Rodents are one of the most successful groups of mammals and have been able to exploit a wide variety of habitats and environments throughout the world. Although people have largely categorised rodents as pests in urban and agricultural environments, most rodent species live in the wild with little interaction with humans. A small minority of rodent species have adapted to live in close association with humans, using our agriculture and waste as their own food resources and finding our buildings can make good rodent homes. The close proximity of these rodents to human habitation means that they can spread and transmit diseases which affect people. The ability of rodents to carry and vector diseases is encouraged by their habits of utilising our waste and sewage, their mobility and the similar physiologies that humans and rodents share. Rodents are able to vector more than 60 known diseases, and the list grows as more research on zoonosis continues.

Plague is perhaps the most well-known rodent-vectored disease, due to the enormous impact it had on the human population of Medieval Europe when it was referred to as the Black Death. Although plague still exists and kills many people in many parts of the world, other rodent transmitted diseases such as Lassa Fever and Leptospirosis are potentially more serious in the numbers of people infected. There is growing concern from many experts around the world that zoonotic diseases are emerging and re-emerging, particularly in developing countries that lack the resources to investigate, manage and treat a number of diseases and the underlying reasons for their spread and persistence.

Potential socio-economic factors that may affect zoonosis transmission, particularly for developing country situations:

  • general hygiene at household and community levels
  • eating rats, frequently handling rats
  • food preparation methods, eating uncooked fruits and vegetables
  • food storage location and accessibility level, ranging from inside dwelling to rodent-proofed store
  • drinking water storage
  • source of drinking water
  • source of washing water - bathing, clothes, kitchen utensils
  • proximity to sewage
  • proximity to open water
  • proximity to agricultural land - vegetable or staple crops
  • proximity to bush or fallow land
  • amount of rodent harbourage inside home - notably nesting in thatched roofs, burrows in mud walls, roof or wall voids, behind furniture
  • amount of rodent harbourage outside relatively near home
  • density and quality of housing
  • occupation - paddy fields, slaughter houses, animal husbandry, activities that may increase cuts to hands and feet
  • wealth and education levels
  • gender and age

Rats and mice (commensal and wild) have significance for public health chiefly due to their role as carriers or reservoirs for infections and diseases that can be transmitted to humans (zoonoses). The diseases present in the Americas include: the plague (Yersinia pestis), salmonellosis (S. typhimurium; S. enteritidis); leptospirosis (L. icterohaemorragiae); murine typhus (Rickettsia typhi); rickettsialpox (R. akari); lymphocytic choriomeningitis (arenavirus); rat-bite fever (Spirilum minus, Streptobacillus monilifomis); Hantavirus hemorrhagic pulmonary syndrome; hemorrhagic fevers (Arenavirus); Venezuelan equine encephalitis (alphavirus); Powassan encephalitis (Flavivirus); rabies; Rocky Mountain spotted fever (R. rickettsii); and tularemia (Francisella tularensis), as well as parasitisms, such as trichinosis (Trichinella spiralis); eosinophilic meningitis (Angiostrongylius cantonensis); and taeniasis (Hymenolepis nana or H. diminuta).

The transmission of these infections to humans occurs by indirect contact. Some are transmitted through contact with infected rodent urine or feces, others through fleas and lice, and still others through mosquito bites.

Rodents and Mice in Natural Disasters

When natural disasters strike, rats and mice endure the same suffering as humans do. Many of them are crushed to death or drowned, die of starvation, or fall prey to infections. Their populations are frequently decimated. Moreover, there is often displacement among the survivors, who wander to new areas in search of protection, shelter, and food. Fearful and disorganized, it takes time for them to regroup and reorganize their social behavior, become familiar with their new environment, find safe havens, locate food and water, and memorize their movements. All this occurs before they reproduce again. Reproductive activity among wild rodents and commensal rats usually declines during the rainy season.

