Wild Rat Bites


Summary

Wild rats are commensal animals whose natural habitat is in and around human buildings: farms, cities, sewers, garbage dumps. In cities, wild rats are more common in neighborhoods of low socioeconomic status.

Wild rat bites are relatively rare, but their exact number cannot be determined because bites are greatly under-reported. People of all ages are bitten by urban wild rats, but the majority of rat-bite patients tend to be children. Most bites happen at night while the patient is sleeping. Rats tend to bite parts of the body that are exposed during sleep, like hands and fingers.

Rat bites are usually not severe: most bites are simply washed and the patient is immediately released. The infection rate of rat bites is very low -- about 2%.

Very rarely, a rat may transmit a disease such as rat bite fever or ratpox through a rat bite. Rats are not a rabies risk in the United States.


Are wild rat bites common?

It's difficult to estimate how common wild rat bites are, because animal bites tend to be under-reported. Probably less than 10% of all bites are brought in for medical care (Strassburg et al. 1981). Of bites that are brought in, one study found that only 41% are reported to health authorities (Beck 1981). Even dog bites are under-reported: in Pennsylvania, a study of children aged 4-18 years found that the rate of dog bite was 36 times greater than the rate reported to health authorities (Beck and Jones 1985).

Rat bites are greatly under-reported as well. Social Services visits to the homes of rat-bite patients showed that the patients' family members usually had unreported rat bites (Ordog et al. 1985).

In general, however, it appears that rat bites are relatively rare even in areas where rats are common. A survey of 1,363 people in Baltimore found that although nearly two-thirds of respondents (64%) reported seeing rats in streets and alleys, only 6% reported seeing rats inside residences, and only 1.2% had experienced any rodent bite (rat or mouse) in their lifetime (Childs et al. 1991).

Hirshhorn and Hodge (1999) found that the incidence of rat bites in Philadelphia was 2.12 bites per 100,000 people per year from 1974 through 1984, and 1.39 per 100,000 people per year from 1985 through 1996.


Where are wild city rats found?

Wild city rats are found in and around dwellings, alleys, sewers, and zoos (Childs et al. 1991, Farhang-Azad and Southwick, 1979). Rat infestations are associated with areas of low socioeconomic status (Davis 1949, Childs et al. 1991).

Childs et al. (1998) examined the environmental and social characteristics of the home blocks of 514 patients that had been bitten by rodents (81% of the bites were due to rats). The authors found that most people who had been bitten lived in poor inner-city neighborhoods. These high-risk neighborhoods were more crowded, had more residences per block, a higher percentage of rental units, and more vacant addresses than low-risk blocks. The populations tended to have a high percentage of ethnic minorities (except Asians), a large percentage of children and a low proportion of people over 65.

High-risk neighborhoods also tended to be near subways, waste stations, railroads and parks, which are all a potential source of refuge and food for Norway rats. However, living near noisy transportation and waste stations may also be a characteristic of less affluent neighborhoods (Childs et al. 1998).


Characteristics of rat bites

Men vs. women

Women were slightly more likely to be bitten than men (51.5% women vs. 48.5% men, Childs et al. 1998; 58% women vs. 42% men Ordog et al. 1985; 52% women vs. 48% men from 1974-1984, Hirshhorn and Hodge1999; 56.5% women vs. 42.6% men from 1985-1996, Hirshhorn and Hodge,1999).

Age

The average age of bite patients tended to be relatively young.

Hirshhorn and Hodge (1999) studied 622 rat bite cases on record in Philadelphia from 1974 to 1996. The study found that rat bites primarily affected children age five and younger, with a range of less than 5 to over 75 years of age.

Childs et al. (1998) found an older median age of 22 years with a range of under 1 year to 93 years.

Ordog et al. (1985) found that the average age of a bite patient was10.8 years, with a range of 5 months to 42 years. The majority (74%) of bite patients were under 15, while 45% percent were under five years old.

Sallow examined rat bites in Baltimore between 1948 and 1952. This study found that 60.5% of victims were under six years of age. Infants of less than one year accounted for 24.5%.

Richter (1945) studied rat bites in Baltimore between 1939 and 1943. This study found that 60% of rat bite victims were less than 1 year of age.

Race

During 1974 to 1996, Hirshhorn and Hodge (1999) found that 50% of rat bite victims were black, 28% were white, and 22% were of Asian or Spanish origin. Blacks and Hispanics were represented disporportinately as having a high risk of receiving a rat bite. Between these two groups, Hispanics had an incidence rate four times greater than blacks.

