Tularemia

The Tularemia is a disease of wild mammals, caused by Francisella tularensis, most often between 30 and 71º north latitude.

It occurs by sporadic outbreaks, and affects all ages and races.

Causes of tularemia

It is produced by Francisella tularensis, a short, pleomorphic coccobacillus that can show bipolar staining, although it manifests itself more frequently as a gram-negative bacillus that does not form spores.

It is transmitted to man by:

• arthropod bites
• direct contact with infected animals
• inhalation of aerosols
• ingestion of contaminated food or water

You need very low infective doses of less than 100 microorganisms.

Most of the time it is acquired by contact with an infected rabbit or tick. Other mammals such as squirrels, muskrats, badgers, and deer can also become infected. Likewise, the bite or scratch of a domestic dog or cat has been implicated, after having ingested an infected rodent.

The usual vector is the tick or horsefly.

It must be considered that the tick can also act as a reservoir, by transmitting it to its offspring by transovarian route.

Francisella tularensis infects the reticuloendothelial organs and produces caseating granulomas and abscesses, which confer long-lasting cell-like immunity.

It is not transmitted from person to person.

Symptoms of turalemia

After an incubation period of 2-5 days, fever , malaise and chills appear.

There are different clinical forms depending on the entrance door:

Ulceroglandular tularemia

It represents 70-80% of the cases of tularemia. It originates by inoculation through the skin. A local papule is produced that becomes necrotic and ulcerated. Regional lymph nodes appear swollen and painful.

Glandular tularemia

It represents 5-10% of tularemia cases. The clinical picture is similar to the previous one except for ulceration.

Oculoglandular tularemia

It represents 1-2% of tularemia cases. It is caused by touching the conjunctiva with the infected finger or when a droplet reaches the eye. Painful purulent conjunctivitis appears, causing yellowish granulomatous lesions on the eyelids and preauricular lymphadenopathy.

Typhoid tularemia

It represents 5-15% of tularemia cases. It originates by direct inoculation, by the digestive or respiratory route. The clinic resembles typhoid fever , with abdominal manifestations and prolonged fever.

Pulmonary tularemia

It originates by inhalation and seeding after bacteremic spread in patients with any of the other clinical forms of tularemia.

oropharyngeal tularemia

It causes a clinical picture of acute or membranous pharyngotonsillitis, with fever and cervical lymphadenopathy.

How is it diagnosed?

Because it is a rare disease and that Francisella tularensis has special growth requirements, it is necessary to inform the laboratory of the suspicion of it.

The culture of this microorganism requires blood agar with glucose and cysteine ​​or cystine, and thioglycollate broth at 37ºC in aerobiosis.

At 24-48 hours, the colonies are opaque, smooth, and small.

Culture media with penicillin and polymyxin B can be used. Thayer-Martin’s medium also seems useful.

Identification of Francisella tularensis can be done by:

• morphological characteristics: pleomorphic gram negative coccobacillus.
• biological properties: immobile, ferments (glucose, maltose and mannose) and originates.
• sulfhydric in media with cysteine.
• immunofluorescence techniques.
• agglutination techniques against specific sera.

Antibodies appear after one week and positive titers are found in 50-70% of cases after two weeks.

Titles of 1/80 or 1/160 are significant.
A titer increase of at least four times more occurs when two serum extractions are performed approximately two weeks apart.

Remember that antibodies also react with Brucella, and sera must undergo an agglutinin absorption process.

Another form of diagnosis is the skin test, since Francisella is a facultative intracellular parasite of the reticuloendothelial system, and it causes a state of cell-mediated immunity.

Treatment of turalemia

The treatment of choice is streptomycin at a dose of 15-20 mg / kg / day intramuscularly or gentamicin at a dose of 1.5 mg / kg / 8 hours intravenously, for a period of 14 days.

Chloramphenicol and tetracyclines have been proposed as alternatives, but present a higher number of relapses.

How can I avoid it?

The use of rubber gloves and eye protection is important when handling potentially infected wild mammals.

Ticks must be removed quickly.

There is an attenuated vaccine administered by scarification, for laboratory workers and patients who cannot avoid contact with infected animals, which confer partial protection.

Preventive measures thus include:

• health education
• passive protection when handling animals
• fight arthropods
• use of repellers
• vaccination

We must go to the doctor when the symptoms already described appear.

If we work with potentially contagious animals, it is advisable to consult a doctor about the vaccine, to avoid contagion.