Tularemia
Tularemia, also known as rabbit fever, is an infectious disease caused by the bacterium Francisella tularensis.[4] Symptoms may include fever, skin ulcers, and enlarged lymph nodes.[3] Occasionally, a form that results in pneumonia or a throat infection may occur.[3]
Tularemia
bacterium Francisella tularensis (spread by ticks, deer flies, contact with infected animals)[4]
Blood tests, microbial culture[5]
Insect repellent, wearing long pants, rapidly removing ticks, not disturbing dead animals[6]
Generally good with treatment[4]
~200 cases per year (US)[7]
The bacterium is typically spread by ticks, deer flies, or contact with infected animals.[4] It may also be spread by drinking contaminated water or breathing in contaminated dust.[4] It does not spread directly between people.[8] Diagnosis is by blood tests or cultures of the infected site.[5][9]
Prevention is by using insect repellent, wearing long pants, rapidly removing ticks, and not disturbing dead animals.[6] Treatment is typically with the antibiotic streptomycin.[9] Gentamicin, doxycycline, or ciprofloxacin may also be used.[5]
Between the 1970s and 2015, around 200 cases were reported in the United States a year.[7] Males are affected more often than females.[7] It occurs most frequently in the young and the middle aged.[7] In the United States, most cases occur in the summer.[7] The disease is named after Tulare County, California, where the disease was discovered in 1911.[10] A number of other animals, such as rabbits, may also be infected.[4]
Signs and symptoms[edit]
Depending on the site of infection, tularemia has six characteristic clinical variants: ulceroglandular (the most common type representing 75% of all forms), glandular, oropharyngeal, pneumonic, oculoglandular, and typhoidal.[11]
The incubation period for tularemia is 1 to 14 days; most human infections become apparent after three to five days.[12] In most susceptible mammals, the clinical signs include fever, lethargy, loss of appetite, signs of sepsis, and possibly death. Nonhuman mammals rarely develop the skin lesions seen in people. Subclinical infections are common, and animals often develop specific antibodies to the organism. Fever is moderate or very high, and tularemia bacilli can be isolated from blood cultures at this stage. The face and eyes redden and become inflamed. Inflammation spreads to the lymph nodes, which enlarge and may suppurate (mimicking bubonic plague). Lymph node involvement is accompanied by a high fever.[13]
Diagnosis[edit]
Pathology[edit]
In lymph node biopsies, the typical histopathologic pattern is characterized by geographic areas of necrosis with neutrophils and necrotizing granulomas. The pattern is non specific and similar to other infectious lymphadenopathies.[22]
The laboratorial isolation of F. tularensis requires special media such as buffered charcoal yeast extract agar. It cannot be isolated in the routine culture media because of the need for sulfhydryl group donors (such as cysteine). The microbiologist must be informed when tularemia is suspected not only to include the special media for appropriate isolation, but also to ensure that safety precautions are taken to avoid contamination of laboratory personnel. Serological tests (detection of antibodies in the serum of the patients) are available and widely used. Cross reactivity with Brucella can confuse interpretation of the results, so diagnosis should not rely only on serology. Molecular methods such as PCR are available in reference laboratories.
Prevention[edit]
There are no safe, available, approved vaccines against tularemia. However, vaccination research and development continues, with live attenuated vaccines being the most thoroughly researched and most likely candidate for approval.[23] Sub-unit vaccine candidates, such as killed-whole cell vaccines, are also under investigation, however research has not reached a state of public use.[23]
Optimal preventative practices include limiting direct exposure when handling potentially infected animals by wearing gloves and face masks (importantly when skinning deceased animals).[24]
Treatment[edit]
If infection occurs or is suspected, treatment is generally with the antibiotics streptomycin or gentamicin.[24] Doxycycline was previously used.[25] Gentamicin may be easier to obtain than streptomycin.[25] There is also tentative evidence to support the use of quinolone antibiotics.[25]
History[edit]
The tularemia bacterium was first isolated by G.W. McCoy of the United States Public Health Service plague lab and reported in 1912.[41][42] Scientists determined tularemia could be dangerous to humans; a human being may catch the infection after contacting an infected animal. The ailment soon became associated with hunters, cooks and agricultural workers.[43]
The Centers for Disease Control and Prevention (CDC) regard F. tularensis as a viable biological warfare agent, and it has been included in the biological warfare programs of the United States, Soviet Union and Japan at various times.[44] A former Soviet biological weapons scientist, Ken Alibek, has alleged that an outbreak of tularemia among German soldiers shortly before the Battle of Stalingrad was due to the release of F. tularensis by Soviet forces. Others who have studied the pathogen "propose that an outbreak resulting from natural causes is more likely".[45][46] In the United States, practical research into using rabbit fever as a biological warfare agent took place in 1954 at Pine Bluff Arsenal, Arkansas, an extension of the Fort Detrick program.[47] It was viewed as an attractive agent because:
The Schu S4 strain was standardized as "Agent UL" for use in the United States M143 bursting spherical bomblet. It was a lethal biological warfare agent with an anticipated fatality rate of 40–60%. The rate-of-action was around three days, with a duration-of-action of one to three weeks (treated) and two to three months (untreated), with frequent relapses. UL was streptomycin resistant. The aerobiological stability of UL was a major concern, being sensitive to sunlight, and losing virulence over time after release. When the 425 strain was standardized as "agent JT" (an incapacitant rather than lethal agent), the Schu S4 strain's symbol was changed again to SR.
Both wet and dry types of F. tularensis (identified by the codes TT and ZZ) were examined during the "Red Cloud" tests, which took place from November 1966 to February 1967 in the Tanana Valley, Alaska.[48]
Other animals[edit]
Cats and dogs can acquire the disease from the bite of a tick or flea that has fed on an infected host, such as a rabbit or rodent. For treatment of infected cats, antibiotics are the preferred treatment, including tetracycline, chloramphenicol or streptomycin. Long treatment courses may be necessary as relapses are common.[49]