Tularaemia is due to infection by Francisella tularensis, a Gram-negative organism. It is primarily a zoonosis, affecting mainly rodents, including rabbits and squirrels. Vectors are ticks, flies and mosquitoes. Humans are infected by handling infected animals or from vector bites. The microorganisms enter through the skin or through minor abrasions in the mouth or conjunctivae. Occasionally infection occurs from contaminated water or from eating uncooked meat. The disease occurs worldwide and is frequently seen in the USA, particularly in hunters and butchers.
The incubation period of 2-7 days is followed by a generalized illness. A number of clinical syndromes can be seen:
THE ULCEROGLANDULAR FORM is the commonest. A papule occurs at the site of inoculation. This ulcerates and is followed by tender, suppurative lymphadenopathy. Infected material entering the eye is followed by a purulent conjunctivitis with periauricular lymphadenopathy.
PNEUMONIC FORMS present with cough, chest pain and eventually a pneumonia, sometimes accompanied by a pericarditis.
THE SEPTICAEMIC FORM presents with the sudden onset of a fever, myalgia, headache and shock.
Diagnosis is by culture of the organism or by a rising titre seen on a bacterial agglutination test.
Treatment is with streptomycin or more usually gentamicin. The patient should be isolated.
In endemic areas all wild animals should be handled using gloves. Infected meat and water should be adequately cooked. A vaccine is available for laboratory staff handling possibly infected animals.
Glanders is caused by a Gram-negative bacillus, Pseudomonas mallei. It affects mainly horses but can very rarely be transmitted to humans, mainly horse handlers. The disease is acquired by inhalation or inoculation of nfected material. In the acute state, the patient is toxic with a high fever and delirium. There is an ulceration of the upper respiratory tract with eventual pneumonia, empyema and lung abscess. Septicaemia develops. Treatment is with i.v. broad spectrum antibiotics.
Melioidosis is due to the Gram-negative bacillus, Pseudomonas pseudo mallei, which is a soil saprophyte. It infects humans (particularly diabetics or traumatized patients) by penetrating through skin abrasions, occasionally byinhalation, or via ingestion of contaminated water. It is found worldwide, but occurs mainly in South East Asia. Septicaemia with abscesses in the lung, kidney, liver and spleen may occur. The eNS may be involved. The prognosis is poor. A chronic form, usually presenting with an unresolved pneumonia, also occurs. Diagnosis is by culture of the organism. An indirect haemagglutination test is positive after 1 week.
The patient should be barrier-nursed and treated with ceftazidime.
Pasteurelloses are infections primarily of animals. Three species are known to infect humans, the commonest being Pasteurella multocida, which is also the most virulent. All these organisms are commensal in the nasopharynxand gastrointestinal tract of a number of dom-estic and wild mammals. T ransmission to humans may occur through a bite or scratch.
Focal soft tissue infection with marked erythema, severe tenderness and regional lymphadenopathy may be present. These organisms are also responsible for chronic respiratory infections, bacteraemia, and brain and renal abscesses.
Penicillin is the drug of choice and should be given parenterally as benzylpenicillin 1-2 g every 4 hours. BARTONELLOSIS (CARRION’S DISEASE) This is caused by Bartonella bacilliformis, a Gram-negative bacillus. It is mainly restricted to the habitat of its main vector, sandfly, in the river valleys of the Andes mountains at an altitude of 500-3000 m. Two to six weeks following the bite, the patient develops ‘oroya fever’ with myalgia, arthralgia, severe headache and confusion followed by a haemolytic anaemia. Four to five weeks later reddish-purple haemangiomatous nodules develop and persist for 3-4 months. Superinfection can occur particularly with Salmonella.
Diagnosis is by finding bacilli in erythrocytes or blood culture.
Treatment is with chloramphenicol, tetracycline or penicillin.
This is caused by the fastidious Legionella pneumophila; a weakly Gram-negative, catalase-positive bacillus.
Bacteroides is an obligate anaerobic, Gram-negative bacillus. B. fragilis is the most important anaerobic human pathogen and is a normal commensal in the human large gut. It does not produce an endotoxin and because of its polysaccharide capsule it resists phagocytosis. B. fragilis also produces heparinase, which may be involved in the development of thrombophlebitis, and l3-lactamases, which inhibit the action of penicillin. It is not a highly invasive organism and grows best in necrotic tissues.
eventy-five per cent of all intra-abdominal infections, particularly postoperative infections, are caused by anaerobes. Bacteroides is a frequent cause of hepatic, subhepatic, pelvic and splenic abscesses. The pus has a characteristic putrid smell. Bacteroides also causes pelvic infections and may result in endometritis, Bartholin’s abscess and pelvic peritonitis. Bacteraemia and Fournier’s gangrene are also caused by B. fragilis.
This depends on strict anaerobic culture with special media. Gas-liquid chromatography has been used to detect the volatile fatty acids produced by anaerobic bacteria.
Surgery is usually required as well as chemotherapy. Metronidazole (1-2 g daily by mouth or 1 g 8-hourly by rectum) is the drug of choice; it is also used prophylactically in colorectal surgery, with a dramatic reduction in postoperative infections.