Tularemia

Tularemia, also known as rabbit fever, is a primary bacterial infectious disease caused by the bacterium Francisella tularensis. The organism is a gram-negative coccobacillus that can infect humans through multiple routes and presents with six recognized clinical variants. The disease derives its name from Tulare County, California, where it was first identified in 1911.

Clinical presentation varies considerably based on the portal of entry and bacterial dose, with six characteristic forms recognized: ulceroglandular (accounting for approximately 75% of cases), glandular, oropharyngeal, pneumonic, oculoglandular, and typhoidal variants. Common manifestations include fever, skin ulcers at the inoculation site, and regional lymphadenopathy. Pneumonic tularemia and throat or nasal sinus infections represent serious complications that may arise from hematogenous spread or primary inhalation exposure. The incubation period typically ranges from one to fourteen days, with most infections becoming apparent after three to five days. Diagnosis is established through blood testing or culture of infected tissue, though the organism requires specialized media such as buffered charcoal yeast extract agar for isolation.

Tularemia maintains a persistent but relatively low incidence in endemic areas across the Northern Hemisphere. In the United States, approximately 200 cases were reported annually between the 1970s and 2015, with the majority occurring during summer months when arthropod vector activity peaks. Males are affected more frequently than females, and the disease occurs most commonly among young and middle-aged adults. Rodents, rabbits, and hares serve as primary reservoir hosts, while waterborne transmission accounts for five to ten percent of all cases in the United States, including infections linked to aquatic animals such as seals.

The bacterium is transmitted primarily through arthropod vectors, including ticks of the genera Amblyomma, Dermacentor, Haemaphysalis, and Ixodes, as well as deer flies of the Chrysops genus, particularly Chrysops discalis. Ticks can remain infectious for over two years, while individual deer flies may transmit the organism for up to fourteen days following acquisition. Human infection also occurs through direct contact with infected animal tissues, ingestion of contaminated water, or inhalation of contaminated dust or aerosolized particles. Hunters face elevated risk due to potential inhalation exposure during carcass processing, and documented transmission has occurred from mowing lawns where infected animal carcasses were present. The disease does not spread directly between people.

Hunters face elevated occupational risk due to potential inhalation exposure during the skinning and processing of infected game animals. Males are affected more frequently than females, and the disease demonstrates a predilection for young and middle-aged adults in endemic regions.

Prevention strategies center on avoiding exposure to known vectors and infected animals. Personal protective measures include the use of insect repellent, wearing long pants, and prompt removal of attached ticks. Individuals should avoid disturbing or handling dead wild animals without appropriate protection. No human vaccine is currently available for general use, though the organism has been considered a potential bioterrorism agent.

Surveillance for tularemia must account for its diverse clinical presentations and multiple transmission pathways, which may result in underrecognition of cases presenting with atypical manifestations. The seasonal summer peak in temperate regions corresponds to peak activity of tick and deer fly vectors, providing a predictable epidemiological signal for monitoring. Laboratory confirmation requires communication with microbiology personnel to ensure appropriate specialized media are employed, as F. tularensis cannot be isolated on routine culture media due to its requirement for sulfhydryl group donors such as cysteine. Waterborne outbreaks represent a smaller but significant proportion of cases and may warrant targeted environmental monitoring in endemic areas.

1. 1 Wikidata. tularemia.
2. 2 Wikipedia. Tularemia - Wikipedia.

ICD-10

ICD-11

Total cases

262

Peak month

2025-08

Coverage

3 reporting countries · 2000-01-01 → 2026-05-09