Rats are highly effective and pervasive vectors, serving as both carriers and reservoirs for a wide variety of human pathogens. They are implicated in the spread of over 35 distinct diseases globally, a number that continues to grow as research into zoonotic illnesses expands. Understanding how these common rodents contribute to disease spread is the first step toward mitigating the significant public health risk they represent.
Mechanisms of Pathogen Transmission
Rats transmit disease-causing agents through both direct and indirect means, facilitating the transfer of bacteria, viruses, and parasites. Direct transmission occurs when a person comes into physical contact with the infected rodent or its bodily fluids. This includes being bitten or scratched by a rat, which can introduce bacteria from the rodent’s saliva.
Exposure also happens through contact with rat excreta, as pathogens are shed in urine, feces, and saliva. When a person handles contaminated surfaces, food, or water, infectious agents can enter the body through the mouth or breaks in the skin. Inhalation of aerosolized particles from dried urine or droppings is a hazardous route, occurring when infested areas are swept or disturbed.
Indirect transmission involves an intermediary organism, most commonly ectoparasites living on the rat. Fleas, mites, and ticks often feed on infected rats and subsequently bite humans, passing the pathogen to the new host. The rat functions as a host that maintains the pathogen’s life cycle, and the ectoparasite acts as the vector that completes the transfer to humans.
Major Diseases Carried by Rats
One of the most infamous rat-borne illnesses is the Plague, caused by the bacterium Yersinia pestis, which is primarily transmitted through the bite of an infected rat flea. The rat serves as the reservoir, and when the rat population dies off, the hungry fleas seek out human hosts to feed upon. While rare in modern times, plague outbreaks still occur.
Hantavirus is a viral infection that causes severe respiratory or hemorrhagic diseases, depending on the strain and geography. This virus is shed in the rodent’s urine, droppings, and saliva. Humans become infected by breathing in airborne particles contaminated with these dried excreta. Disturbing a rat nest in a poorly ventilated area, such as a shed or attic, can create a dangerous aerosolized environment.
Leptospirosis is a bacterial infection caused by Leptospira bacteria, which is excreted in the urine of infected rats. The bacteria can survive for weeks in freshwater or wet soil, allowing it to contaminate water sources, mud, and food crops. Humans typically contract Leptospirosis when contaminated water comes into contact with broken skin or mucous membranes.
Rat-Bite Fever (RBF) is a bacterial illness caused by organisms like Streptobacillus moniliformis and is transmitted to humans through direct contact. This occurs most commonly via a bite or scratch from an infected rat. Less frequently, infection occurs through the ingestion of food or water contaminated with the rodent’s droppings or urine.
Practical Steps for Risk Reduction
Reducing the risk of pathogen transmission begins with eliminating the factors that attract rats to human habitats, primarily food and shelter. All human and pet food must be stored in containers with tight-fitting lids to prevent access. Garbage should also be kept in sealed, robust bins and removed frequently.
Exclusion is a preventative measure that involves sealing all potential entry points into a structure, as rats can squeeze through openings the size of a quarter. Inspecting the exterior for cracks, gaps around utility pipes, and holes near the foundation is necessary to block access. Materials like steel wool, hardware cloth, or cement should be used to permanently seal these vulnerabilities.
If a rat infestation is discovered, safe cleanup procedures are important to avoid aerosolizing pathogens like Hantavirus. Never sweep or vacuum droppings, nesting materials, or urine, as this disperses the viral particles into the air. Instead, the area should be thoroughly sprayed with a household disinfectant or a bleach solution and allowed to soak for at least five minutes before being wiped up.
During the cleanup process, wearing rubber gloves and a respirator mask is recommended to protect against direct contact and inhalation. After the contaminated materials are collected and sealed in a plastic bag for disposal, all surfaces should be disinfected again. Ensure outdoor food and water bowls are not left out overnight, as these can be contaminated by foraging rats.