyscus mice and ground squirrels) for the first time since 1981.
Leptospirosis Surveillance
Leptospirosis is a disease caused by a bacterium that spreads through the urine of infected animals. It can get into water and soil, where it can survive for weeks to months at a time. Various domestic and wild animals can carry the bacterium, and excrete it for months or even years. Humans can become infected through contact with urine from infected animals or contact with soil, water or food that has been contaminated with the urine from infected animals. Symptoms in humans range from mild to severe, with most cases going undetected. The District began screening commensal rats for leptospirosis in 2020.