Epidemiology | CDC Rabies

Epidemiology is the study of the distribution and causes of disease in populations. Epidemiologists study how many people or animals have a disease, the outcome of the disease (recovery, death, disability, etc.), and the factors that influence the distribution and outcome of the disease.

The epidemiology of rabies addresses several questions: what animals have rabies and in what regions of the country, how many people get rabies and from what animals, and what are the best strategies for preventing rabies in people and animals. Epidemiologic information is often presented as statistical data (e.g., numbers or percentages in graphs and on maps). For example, in 2001, 7,437 cases of rabies were reported in the United States. Raccoons accounted for almost 40% of reported cases.

United States rabies surveillance data, 2001
Each year, scientists from the Centers for Disease Control and Prevention (CDC) collect information about cases of animal and human rabies from the state health departments and publish the information in a summary report. The most recent report, entitled "Rabies surveillance in the United States during 2001," contains the epidemiologic information on rabies during 2001. This report can be found in its entirety in Professional Resources. Below is a brief summary of the surveillance information for 2000, including maps showing the distribution of rabies in the United States.

In 2001, 49 states, the District of Columbia, and Puerto Rico reported 7,437 cases of rabies in animals and no cases in humans to CDC (Hawaii is the only state that has never reported an indigenously accquired rabies case in humans or animals). The total number of reported cases increased by 0.92% from those reported in 2000 (7,369 cases).

map of distribution of rabies in raccoons

raccoon cases

skunk cases

bat cases

fox cases

map of distribution of rabies in coyotes

coyote cases

Wild animals
Wild animals accounted for 93% of reported cases of rabies in 2001. Raccoons continued to be the most frequently reported rabid wildlife species (37.2% of all animal cases during 2001), followed by skunks (30.7%), bats (17.2%), foxes (5.9%), and other wild animals, including rodents and lagomorphs (0.7%). Reported cases in raccoons and foxes decreased 0.4% and 3.5% respectively from the totals reported in 2000. Reported cases in skunks, and bats increased 2.6%, and 3.3% respectively from the totals reported in 2000.

Outbreaks of rabies infections in terrestrial mammals like raccoons, skunks, foxes, and coyotes are found in broad geographic regions across the United States. Geographic boundaries of currently recognized reservoirs for rabies in terrestrial mammals are shown on the map below.

map showing distribution of rabies reservoir animals in US

Domestic animals
Domestic species accounted for 6.8% of all rabid animals reported in the United States in 2001. The number of reported rabid domestic animals decreased 2.4% from the 509 cases reported in 2000 to 497 in 2001.

distribution of rabies by month during 2001

In 2001, cases of rabies in cats increased 8.4%, whereas those in dogs, cattle, horses, sheep and goats, and swine decreased 21.9%, 1.2%, 1.9% and 70.0% respectively compared with those reported in 2000. Rabies cases in cats continue to be more than twice as numerous as those in dogs or cattle. Pennsylvania reported the largest number of rabid domestic animals (46) for any state, followed by New York (43).


Dog cases	Cat cases	Cattle cases

Successful vaccination programs that began in the 1940s caused a decline in dog rabies in this country. But, as the number of cases of rabies in dogs decreased, rabies in wild animals increased, as shown in the graph below.

distribution of rabies cases by year 1955-2001

Human rabies
In this century, the number of human deaths in the United States attributed to rabies has declined from 100 or more each year to an average of 1 or 2 each year. Two programs have been responsible for this decline. First, animal control and vaccination programs begun in the 1940's have practically eliminated domestic dogs as reservoirs of rabies in the United States. Second, effective human rabies vaccines and immunolglobins have been developed . All human cases in the United States since 1990 are summarized in the Table of Human Rabies Cases from 1990- 2001. The case histories of the ten most recent deaths can be found using the links below.