Socioeconomic status

More bites occur in neighborhoods with the highest percentage of families living below the poverty line and the highest percentage of unemployed people. There is a close association between the incidence of rat bites and poverty (Hirshhorn and Hodge 1999).

Infirmity and weakness

Ninety percent of Ordog's rat-bite patients were either children, or had a physical or mental disability such as diabetes, a psychiatric disorder, intoxication, or a prior wound (Ordog et al. 1985).

Bitten person's location

All of Ordog's (1985) rat bites occurred in the patients' own homes. Hirshhorn and Hodge (1999) found that 92% of bites occured in the home (67% single family dwellings, 25% multiple family dwellings), while the remaning 8% of bites occured in other structures (e.g. research laboratories and schools).

Hirshhorn and Hodge (1999) found that 53% of rat bite victims recorded between 1985 and 1996 (33% between 1974 and 1984) lived in a residence that was in poor physical condition and had poor sanitation ratings both inside and outside.

Bitten person's activity

Most people were bitten at night while they are asleep (72%, Ordog et al. 1985; 54.6% Childs et al. 1998; 86%, Hirshhorn and Hodge 1999; 100%, Richter 1945; 80%, Sallow 1953). One bite occurred when a patient tried to feed a wild rat by hand (Ordog et al. 1985).

Hirshhorn and Hodge (1999) found that most bites (83%) occured between midnight and 6 a.m.

Where on the body do rats bite?

Most bites were to extremities. This is because most people are bitten at night while they are asleep. Rats tend to bite the parts of the body that are exposed during sleep: the face, arms and hands.

Ordog et al. (1985) found that 70% percent of rat bites were to the upper extremeties: the arm, wrist, hand, or finger. Eighteen percent were to the lower extremities of leg, thigh, or buttocks. The remaining 14% percent of the bites were to the face. Most of these bites were to areas of the body exposed while the patient was asleep.

Childs et al. (1998) found that 59.8% of bites were to the upper extremities of arm, wrist, hand or finger. Twenty-eight percent were to the lower extremities of leg, foot, or toe, while 9.3% were to the head, face or neck. The remaining 2.4% were to the body and trunk.

Hirshhorn and Hodge (1999) found that 48.3% of bites were to the hand, 19.6% were to the head, 15% to the foot, and 9% to the leg.

Richter (1945) found that 48% of bites were to the hands and arms, 20% to the face, and 19% to the legs and feet.

Time of year

Hirshhorn and Hodge (1999) found that most bites (48%) occur from May through August.

Type of wound

Sixty-one percent of the bites were single or multiple punctures. Fourteen percent were lacerations (all less than < 1 cm), 12% were abrasions, 6% were ecchymoses (bleeding in the skin), 5% were hematomas (bruise), and 2% were fractures (one patient's fingertip was fractured). Twelve percent of patents received wounds of multiple types (Ordog et al. 1985).

Treatment and infection rate

Most rat bites were not severe. Childs et al. (1998) found that most bites were simply washed and 98% of 514 patients were immediately released. Ordog et al. (1985) examined 50 rat bite patients, and only one patient (2%) developed a bacterial infection that required antibiotics.

When bite wounds were swabbed, only 30% of the wounds had a positive bacterial culture. Of these, 43% were Staphylococcus epidermidis. The remainder were Bacillus subtillus, diphtheroids, and alpha hemolytic streptococcus (Ordog et al. 1985).

Victim profile summary

The victim of a rat bite is mostly likely to be a child of either sex of less than five years of age, often nonwhite. The victim is usually bitten on the face or arms while asleep at home in the bedroom some time between midnight and 8 a.m. Poor, younger children are bitten by rats more frequently than adults (Hirshhorn and Hodge 1999).


Diseases transmitted by rat bite

Diseases transmitted by rat bite are rare. In two surveys of 514 and 50 rat bite patients, no patient contracted a disease from the bite (Childs et al. 1998, Ordog et al. 1985).

Very rarely, a rat may transmit rat bite fever (Graves and Janda 2001, Grude 2001, Schuurman et al. 1998, Hagelskjaer et al. 1998, Hockman et al. 2000, Weber 1982) or ratpox/cowpox (Marennnikova et al 1988, Postma et al. 1991). Rabies from rats is very rare and has never been documented in the United States. However, a handful of cases of rabies from a rat bite have been recorded in Poland (Zmudziñski and Smreczak 1995, described in Wincewicz 2002), Israel (Gdalevich et al. 2000), Thailand (Kamoltham et al. 2002) and Surinam (Verlinde et al 1975).


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