Brown Rat

Also known as the Norway rat and the common rat.

Rattus Norvegicus

Appearance

The head and body length is about 18cm and the weight is between 200 and 400g. Brown rats have coarse brown (occasionally black) fur, with a pale underside. They have a long sparsely haired tail that's shorter than the body, a blunt muzzle, stocky build and short ears.

Lifecycle

Brown rats usually have five litters per year with eight young per litter. Females become sexually mature at just 8-12 weeks, gestation is between 21 and 23 days, and females are able to conceive whilst suckling a previous litter, often mating within 18 hours of giving birth. They can breed throughout the year. Up to13 litters are possible each year, each one consisting of 7-9 young. The lifespan of a brown rat is up to 18 months in the wild, but can live 2-3 years.

Habits

Typically nocturnal, although they will sometimes forage for food during the day. They are burrowing rodents that are often found along building foundations or beneath rubbish. Brown rats usually travel within an area of about 100 to 150 feet in diameter when searching for food and water. They are omnivorous but prefer starch and protein-rich foods, such as cereals. Their diet includes meat, fish, vegetables, weeds, earthworms, crustaceans, nuts and fruit.

Disease

Rats are known to carry many diseases including Salmonellosis, Mycoplasma pulmonis, Tyzzer's Disease, Pasteurellosis, Pseudomoniasis, Murine Respiratory Mycoplasmosis (MRM), Cryptosporidiosis, Viral Hemorrhagic Fever (VHF) and Q fever.

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 the aerosolized virus from the rats breath. HPS is a potentially deadly disease.

Murine Typhus is (caused by infection with R. typhi) occurs worldwide and is transmitted to humans by flea-infested rats.

Rat-bite fever (RBF) is a systemic bacterial illness caused by Streptobacillus moniliformis and Spirillum minus that can be acquired through the bite or scratch of a rodent or the ingestion of food or water contaminated with rat faeces. Symptoms usually occur 2-10 days after exposure to an infected animal. Common symptoms include an abrupt onset of chills and fever, vomiting, pain in the back and joints, headache and muscle pain. By this time, the wound itself has usually already healed. Within 2-4 days after the onset of fever, a rash appears on the hands and feet. One or more large joints may then become swollen, red, and painful. Often clinical signs subside in several days but then recur at irregular intervals for weeks or months.

Salmonella enterica serovar Typhimurium is characterized by diarrhoea, abdominal cramps, vomiting and nausea, and generally lasts up to 7 days. Unfortunately, in the elderly, young, or people with depressed immune systems, Salmonella infections are often fatal if they are not treated with antibiotics.

Leptospirosis (Weil's Disease) is caused by bacteria of the genus Leptospira, and is transmitted by the urine of an infected animal. In humans it causes a wide range of symptoms including 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. Humans become infected through contact with water, food, or soil containing urine from these infected animals. This may happen by swallowing contaminated food or water or through skin contact. Symptoms appear after a 4-14 day incubation period. Up to 50% of severe leptospirosis cases are fatal.

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.

Staphylococcus aureus causes abscesses, boils and food poisoning. It can infect wounds and then spread further into the body and cause serious infections such as bacteraemia (blood poisoning) or toxic shock syndrome. Some strains of bacteria are resistant to the antibiotic methicillin. They are termed methicillin-resistant Staphylococcus aureus (MRSA), and tend to be far more complicated to treat. Getting this infection can be very serious.

Toxoplasma gondii is found in about 35% of rats but prefers to live in cats. In rats, the infection is usually contracted from eating cat faeces. The parasite then works itself into every organ in the rat's body especially the brain. There it remains viable for the lifetime of the rat, waiting for a cat to come along and eat the rodent which will then become infected. Toxoplasmosis is an infection that invades human tissue and can severely damage the central nervous system.

Dermatomycosis is a highly infectious fungus, particularly to children and the infirm. Dermatophytes affect a wide range of animals and are easily transmitted by direct contact with fungal spores.

Trichinosis is a roundworm infection transmitted from rats. Cysts hatch in human intestines and grow into adult roundworms. The worms can migrate into the blood stream and affect the lungs and brain.

Pseudotuberculosis (Corynebacteriosis) is a common and deadly infectious disease caused by mycobacteria, mainly Mycobacterium tuberculosis. Tuberculosis most commonly attacks the lungs (as pulmonary TB) but can also affect the central nervous system, the lymphatic system, the circulatory system, the genitourinary system, bones, joints and even the skin.

Aspergillosis is a rapidly invasive Aspergillus infection in the lungs that can cause repeated coughing up of blood, fever, chest pain, and difficulty breathing. Symptoms include fever, chills, shock, delirium, and blood clots. The person may develop kidney failure, liver failure (causing jaundice), and breathing difficulties. Death can occur quickly.

Streptococcosus is caused by the bacteria Streptococcus gallolyticus. Transmission to humans probably occurs by aerosols, ingestion or through the skin. Diseases in humans include streptococcal pharyngitis, pyoderma, abscesses, cellulitis, endocarditis, polyarthritis, pneumonia and septicemia.

Streptococcal toxic shock syndrome is a severe and often fatal disease characterized by shock and multiorgan failure. Early symptoms include fever, dizziness, confusion and a rash over large areas of the body. Death can occur within a few hours.