Phys · infectious
Zoonotic and Vector-Borne Infections
Also known as Q fever · Coxiella burnetii · query fever · leptospirosis · Weil disease · scrub typhus · Orientia tsutsugamushi · Queensland tick typhus · Rickettsia australis · spotted fever · brucellosis · undulant fever · cat-scratch disease · Bartonella henselae · bacillary angiomatosis · toxoplasmosis · Toxoplasma gondii · cerebral toxoplasmosis · hantavirus · hantavirus pulmonary syndrome · Lyme disease · Borrelia burgdorferi · erythema migrans · culture-negative endocarditis · Q-VAX vaccine
Consultant-physician-depth guide to the zoonotic and vector-borne infections relevant to ANZ and global practice — Q fever (Coxiella burnetii, phase I and II serology, doxycycline plus hydroxychloroquine for chronic endocarditis, Q-VAX vaccine), leptospirosis (biphasic illness, Weil disease, conjunctival suffusion, MAT serology, doxycycline and ceftriaxone), scrub typhus (eschar, Orientia tsutsugamushi, doxycycline, endemic in northern Australia), Queensland tick typhus (Rickettsia australis), brucellosis (undulant fever, doxycycline plus rifampicin for 6 weeks), Bartonella (cat-scratch disease, bacillary angiomatosis, culture-negative endocarditis), toxoplasmosis (cerebral toxoplasmosis in HIV, pyrimethamine-sulfadiazine-folinic acid), hantavirus (HFRS, pulmonary syndrome), Lyme disease (NOT endemic in Australia, imported only), and the ANZ-specific arboviruses — structured for FRACP DWE and DCE preparation.
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Red flags
- Any patient with a prosthetic valve and culture-negative endocarditis has Q fever (Coxiella burnetii) until excluded — send phase I and phase II serology, because the organism will not grow on routine blood cultures and is a major modified Duke criterion
- An eschar with fever and headache in a traveller or resident from northern Australia or the Asia-Pacific is scrub typhus or another rickettsial disease — start doxycycline empirically; do not wait for serology, because untreated severe scrub typhus has a mortality up to 30 per cent
- Fever with conjunctival suffusion, severe myalgia and jaundice after freshwater or animal-urine exposure is leptospirosis (Weil disease) — start IV ceftriaxone immediately; the severe pulmonary haemorrhage form can be rapidly fatal
- An HIV-positive patient with CD4 below 100 and multiple ring-enhancing brain lesions has cerebral toxoplasmosis until proven otherwise — start pyrimethamine plus sulfadiazine plus folinic acid; untreated mortality approaches 100 per cent
- Fever with thrombocytopenia, rising creatinine and a prodrome of myalgia and abdominal pain after rodent exposure is hantavirus — recognise the prodrome early, because the cardiopulmonary phase can progress to non-cardiogenic pulmonary oedema within hours
- Any abattoir worker, veterinarian or farmer with a flu-like illness and hepatitis has Q fever until excluded — send serology, and screen for endocarditis if there is a prosthetic or abnormal native valve
- Brucellosis treated with a single antibiotic has a relapse rate above 30 per cent — always use combination therapy (doxycycline plus rifampicin or streptomycin) for at least 6 weeks
Zoonotic and Vector-Borne Infections
[1]The one-minute consultant answer
A zoonotic infection is suspected when the exposure history points to an animal or vector source — the occupation (abattoir worker, farmer, veterinarian), the recreation (hunting, freshwater swimming, bushwalking in northern Australia), the animal contact (cats, sheep, cattle, goats, rodents), the vector (tick, mite, flea), or the dietary history (unpasteurised dairy, undercooked meat). The single most important diagnostic step is therefore not the blood test but the exposure history — the registrar who takes it well will diagnose a zoonosis the laboratory has never heard of, while the registrar who does not will miss it. Once the exposure is identified, match it to the clinical syndrome — the eschar (scrub typhus, tick typhus), the undulant fever (brucellosis), the culture-negative endocarditis (Q fever, Bartonella), the biphasic illness with jaundice (leptospirosis), the ring-enhancing brain lesions in HIV (toxoplasmosis), the erythema migrans in a returned traveller (Lyme disease). [1]
The treatment decisions that examiners test are few and must be automatic. Acute Q fever gets doxycycline for 14 days; chronic Q fever endocarditis gets doxycycline plus hydroxychloroquine for at least 18 months — the hydroxychloroquine alkalinises the phagolysosome, restoring doxycycline bactericidal activity [1]. Leptospirosis gets doxycycline for mild disease and IV ceftriaxone for severe (Weil) disease [3]. Scrub typhus gets doxycycline, started empirically before serology returns; severe scrub typhus gets combination IV doxycycline plus azithromycin [4]. Brucellosis gets doxycycline plus rifampicin (or streptomycin) for at least 6 weeks — never monotherapy [6]. Cerebral toxoplasmosis gets pyrimethamine plus sulfadiazine plus folinic acid — not folic acid [8]. Lyme disease gets doxycycline or amoxicillin for erythema migrans, ceftriaxone for neuroborreliosis [9].
