What is Dr. Zubair Khalid's research focus?

Dr. Zubair Khalid specializes in molecular virology, mRNA vaccine development, and computational biology, with a focus on avian pathogens like IBDV and Avian Reovirus.

Where is Dr. Zubair Khalid currently working?

Dr. Zubair Khalid is a Postdoctoral Research Associate at the University of Maryland (UMD), specifically within the Department of Animal and Avian Sciences.

Tularemia (Rabbit Fever): Symptoms and Transmission

Name: Tularemia (Rabbit Fever): Symptoms and Transmission
Creator: Dr. Zubair Khalid

By Dr. Zubair Khalid, DVM, MS, PhD · 2026-09-20

Tularemia, widely known as rabbit fever, is a bacterial zoonosis caused by Francisella tularensis, a gram-negative intracellular coccobacillus with an exceptionally low infectious dose of roughly 10 to 50 organisms by inhalation [1]. The disease moves between wildlife, arthropod vectors, and people through several distinct routes, and it can produce sudden death in lagomorphs while causing ulceroglandular or pneumonic illness in humans [2][3].

This article explains how rabbit fever disease spreads, what it looks like in animals and people, how veterinarians confirm a diagnosis, and which handling precautions reduce risk for owners, hunters, and clinic staff.

What Is Tularemia and What Causes It?

Scanning electron micrograph of a macrophage infected with Francisella tularensis bacteria — Francisella tularensis, the bacterium that causes tularemia, infecting a macrophage. Image: NIAID, CC BY 2.0, via Wikimedia Commons.

Francisella tularensis is a gram-negative, facultative intracellular coccobacillus [4][2]. It survives inside host cells, which helps it evade immune clearance and contributes to its virulence. The organism is fastidious in the laboratory, meaning it grows slowly and requires special media, and culture work carries a high risk of laboratory-acquired infection [1].

Two subspecies cause most human disease. Francisella tularensis subsp. tularensis is found almost exclusively in North America and produces more severe illness. Francisella tularensis subsp. holarctica is distributed across the Northern Hemisphere, mainly Europe and Asia, and is the only subspecies causing tularemia in Europe [5][6]. More than 250 animal species are susceptible to infection, with rodents and lagomorphs (rabbits, hares, and pikas) serving as key reservoirs [6].

The bacterium is not a parasite in the strict sense, but it behaves like many vector-borne parasitic and rickettsial organisms. It depends on an arthropod or animal host to complete its environmental cycle, and its persistence in water, soil, and tick populations keeps it circulating even when clinical cases are rare.

Transmission Routes of Rabbit Fever

Tularemia reaches animals and people through four main pathways. Each route shapes the clinical picture that follows.

Tick and Deer Fly Bites

Ticks and mosquitoes are the principal vectors in many regions [6]. In Europe, tick and mosquito bites dominate transmission, and in Sweden and Finland mosquito bites are a main route of human infection [7]. The bacterium can invade mammalian erythrocytes, and this invasion enhances colonization of ticks after a blood meal, which in turn supports transmission to mammals and persistence in the environment [4]. This red blood cell invasion step is one reason the organism maintains such an efficient vector cycle.

Contact With Infected Lagomorphs

Direct contact with infected rabbits and hares is a classic route. Leporids are primary sources of human infection in the Northern Hemisphere [8]. In a study of wild leporids in Algeria, F. tularensis DNA was detected in 19.44% of Cape hares and 13.15% of wild rabbits sampled after spontaneous death or hunting, and half of the PCR-positive animals carried known tularemia arthropod vectors [8]. Handling or skinning an infected carcass without gloves exposes skin and mucous membranes directly to bacteria.

Aerosol and Inhalation

Inhalation of contaminated dust or aerosolized material can cause pneumonic tularemia. The infectious dose by this route is very low, in the range of 10 to 50 organisms [1]. Activities that generate aerosols from contaminated soil, hay, or carcasses carry particular risk. The high infectivity and aerosol potential of F. tularensis are central to why it is handled under strict biosafety conditions.

