Tularemia, also known as Rabbit Fever or Deer Fly Fever, is a highly contagious infectious disease that can affect both humans and animals. The agent responsible for the condition is the bacterium Francisella tularensis. Tularemia symptoms vary depending on the route of infection.
All types of Tularemia are characterized by fever, which can exceed 103F. This highly infectious bacterium is of great public health concern. This is due to its potential for use as a bioterrorism agent. It can cause life-threatening diseases and can be spread via aerosolization.
In the natural setting, rabbits, hares, and rodents are the species most susceptible to the disease. Having said this, it affects many other animals, both domestic and wild. Tularemia targets the skin, eyes, lymph nodes, gastrointestinal tract, and lung, and the disease presents in people with six known syndromes.
The 6 Types of Tularemia (Deer Fly Fever)
Ulceroglandular Tularemia is the most common form in people. A painful sore (ulcer) forms at the site where the bacteria enters the skin. This is generally the site of tick or fly bite. If the bacteria gain entry through abrasion or cut on the skin, it is usually on the hands and fingers.
The bacteria travel to local lymph nodes, causing swelling. On occasion, the puss can drain from the nodes. People who become infected also suffer fever, headaches, and general malaise.
The symptoms are similar to Ulceroglandular Tularemia, but no ulcer manifests.
Bacteria gain entry through one or both eyes. This results in inflammation of the eyes. The eye becomes painful, swollen, and red. There is discharge from the eye, and the person infected can become very sensitive to light.
This form of Tularemia results from touching or rubbing the eyes with contaminated hands or having infected material splash into the eye. As with other forms, there is swelling of the lymph nodes, and this is primarily seen in front of the ears.
Lesions of the gastrointestinal tract are the major feature of the oropharyngeal form of Tularemia. The gastrointestinal tract starts from the mouth, goes down the throat, esophagus, stomach, intestines, colon, and rectum.
Symptoms include mouth ulcers, sore throat, abdominal pain, vomiting, and diarrhea. In addition, the lymph nodes around the neck region become enlarged. The oropharyngeal form of Tularemia happens following ingestion of undercooked contaminated meat or contaminated water.
This is the most severe form of Tularemia. Symptoms include dry cough, chest pain, and difficulty breathing. A rash may also appear. The pneumonic form occurs following inhalation of dust or aerosols which contain the bacterium.
If left untreated, the other forms of Tularemia can progress to the pneumonic form. This happens when the bacteria gain entry into the bloodstream and spread to the lungs.
While the rarest form, Typhoid Tularemia, can be severe. There is no specific distinguishing feature. It can consist of any combination of the other forms of Tularemia. Infected people suffer a high fever, muscle and throat pain, and pneumonia. Sores and lymph node enlargement are not features.
What Are The Causes of Rabbit Fever?
Tularemia is caused by the bacteria Francisella tularensis. The disease is generally tick-born but can also be transmitted by deer flies. Less frequently, it spreads by aerosolization or direct contact with infected wild game. Contaminated food or water is the least reported source of infection.
Rabbit fever occurs in many countries across the northern hemisphere. It exists in every US state except for Hawaii but mainly in the south-central and western United States. Human to human transmission is not known to occur.
The most common forms of Tularemia (Ulcerogenic and Glandular) usually result from the bite of a tick or deer fly. In the United States, the American Dog Tick (Dermacentor variabilis), the Rocky Mountain Wood Tick (Dermacentor andersoni), and the Lone Star Tick (Amblyomma americanum) are capable of transmitting the bacterium.
The American Dog Tick exists east of the rocky mountains and limited areas on the pacific coast. Adult females are most likely to bite humans. This happens mainly in the spring and summer. The tick has a rugged exterior shield and is brown with white to gray markings.
As its name suggests, The Rocky Mountain Wood Tick lives in Rocky Mountain states. In addition to Tularemia, it is well known for its transmission of other tick-borne illnesses such as Rocky Mountain Spotted Fever and Colorado Tick Fever. The adult ticks are generally responsible for the transmission of F.tularensis to humans. This tick is dark brown, becoming grayish when engorged. It is oval and flattened in shape.
Of the three ticks known to harbor Tularemia, the Lone Star Tick wins the prize for spreading diseases. It is distributed across the eastern United States but seen most commonly in the south. The Lone Star Tick is very aggressive and will not hesitate to bite humans.
In addition to Tularemia, the Lone Star Tick is responsible for the spread of Ehrlichiosis, Heartland Virus Disease, Bourbon Virus Disease, and Southern Tick-Associated Rash Illness (STARI). However, the most distinguishing feature of the Lone Star Tick is the white dot (lone star) on the back of the adult female.
Deer flies (Chrysops discalis) also transmit Tularemia but do so less commonly than ticks. Nevertheless, they still serve as an important source of infection. They are distributed worldwide and inflict painful bites that cause welts. In addition, they have banded wings and brightly colored eyes.
Handling of infected animals also serves as an essential source of infection. Skinning infected game, especially wild rabbits or hares, releases bacteria. The bacteria then enter the skin through minor cuts or abrasions. A simple bite from a wild bunny or a rub of the eye or mouth after handling an infected animal can cause infection.