Colony building and reproduction only will begin when their new ecosystem has stabilized. Thus, the reestablishment of a rodent population after a disaster will take six to ten months under favorable conditions.

The infections carried by the new populations can be transmitted to people when the conditions favor contact with contaminated rodent urine or feces or with their ectoparasites, vectors of the infections. This contact also occurs between various species of commensal and wild rodents, permitting transmission and cases of emerging or heretofore unknown infections in new geographical areas.

In conclusion, during the emergency the spread infection by rodents will not be an immediate concern. However, the activity and growth of rodent populations should be monitored as part of the surveillance of these diseases.

Prevention of Diseaes transmitted by Rodents:

Community participation in both rural and urban areas is fundamental for the prevention of infections carried by rodents. A number of measures are recommended.

  1. Protect food from rodents. Insofar as possible, use containers (metal boxes, clay or ceramic pots with lids, silos). Large volumes of food or sacks should be placed on wooden benches in an orderly fashion to facilitate inspection of the sacks.
  2. Proper refuse and waste disposal. All materials that serve as a refuge for rodents–for example, cardboard boxes, idle machinery, wooden or brick troughs–should be removed from dwellings.
  3. In areas where leptospirosis has been detected, shoes must be worn. Keep people from bathing in stagnant water.
  4. General hygiene and sanitation. Dark, humid rooms and areas are undesirable; ensure that they receive adequate ventilation and light.
  5. Application of pesticides for fleas and lice.

Some of the Diseaes are:

Hantavirus Pulmonary Syndrome (HPS): Hantavirus pulmonary syndrome (HPS) is a deadly disease transmitted by infected rodents through urine, droppings, or saliva. Humans can contract the disease when they breathe in aerosolized virus. HPS was first recognized in 1993 and has since been identified throughout the United States. Although rare, HPS is potentially deadly. Rodent control in and around the home remains the primary strategy for preventing hantavirus infection.

Murine Typhus: Murine typhus (caused by infection with R. typhi) occurs worldwide and is transmitted to humans by rat fleas. Flea-infested rats can be found throughout the year in humid tropical environments, but in temperate regions are most common during the warm summer months. Travelers who visit in rat-infested buildings and homes, especially in harbor or riverine environments, can be at risk for exposure to the agent of murine typhus.

Rat-bite fever (RBF): Rat-bite fever (RBF) is a systemic bacterial illness caused by Streptobacillus moniliformis that can be acquired through the bite or scratch of a rodent or the ingestion of food or water contaminated with rat feces.

Salmonella enterica serovar Typhimurium: As its name suggests, it causes a typhoid-like disease in mice. In humans S. Typhimurium does not cause as severe disease as S. Typhi, and is not normally fatal. The disease is characterized by diarrhea, abdominal cramps, vomiting and nausea, and generally lasts up to 7 days. Unfortunately, in immunocompromized people, that is the elderly, young, or people with depressed immune systems, Salmonella infections are often fatal if they are not treated with antibiotics.

Leptospirosis: Leptospirosis is a bacterial disease that affects humans and animals. It is caused by bacteria of the genus Leptospira. In humans it causes a wide range of symptoms, and some infected persons may have no symptoms at all. Symptoms of leptospirosis include high fever, severe headache, chills, muscle aches, and vomiting, and may include jaundice (yellow skin and eyes), red eyes, abdominal pain, diarrhea, or a rash. If the disease is not treated, the patient could develop kidney damage, meningitis (inflammation of the membrane around the brain and spinal cord), liver failure, and respiratory distress. In rare cases death occurs.

Eosinophilic Meningitis: Eosinophilic meningitis is an infection of the brain occurring in association with an increase in the number of eosinophils, white blood cells that are associated with infection with worms that penetrate into the body. The organism most commonly causing eosinophilic meningitis is a rat lung worm called angiostrongylus cantonensis.

Sources: AAAnimal contro, OPS OMS, NRI

Related Posts