Contaminated Water and Food

The epidemiology of F. tularensis holarctica is closely tied to aquatic environments. The organism persists in natural water, where its survival has been associated with biofilm and amoebas, and these can serve as sources for mosquito larvae [7]. Consumption of contaminated water or food is a recognized transmission route [5]. This hydrotelluric cycle helps explain why tularemia cases cluster near certain waterways and wetlands.

How Tularemia Spreads Between Animals and People

Wild lagomorphs and rodents act as reservoirs, and arthropod vectors move the bacterium between them. When a tick or deer fly takes a blood meal from an infected animal, it can pass the organism on at its next feeding. The erythrocyte invasion mechanism described above improves the bacterium's ability to colonize the tick gut and persist through the vector's life stages [4].

Humans are incidental hosts. They become infected when they intrude on this wildlife cycle through bites, direct contact, inhalation, or contaminated water. Interhuman transmission is exceedingly rare [6]. That single fact matters for owners and clinic staff. A person with tularemia is not a meaningful transmission risk to others in ordinary contact, but the environmental and animal sources around them remain hazardous.

Wildlife sentinel studies show how widely the organism circulates even where human cases are uncommon. In Denmark, testing of 717 cervids and 64 raccoon dogs found F. tularensis seroprevalence of 6.8% in cervids and 16.4% in raccoon dogs [9]. A nationwide Danish seroprevalence study of blood donors and tick-exposed individuals found an overall seroprevalence of 2.2% [10]. These figures describe past exposure rather than active disease, and they show that subclinical or mild infections likely go unrecognized.

Not every region carries equal risk. A study of 952 wild lagomorphs in southern Spain's Mediterranean ecosystems found no F. tularensis DNA, indicating absent or very low circulation there [11]. Risk is geographic and local, which is why exposure history matters so much in diagnosis.

Symptoms of Tularemia in Animals

Animal signs vary by species and route of infection. In lagomorphs, the disease can progress quickly.

Sudden Death and Gross Lesions

Infected leporids may be found dead with no prior signs. At necropsy, F. tularensis-infected animals in the Algeria study showed enlarged spleen in 12 animals, enlarged adrenal glands in 12, liver discoloration in 12, hemorrhages in 11, and pneumonia in 11 [8]. These findings overlap with many other causes of sudden death in rabbits, so laboratory confirmation is required.

Abscesses and Enlarged Lymph Nodes

Abscess formation and lymph node enlargement are consistent features of tularemia across species. In a captive Pallas' cat at an urban zoo, autopsy revealed icteric tissues and pinpoint foci in the liver, spleen, and all lung lobes, and PCR testing confirmed F. tularensis [12]. Additional cases were later identified in wild eastern cottontail rabbits found dead at the same zoo, and wild lagomorph exposure was the likely route [12]. This case shows how a single infected rabbit population can seed infection in captive animals.

Species Beyond Rabbits

Tularemia is not limited to lagomorphs. Fatal tularemia has been reported in stranded beluga whales in Cook Inlet, Alaska, where F. tularensis subsp. holarctica was confirmed by quantitative PCR and immunohistochemistry [13]. This finding broadens the known host range and reinforces that the organism circulates in diverse ecosystems.

Symptoms of Tularemia in Humans

Human disease takes several forms depending on how the bacteria enter the body. Two presentations dominate.

Ulceroglandular Tularemia

Ulceroglandular disease follows intradermal infection, typically from a bite or direct contact with an infected animal [2]. It produces a skin ulcer at the inoculation site plus regional lymphadenopathy. This form has a substantially lower mortality rate than the pneumonic form [2]. People who skin or handle wild rabbits bare-handed are at risk for this presentation.

