Infection of humans and horses by a newly described morbillivirus

OBJECTIVE: To describe the clinical and epidemiological features of an outbreak of a viral infection affecting humans and horses. SETTING: Stables in Hendra, a suburb of Brisbane. SUBJECTS: Affected horses and humans, and at-risk human contacts. RESULTS: A pregnant mare died two days after arrival from a paddock elsewhere in Brisbane. Eight to 11 days later, illness (depression, anorexia, fever, dyspnoea, ataxia, tachycardia, tachypnoea and nasal discharge) was reported among 17 other horses from the same or an adjoining stable. Fourteen horses died or were put down. Five and six days after the index mare's death, a stable-hand and then a horse-trainer, both of whom had had close contact with the sick mare's mucous secretions, developed influenza-like illnesses. The stable-hand recovered but the trainer developed pneumonitis, respiratory failure, renal failure and arterial thrombosis, and died from a cardiac arrest seven days after admission to hospital. A morbillivirus cultured from his kidney was identical to one isolated from the lungs of five affected horses. The two affected humans and eight other horses were seropositive for the infection, which was reproduced in healthy horses following challenge by spleen/lung homogenates from infected horses. There was no serological evidence of infection in 157 humans who had had contact with the stables or the sick horses or humans. CONCLUSIONS: A previously undescribed morbillivirus infected a probable 21 horses and two humans; one human and 14 horses died. That no further cases were detected among humans suggests that the virus was of low infectivity. The source of infection remains undetermined.