As we humans take over and expand our activities into the remaining natural environment, we come into closer contact with more species of rodents and more diseases. Apart from rats and mice, other well-known rodents that can carry diseases and come into human contact include prairie dogs, groundhogs, ground squirrels, lemmings and voles. In fact, rodents are thought to be responsible for more deaths than all the wars over the last 1,000 years.
Leptospirosis is an infection caused by species of Leptospira bacteria. It is caught from the urine of infected animals, which include rodents and also cattle, pigs and dogs. Humans can become infected by:
Direct contact with urine or other animal body fluids (except saliva) of infected animals
Contact with soil, water or food contaminated with the urine of infected animals.
The bacteria live inside the animal’s kidneys and are passed out in urine. They can survive for weeks or months in soil or water. The bacteria do not only enter the body through the mouth, they can also enter through the skin, especially if broken by a scratch or cut, and the mucus membranes of the eyes, nose and mouth.
Leptospirosis occurs throughout temperate and tropical zones, but is more common in tropical and subtropical areas where the temperature and humidity are more favourable for its growth.
Rodents can carry Salmonella bacteria that cause illness in both humans and pets. Infection occurs by consumption of food or water contaminated with rodent faeces. The most common source of infection is by food contaminated with the faeces of farm animals. Genetic studies of Salmonella show that it is extremely complex and as a result has a complex classification. Symptoms of Salmonella include diarrhoea, fever, vomiting and abdominal cramps.
Typhoid fever (full name Salmonella enterica subsp. enterica serovar Typhi) is endemic in many developing countries where poor hygiene is widespread. It affects 27 million people a year, especially children. Humans are the only animal infected by this strain so it is unlikely to be transmitted by rats unless they come into direct contact with human faeces, for example in sewer systems. Typhoid can be treated with antibiotics and vaccines are available as protection from infection.
Rodents carry a wide range of disease-causing organisms, including many species of bacteria, viruses, protozoa and helminths (worms). Rodents can also carry several parasites and diseases at the same time. Rodents act as vectors or reservoirs for many diseases via their ectoparasites such as fleas, ticks, lice and mites, as well as some diseases carried by mosquitoes.
How do these rodent-borne diseases get transmitted?
Inhalation or direct contact with rodent excreta (urine, faeces, saliva)
Bites from rodents — microorganisms carried in saliva can infect both humans and other rodents
Drinking contaminated water or eating contaminated food
Rodents acting as sources for infecting ectoparasites (ticks, fleas, mites, lice) with various pathogens
Rodents can also act as reservoirs for various flying-insect-borne diseases