Pneumonic Tularemia

Pneumonic disease follows inhalation or intranasal infection [2]. The mortality rate following pneumonic tularemia is more than ten times that of ulceroglandular disease [2]. A published case described a patient who developed pulmonary tularemia complicated by sepsis, lung abscess formation, and pleural effusion, with a hospital course further complicated by secondary multidrug-resistant infections [14]. Symptoms can mimic atypical or treatment-refractory community-acquired pneumonia, which is why a careful exposure history is essential [14].

Other presentations include oral and gastrointestinal symptoms, and lymph node involvement can be severe. One case presented as an isolated mediastinal mass initially thought to be a solid tumor, with necrotizing mediastinal and hilar lymph nodes ultimately attributed to tularemia [3]. Symptoms vary by route of infection, so clinicians must keep a high index of suspicion when exposure history fits [3].

Diagnostic Decision Flowchart

Confirming tularemia requires matching the exposure history and clinical signs to the right laboratory test. The table below organizes that decision process by exposure, signs, and preferred test.

Exposure history	Clinical signs	Preferred test	Notes
Tick or deer fly bite, ulcer at bite site, regional lymph node swelling	Ulceroglandular disease	Serology (ELISA, microagglutination, indirect immunofluorescence)	Antibody tests are key detection tools and suit later-stage disease [15]
Contact with wild rabbit or hare, skinning without gloves	Skin ulcer, lymphadenopathy, fever	Serology plus PCR on lesion or tissue	Leporids are primary sources of human infection [8]
Aerosol exposure, contaminated hay or soil, atypical pneumonia	Pneumonic disease, refractory pneumonia	PCR on respiratory specimen, then serology	PCR supports early detection [15]
Suspected animal case, sudden death or abscesses	Enlarged spleen, liver discoloration, pneumonia	PCR on spleen or tissue	Molecular methods detect F. tularensis DNA directly [11][8]
Ambiguous or overlapping symptoms with brucellosis	Nonspecific febrile illness	Combined serology (MAT and iELISA)	Combining serological methods improves diagnosis in patients with non-specific symptoms [16]
Confirmed or suspected case needing strain characterization	Any form	Whole-genome sequencing, SNP analysis, MLVA	Molecular typing supports outbreak investigation [15]
Any suspected culture request	Any form	Culture only in biosafety level 3 laboratory	Culture is hazardous and must be handled under BSL-3 conditions [6]

The flowchart below follows the same logic for a single suspected case.

flowchart TD
    A[Exposure or signs suspected] --> B{Vector bite or animal contact}
    B -->|Yes| C[Look for skin ulcer and lymph nodes]
    B -->|No| D{Aerosol or water exposure}
    D -->|Yes| E[Look for pneumonia signs]
    D -->|No| F[Review full exposure history]
    C --> G[Order serology and PCR]
    E --> G
    F --> G
    G --> H{Result positive}
    H -->|Yes| I[Confirm and report]
    H -->|No| J[Repeat or broaden testing]
    I --> K[Notify public health and manage exposure]

Why Diagnosis Is Difficult

Tularemia symptoms are nonspecific, and this is the central diagnostic challenge [15]. Early disease can look like influenza, bacterial pneumonia, or a simple skin infection. Culture is protracted and hazardous because of the organism's fastidious growth requirements and the high risk of laboratory-acquired infection [1]. Diagnostic cultures should be handled in biosafety level 3 laboratories [6].

Laboratory methods have improved. Enzyme-linked immunosorbent assay, immunochromatography, microagglutination tests, indirect immunofluorescence assays, and PCR remain key detection tools [15]. Molecular typing methods including whole-genome sequencing, single-nucleotide polymorphism analysis, multiple-locus variable-number tandem repeat analysis, pulsed-field gel electrophoresis, and matrix-assisted laser desorption ionization-time of flight enable precise genetic characterization and support outbreak investigations [15].

