Tularemia

Contents

Officials from the Center For Disease Control and Prevention (CDC) report that cases of tularemia, an uncommon disease found in rabbits and rodents, have increased by nearly 60% in the U.S. in the last ten years.

Caused by the bacterium Francisella tularensis, it was first discovered in Tulare County, California in 1911. Since then, tularemia has been found in every state except Hawaii. Cases are most common in the central United States, the Pacific Northwest, and parts of the East coast.

There are four subspecies of Francisella, differing in where they can be found and their ability to cause severe illness. F. tularensis type A is the most dangerous type and is only found in North America.

Luckily, tularemia is still relatively rare, with about 2,500 cases recorded in the U.S. between 2011 and 2022, mostly in warm weather months. Despite this, the family medic needs to know about infectious diseases they might encounter off the grid in times of trouble.

How Tularemia Spreads

Tularemia is often seen in rabbits, where it can cause mass die-offs in native populations. The infection is a known “zoonotic” disease, which means it can be spread from animals to humans.

How does tularemia end up in human victims? In the U.S., the bacterium is typically spread by dog, wood, and long star ticks, as well as deer flies. Contact with animals bitten by infected ticks and flies is also not uncommon. Francisella can also be found in water or soil; some humans catch it by drinking from contaminated sources or breathing bacteria-laden dust. Rarely, cases have been diagnosed in lab workers.

(Note: Recently, a marine biologist was infected after incurring an accidental cut while investigating a seal carcass. It’s the first known case seen in a marine mammal.)

Tularemia is problematic because of its very infectious nature. Francisella tularensis is so highly contagious that only 10-25 bacteria are needed to cause disease, entering the human body through the skin, eyes, mouth, or lungs.

Tularemia Signs and Symptoms

The incubation period for tularemia is usually 3-5 days, but ranges from 1-14 days. In most susceptible mammals, the clinical signs include high fever, chills, lethargy, loss of appetite, fatigue, muscle aches, chest discomfort, cough, severe sore throat, vomiting, diarrhea, and abdominal pain. The worst cases are life-threatening.

The exact symptoms in a particular human depend on where the bacterium originally entered the body. There are six variants:

Ulcero-glandular: This is the most common form of tularemia (75 percent of cases) and usually occurs following a tick or deer fly bite or after handing an infected animal. A skin ulcer appears at the site where the bacteria entered the body. The ulcer is accompanied by swollen lymph glands, usually in the armpit or groin.

ulcero-glandular tularemia ulcer

Glandular: Also commonly spread by ticks and deer flies, it appears similar to ulcero-glandular tularemia (but without the ulcer).

Oculo-glandular: This form occurs when the bacteria enter through the eye. This often happens when a person is dresses an infected animal and, then, touches their eyes. Symptoms include red, irritated eyes with swelling of lymph glands in front of the ear.

Oro-pharyngeal: This variant results from eating or drinking contaminated food or water. Patients may have a sore throat, mouth ulcers, tonsillitis, and swelling of lymph glands in the neck.

Pneumonic: This is the most serious form of tularemia. Caused by breathing in bacteria-laden dust, symptoms include cough, chest pain, and difficulty breathing. It can also occur when other forms of tularemia are left untreated and the bacteria spreads through the bloodstream to the lungs.

Typhoidal: This form is characterized by any combination of general symptoms without local symptoms (such as reddened eyes).

Diagnosis Of Tularemia

In normal times, diagnosis is by blood tests or cultures of the infected site. Off the grid, identifying tularemia is more complex, as many of the symptoms are very general. Be suspicious of any possible tick and deer fly bites, and any contact with contaminated soil or water. Handling sick or dead animals is another likely clue. The variants that cause a skin ulcer may be easier to diagnose.

Treatment of Tularemia

Bacteria such as Francisella tularensis are treatable with antibiotics, especially streptomycin, gentamicin, doxycycline, or ciprofloxacin. All of these drugs have side effects, so should be studied in more detail. Consider an antibiotic book like Alton’s Antibiotics and Infectious Disease for more information. Dosages and method of administration can be found below:

Age Category	Drug	Dosage	Duration (Days)
Adults	Gentamicin*	5 mg/kg IM injection or IV daily	10 – 14
	Ciprofloxacin*	400 mg IV or 500 mg PO (orally) twice daily	10 – 14
	Doxycycline	100 mg IV or PO (orally) twice daily	14 – 21
Children	Gentamicin*	2.5 mg/kg IM injection or IV 3 times daily	10 – 14
	Ciprofloxacin*	15 mg/kg IV or PO (orally) twice daily	10 – 14
	Doxycycline	2.2 mg/kg IV or PO (orally) twice daily	14 – 21

Prevention of Tularemia

tick bite

When hiking, hunting, camping, or working outdoors, it’s important to avoid the bites of ticks and deer flies:

Use Environmental Protection Agency (EPA)-approved insect repellents containing DEET, picaridin, IR3535, Oil of Lemon Eucalyptus (OLE), para-menthane-diol (PMD), or 2-undecanone. Of course, always follow product instructions.
Wear long pants, long sleeves, and long socks to keep ticks and deer flies off your skin.
Remove attached ticks promptly with fine-tipped tweezers.

In addition, don’t drink untreated surface water and stay away from blowing dust in areas where tularemia has been reported (or use a mask).

Closer to home, avoid mowing over dead animals. Check the area carefully before landscaping. If you hunt or keep rabbits, prairie dogs, muskrats, hamsters, and other related mammals, use gloves and, perhaps, masks. Cook any game meat thoroughly before eating.

Pets like domestic cats are very susceptible to tularemia and have been known to transmit the bacteria to humans. At present, however, no evidence of human-to-human transmission exists. No vaccine is available to the general public at the present time. Luckily, The death rate from the disease is less than 2 percent, but the CDC notes that severe variants may raise the level to as high as 24 percent.

One interesting note is that Francisella bacteria is considered a “tier-1 select agent.” This means it’s thought to be a toxin that has the potential for deliberate misuse against civilian population leading to mass casualty events. In other words, tularemia bacteria could possibly be used as a biological weapon. Read more in this article.

Joe Alton MD

Dr, Alton