The ANZ-specific principle that examiners love: Lyme disease is NOT endemic in Australia. All locally-diagnosed "Lyme disease" in Australia is either imported (from the northern hemisphere) or mislabelled. A patient with a rash after a tick bite in Australia has a rickettsial disease (Rickettsia australis, Queensland tick typhus), not Lyme. This is a high-yield discriminator that separates the informed candidate from the one who has not studied the local epidemiology. [1]
References9ShowHide
- [1]Raoult D, Houpikian P, Tissot Dupont H, Riss JM, Arditi-Djiane J, Brouqui P Treatment of Q fever endocarditis: comparison of 2 regimens containing doxycycline and ofloxacin or hydroxychloroquine Arch Intern Med, 1999.PMID 9927100
- [2]Ackland JR, Worswick DA, Marmion BP Vaccine prophylaxis of Q fever. A follow-up study of the efficacy of Q-Vax (CSL) 1985-1990. Med J Aust, 1994.PMID 8202006
- [3]Ji Z, Jian M, Su X, et al. Efficacy and safety of antibiotics for treatment of leptospirosis: a systematic review and network meta-analysis Syst Rev, 2024.PMID 38627798
- [4]Varghese GM, Dayanand D, Gunasekaran K, et al. Intravenous Doxycycline, Azithromycin, or Both for Severe Scrub Typhus N Engl J Med, 2023.PMID 36856615
- [6]Ariza J, Gudiol F, Pallares R, et al. Treatment of human brucellosis with doxycycline plus rifampin or doxycycline plus streptomycin. A randomized, double-blind study. Ann Intern Med, 1992.PMID 1596044
- [7]Prosty C, Hanula R, Levin Y, et al. Revisiting the Evidence Base for Modern-Day Practice of the Treatment of Toxoplasmic Encephalitis: A Systematic Review and Meta-Analysis Clin Infect Dis, 2023.PMID 35944134
- [8]Leport C, Raffi F, Matheron S, et al. Treatment of central nervous system toxoplasmosis with pyrimethamine/sulfadiazine combination in 35 patients with the acquired immunodeficiency syndrome. Efficacy of long-term continuous therapy Am J Med, 1988.PMID 3337134
- [9]Lantos PM, Rumbaugh J, Bockenstedt LK, et al. Clinical Practice Guidelines by the Infectious Diseases Society of America (IDSA), American Academy of Neurology (AAN), and American College of Rheumatology (ACR): 2020 Guidelines for the Prevention, Diagnosis and Treatment of Lyme Disease. Clin Infect Dis, 2021.PMID 33483734
- [10]Bond KA, Franklin L, Sutton B, et al. Q-Vax Q fever vaccine failures, Victoria, Australia 1994-2013 Vaccine, 2017.PMID 29132996