It can be near impossible to identify an infected rabbit, hare, or rodent. Because these animals are so severely affected, they are often simply found dead. Experimentally infected animals show signs like that seen in humans (fever, enlarged lymph nodes, ulcers). The disease generally lasts between eight to 14 days but ultimately ends in death.
At the opposite end of the spectrum, rabbit fever in dogs is rarely reported. Natural infection appears to occur, but clinical illness is either mild or not evident. When present, signs include transient fever, eye, and nasal discharge, and enlarged lymph nodes. There may also be a sore or ulcer at the site of entry. The disease in dogs generally resolves with supportive care.
F. tuarensis can survive for weeks in soil, water, and dead animals. The bacteria become airborne during gardening, farming, or any other activity that disturbs the soil. Inhalation of these airborne particles can cause Tularemia.
This is also seen with laboratory workers. Often laboratory workers conduct procedures that generate aerosols.
Waterborne outbreaks of Tularemia have been reported in Bulgaria, Georgia, Germany, Italy, Kosovo, Macedonia, Norway, Sweden, and Turkey. The majority happened after people drank contaminated water. Hunters and other people who eat wild animals may also become infected after eating meat that is not thoroughly cooked.
Associated Medical Complications of Tularemia
If left untreated, Tularemia can cause debilitating disease or even death. It can spread to many sites in the body, including the heart, liver, central nervous system, and bone. Medical complications can be fatal and include inflammation of the following organ systems:
- Lungs (pneumonia)
- The inner lining of the heart or valves (endocarditis)
- The outer covering of the heart (pericarditis)
- The membrane that lines the abdomen (peritonitis)
- Liver (hepatitis)
- Bone (Osteomyelitis)
- Tissue associated with the brain and spinal cord (Meningitis)
Diagnosis and Treatment of Rabbit Fever
The first clue of Tularemia generally involves one or more of the clinical syndromes. This is especially true if a tick or fly bite has occurred, there is a history of hunting or travel to an endemic area.
Confirmatory testing requires a culture of F. tularensis from tissue, body fluid, sputum, or blood. The bacterium is fastidious, and slow-growing; thus requires special culture media. Blood drawn for antibody testing is also used to confirm infection. Paired samples taken two to three weeks apart will prove seroconversion.
Supportive testing involves Polymerase Chain Reaction (PCR). This is a laboratory technique that amplifies segments of DNA. The benefit of PCR is that it offers a rapid result (generally less than 48 hours).
As a general rule, the antibiotics streptomycin or gentamicin is the preferred treatment. Chloramphenicol is added to streptomycin for the treatment of meningitis. Other less commonly used antibiotics include ciprofloxacin and doxycycline.
Besides antibiotic therapy, supportive care is also provided. If an abscess forms, it will need to be drained surgically. A warm compress can be applied to the eyes if the eyes are affected. Generally, headaches are managed with pain relievers.
Which Jobs Are Exposed to Tularemia?
Any job that increases exposure to wild animals or exposure within a laboratory setting increases a person’s risk of infection. Farmers, hunters, veterinarians, wildlife workers, landscapers, and meat handlers are at the highest risk.
The Effective Prevention of Rabbit Fever
You can prevent infection by taking a few simple measures to minimize exposure. Especially if in an endemic area:
- Do not skin or dress wild game with bare hands. Instead, wear rubber gloves and a face shield.
- Do not handle sick or dead animals.
- When entering tick-infested areas, cover any cuts or abrasions, especially if working outdoors.
- Wear insect repellent and clothing that covers exposed skin. Also, treat clothing and gear such as boots, socks, pants, and tents with a permethrin-based product. Do not allow your cat to come into contact with any permethrin-based products. Permethrin is highly toxic to cats!
- Perform a thorough search for ticks after leaving tick-infested areas. Search under the arms, in and around the ears, between the thighs, the groin region, belly button, and on the hairline and scalp.
- Shower immediately after being in tick-infested areas.
- Remove any ticks on you or your pets. Use fine-tipped tweezers to grasp the tick around the mouthparts. Pull upwards gently to avoid the mouthparts breaking away. Consult your doctor following tick removal about the care of the tick bite area.
- Ensure that household pets are on tick prevention recommended by your veterinarian.
- Ensure clean drinking water and fully cook meat before eating it.
The Danger of Tularemia Becoming a Bio-Weapon
The intentional release or threat of release of Tularemia is of great concern. It can cause debilitating or even fatal diseases. The ease of spread by aerosolization and high pathogenicity makes it a category A bioterrorism agent. It is among the top six highest risk agents known!
In summary, Tularemia is an infectious disease spread by ticks, deer flies, aerosol, or direct contact with infected animals. The bacteria responsible for the condition is F.tularensis. It targets multiple body organs, including skin, eyes, lymph nodes, nervous tissue, gastrointestinal tract, and lungs.
It causes disease in both humans and animals, with the most severe disease seen in rabbits, hares, and rodents. F. tularensis is found widely in the environment, but luckily manufacturing an aerosol weapon would require advanced laboratory procedures not accessible to most people.
Rochelle is a veterinarian board-certified in theriogenology (animal reproduction). She works as a general practitioner with a special focus on reproduction at Opelika Animal Hospital in Auburn Alabama. Rochelle always had a special affinity for animals growing up. As a veterinarian she is passionate about educating clients, empowering them with knowledge. This allows them to provide their pets the best preventive health care and embrace the human-animal bond.