Newer platforms aim for faster, field-ready detection. Immunoassays and biosensors, including electrochemiluminescence and Surface-Enhanced Raman Scattering platforms, are being developed for point-of-care use, with nanomaterial-enhanced recognition and microfluidic integration [1]. These tools matter because early detection reduces the impact of both natural outbreaks and other exposure scenarios [1].

Cross-reactivity complicates serology. Brucella species and F. tularensis can produce overlapping clinical features, and co-seropositivity has been observed. In one study of 467 serum samples, F. tularensis seropositivity was 3.64% by both microagglutination and indirect ELISA, and co-seropositivity between smooth Brucella spp. and F. tularensis was seen in 4.07% of samples [16]. Combining serological methods improves accuracy in patients with nonspecific symptoms [16].

Handling Precautions for Rabbits and Wildlife

Prevention rests on interrupting the transmission routes described above. These steps apply to pet owners, hunters, trappers, wildlife rehabilitators, and veterinary staff.

Wear gloves when handling any wild rabbit or hare, and never skin a wild rabbit bare-handed.
Avoid aerosolizing material. Do not dry-sweep or use high-pressure air around carcasses, nesting material, or soil that may be contaminated.
Do not handle or bury carcasses with bare hands. Use gloves and place carcasses in sealed bags.
Control ticks on pets and check yourself after time outdoors in tick habitat.
Avoid drinking untreated surface water in areas where tularemia is known to circulate.
Keep wild lagomorphs away from captive animal areas. The urban zoo case showed that wild eastern cottontails found dead near a captive Pallas' cat were linked to its infection [12]. Pest management and disease surveillance of wild lagomorph populations in zoos are important preventive measures [12].
Report suspected cases to public health authorities. Tularemia is an occupational risk for zoo staff and laboratorians [12].

Veterinary clinics should treat any suspected F. tularensis isolate as a biosafety concern. Culture must be performed only in a biosafety level 3 laboratory [6]. According to the Merck Veterinary Manual, tularemia is uncommon in dogs and cats, and suspected cases should be managed with strict hygiene and prompt veterinary involvement [17]. VCA Animal Hospitals notes that tularemia can affect dogs and that prevention focuses on limiting exposure to wildlife and vectors [18].

Tularemia in Dogs and Cats

Tularemia in dogs and cats is uncommon but possible. According to the Merck Veterinary Manual, dogs can develop tularemia after contact with infected wildlife or vectors, and the disease should be considered when there is a compatible exposure history [17]. VCA Animal Hospitals advises that limiting a dog's contact with wild rodents and rabbits and controlling ticks reduces risk [18].

Cats that hunt rodents and rabbits may be exposed through bites or by eating infected prey. Any cat or dog with fever, enlarged lymph nodes, abscesses, or respiratory signs after wildlife exposure should be evaluated by a veterinarian. Because the organism is highly infectious, owners should tell the clinic about the exposure before bringing the animal in, so staff can take appropriate precautions.

The Biology Behind the Risk

Two features explain why F. tularensis is treated with such caution. The first is the low infectious dose, roughly 10 to 50 organisms by inhalation [1]. The second is the organism's ability to survive inside host cells and to persist under stress. F. tularensis produces a universal stress protein that contributes to persistence during growth arrest and superoxide stress, and this protein supports expression of antioxidant defense genes [19]. This stress tolerance helps the bacterium survive in the environment and inside host cells.

Erythrocyte invasion adds another layer. F. tularensis can invade mammalian red blood cells, and the red blood cell membrane protein Band 3 is required for this invasion, while Ankyrin-1 is also required and Glycophorin A impedes it [4]. The bacterial protein GcvT interacts with the cytoplasmic domain of Band 3 and is required for red blood cell invasion [4]. This mechanism links the bacterium directly to the tick feeding cycle.

Ecological niche analysis shows that different clades of F. tularensis holarctica occupy distinct ecological niches, which helps explain regional differences in case numbers and transmission patterns [20]. A changing climate expands the range in which ticks can live and may contribute to increasing tularemia case numbers [5].

