Zoonotic & Environmental Bacterial Infections

Four zoonotic/environmental bacterial infections with no dedicated existing page. See also lyme disease, tick bite and rabies/other lyssaviruses for other tick-borne/zoonotic topics.

Leptospirosis

A zoonosis (Leptospira spp.; reservoirs include rats, pigs, cattle, horses, dogs) transmitted when infected animal urine contacts skin abrasions or mucous membranes — an occupational infection of farmers (especially dairy), abattoir/meat workers, and those in wet environments.

Murtagh triad — abrupt fever + headache + conjunctival suffusion.

Severe disease (Weil’s disease) causes jaundice, renal failure and bleeding.

• Diagnosis: serology (MAT) or culture/PCR.
• Treatment: doxycycline (7 days) for mild disease; IV benzylpenicillin/ ceftriaxone for severe.

Brucellosis

A zoonosis — in Australia mainly from feral pigs (hunters); overseas from unpasteurised dairy/livestock. Rare in Australia (Queensland into parts of NSW/NT); endemic in the Middle East and southern Europe. Occasional person-to-person transmission.

• Presentation: a prolonged febrile illness (weeks) — undulant fever, sweats, malaise, arthralgia.
• Complications: endocarditis (the main cause of death), neurobrucellosis, and osteoarticular disease (e.g. sacroiliitis, spondylitis).
• Treatment: doxycycline for 6 weeks + gentamicin (IV) for ~1 week (rifampicin is an alternative companion drug).

Plague

Caused by Yersinia pestis (“the Black Death”). Rare (~1000–3000 cases/year worldwide, e.g. Madagascar, DRC, western USA). Transmitted by fleas that have bitten infected rodents; person-to-person spread occurs (notably pneumonic).

Forms:

• Bubonic — painful, suppurative inguinal/axillary lymphadenitis (buboes).
• Pneumonic — flu-like illness with haemoptysis; highly transmissible and rapidly fatal.
• Septicaemic — sudden high fever, myalgia, abdominal pain, diarrhoea, then black patches of skin from subcutaneous haemorrhage.

High mortality untreated; treat with aminoglycosides (gentamicin/streptomycin) or doxycycline/fluoroquinolone, with isolation for pneumonic plague. A notifiable disease of international significance.

Melioidosis

Infection with Burkholderia pseudomallei, from soil and surface water in northern Australia and the Asia-Pacific, classically acquired through an open wound (e.g. wading in rice paddies) or by inhalation, especially in the wet season. May present years after exposure. Risk factors: diabetes, hazardous alcohol use, chronic lung/kidney disease.

• Presentation: most commonly pneumonia, but can form an abscess in any organ (skin, liver, spleen, prostate) and cause sepsis.
• Diagnosis: culture of blood and infected sites (notify the lab — it’s a hazardous organism).
• Treatment: an intensive IV phase (ceftazidime or meropenem) followed by prolonged oral eradication (co-trimoxazole).