tularemia

tularemia. Tularemia is a zoonotic disease caused by the highly infectious bacterium Francisella tularensis. It is primarily a disease of wild animals, especially rodents, rabbits, and hares, but can be transmitted to humans through various routes. The disease has a wide range of clinical presentations, from localized skin ulcers to severe systemic illness, and is considered a potential agent of bioterrorism.

Overview

Tularemia was first described in 1911 in California following an outbreak of a plaguelike illness in ground squirrels. The causative bacterium was isolated in 1912 by Dr. George Walter McCoy of the United States Public Health Service from squirrels in Tulare County, California, which gave the disease its name. Francisella tularensis is a small, non-motile, aerobic coccobacillus that is highly virulent, requiring as few as 10 organisms to cause infection. Due to its high infectivity and potential for aerosol transmission, it is classified as a Tier 1 select agent by the Centers for Disease Control and Prevention. The bacterium has several subspecies, with subsp. ''tularensis'' (Type A) found in North America being the most virulent.

Causes and transmission

The disease is caused by infection with the bacterium Francisella tularensis. Humans can become infected through several mechanisms, often related to contact with infected animals or their environment. Common routes include the bite of an infected arthropod, such as a tick (particularly Dermacentor species), deer fly, or mosquito; direct contact with the blood or tissues of infected animals, especially while hunting or skinning; ingestion of contaminated water, food, or soil; and inhalation of infectious dust or aerosols, which can occur during activities like lawn mowing or farming. Major animal reservoirs in the United States include cottontail rabbits, jackrabbits, prairie dogs, and muskrats.

Signs and symptoms

The incubation period is typically 3 to 5 days but can range from 1 to 21 days. Symptoms vary depending on the route of infection and the subspecies of the bacterium. The most common form is ulceroglandular tularemia, characterized by a skin ulcer at the site of inoculation and painfully swollen lymph nodes. Other clinical forms include glandular (swollen lymph nodes without an ulcer), oculoglandular (infection of the eye), oropharyngeal (from ingestion, causing sore throat and abdominal pain), pneumonic (from inhalation, causing cough and chest pain), and typhoidal (a severe systemic form with high fever and prostration). Without treatment, symptoms can persist for weeks and complications such as pneumonia, meningitis, or sepsis may occur.

Diagnosis and treatment

Diagnosis is often challenging due to the nonspecific symptoms and requires a high index of suspicion. Confirmation is typically achieved through serologic tests like microagglutination or enzyme-linked immunosorbent assay (ELISA), which detect antibodies. Cultures from blood, lymph node aspirates, or other clinical specimens can grow the bacterium, but this requires specialized biosafety level 3 laboratories due to the infection risk. Polymerase chain reaction (PCR) assays are also used. The preferred treatment for severe infection is an aminoglycoside antibiotic such as streptomycin or gentamicin. For less severe cases or for post-exposure prophylaxis, oral antibiotics like doxycycline or ciprofloxacin are effective. Early antibiotic treatment is highly effective and reduces mortality rates significantly.

Prevention and control

Prevention focuses on avoiding exposure to the bacterium. Key measures include using insect repellents containing DEET or picaridin and wearing protective clothing to prevent tick and deer fly bites. Individuals should avoid handling sick or dead wild animals, wear gloves when handling potentially infected animals (e.g., while hunting), and ensure wild game is cooked thoroughly. Drinking untreated water from streams or lakes in endemic areas should be avoided. In laboratory or agricultural settings where exposure to aerosols is possible, proper personal protective equipment and dust control measures are critical. There is a live attenuated vaccine strain developed in the Soviet Union, but it is not currently licensed for general use in the United States.

Epidemiology

Tularemia occurs widely across the Northern Hemisphere. In the United States, cases are most frequently reported from states like Arkansas, Missouri, Oklahoma, and South Dakota, with an average of about 200 human cases reported annually to the Centers for Disease Control and Prevention. Major outbreaks have been associated with lawn mowing or landscaping in endemic areas, as in Martha's Vineyard. In Europe, countries like Sweden, Finland, and Hungary report cases, often linked to mosquito bites or contact with hares. In Asia, it is reported in regions like Siberia and Turkey. The disease shows seasonal variation, with tick-associated cases peaking in summer and rabbit-associated cases in winter hunting seasons. Category:Zoonotic bacterial diseases Category:Arthropod-borne diseases Category:Occupational diseases