Common Myths and Questions About Rabbit Fever

Several misunderstandings persist about rabbit fever disease.

Myth: Only rabbits carry tularemia. More than 250 animal species are susceptible, with rodents and lagomorphs as key reservoirs [6]. The beluga whale cases confirm that marine mammals can be infected [13].

Myth: You can only get tularemia from a tick bite. Tick and mosquito bites are major routes, but contact with infected animals, aerosol inhalation, and contaminated water or food all transmit the disease [5][7][8].

Myth: Tularemia spreads easily between people. Interhuman transmission is exceedingly rare [6].

Myth: A dead rabbit is safe to handle if it looks normal. Infected lagomorphs may be found dead with no prior signs, and gross lesions overlap with many other diseases [8]. Gloves and avoidance of aerosol generation are essential.

Myth: Dogs and cats cannot get tularemia. They can, though it is uncommon, and wildlife exposure is the main risk factor [17][18].

Limitations and When to Contact a Veterinarian

This article is educational and is not a substitute for veterinary diagnosis or treatment. Individual cases require a veterinarian who can examine the animal and review the full exposure history.

Contact a veterinarian promptly if any of the following apply:

A pet has had contact with a wild rabbit, hare, or rodent and develops fever, enlarged lymph nodes, abscesses, or breathing difficulty.
A dog or cat shows sudden lethargy, loss of appetite, or respiratory signs after time in tick habitat.
You find a dead wild rabbit on your property and your pet had access to the area.
You handled a wild rabbit or hare without gloves and develop a skin ulcer, swollen lymph nodes, or fever. Seek human medical care in that situation.
A pet's illness does not improve with standard treatment, especially if pneumonia is suspected. Atypical or treatment-refractory pneumonia may indicate uncommon organisms such as F. tularensis [14].

Diagnosis in animals relies on PCR and serology, and culture must be performed only under biosafety level 3 conditions [6]. Your veterinarian will decide which tests fit the case.

Frequently Asked Questions

What is tularemia rabbit fever?

Tularemia, also called rabbit fever, is a zoonotic bacterial disease caused by Francisella tularensis, a gram-negative intracellular coccobacillus [14][2]. It affects more than 250 animal species and can cause severe illness in humans.

How do people get rabbit fever?

People get rabbit fever through tick or deer fly bites, direct contact with infected lagomorphs, aerosol inhalation, and contaminated water or food [5][7][8]. The infectious dose by inhalation is very low, around 10 to 50 organisms [1].

Can you get tularemia from skinning a rabbit?

Yes. Direct contact with infected rabbits and hares is a classic transmission route, and leporids are primary sources of human infection in the Northern Hemisphere [8]. Never skin a wild rabbit bare-handed, and always wear gloves.

What are the symptoms of tularemia in humans?

The two main forms are ulceroglandular disease, with a skin ulcer and swollen lymph nodes, and pneumonic disease, which follows inhalation and has a much higher mortality rate [2]. Symptoms vary by route of infection and can mimic other pneumonias [3].

What are the signs of tularemia in rabbits?

Infected rabbits may die suddenly with no prior signs. Necropsy findings include enlarged spleen, enlarged adrenal glands, liver discoloration, hemorrhages, and pneumonia [8]. Abscesses and enlarged lymph nodes also occur.

Is tularemia contagious between people?

No. Interhuman transmission is exceedingly rare [6]. The main risk comes from environmental and animal sources, not from contact with an infected person.

How is tularemia diagnosed?

Diagnosis uses serology, PCR, and in some cases culture, guided by exposure history and clinical signs [15]. Culture is hazardous and must be handled in a biosafety level 3 laboratory [6].

Can dogs and cats get tularemia?

Yes, though it is uncommon. According to the Merck Veterinary Manual, dogs can develop tularemia after contact with infected wildlife or vectors, and tick control and limiting wildlife contact reduce risk [17][18].