The pathology of bronchointerstitial pneumonia in young foals associated with the first outbreak of equine influenza in Australia

Abstract

Given the findings in this outbreak, and a previous outbreak in the UK in 1965 involving a similarly naive population, veterinary clinicians and pathologists should be aware that EIV can cause fatal bronchointerstitial pneumonia in young foals that do not have maternal immunity. The lesions did not differ from those previously reported in foals of various ages with bronchointerstitial pneumonia of other or undefined causes, indicating that this is most likely a stereotypical response to a variety of insults. Therefore, tissue specimens should be obtained from cases of pneumonia in young foals for virological and bacteriological testing.

Time-related Pathological Changes in Horses Experimentally Inoculated with Equine Influenza A Virus

“…EI is usually curable with symptomatic treatment. However, horses infected with EIV may develop fatal secondary bacterial pneumonia [2, 13, 18, 19]. Streptococcus equi subsp.…”

“…Streptococcus equi subsp. zooepidemicus (S. zooepidemicus) is one of the most common potential pathogens of secondary bacterial pneumonia following EI [8, 13, 15, 25]. …”

“…Few horses had severe clinical manifestations, and the epidemic was contained within a fairly limited area, probably because of mandatory vaccination and/or restriction of horse movements [12, 24]. During the EI outbreak in the Australian horse population in 2007, some deaths of young foals and mature horses occurred [2, 13]. These fatally affected animals had extensive pulmonary lesions [2, 13].…”

“…During the EI outbreak in the Australian horse population in 2007, some deaths of young foals and mature horses occurred [2, 13]. These fatally affected animals had extensive pulmonary lesions [2, 13]. However, the pathological lesions in these cases consisted mainly of suppurative bronchopneumonia resulting from secondary bacterial infection, which is considered to be only part of the pathological process of EI [19].…”

“…Previous studies have approached EI from the perspective of clinical virology or clinical microbiology, but have not been supported by histopathology. Histopathological reports of EI are currently limited to those of cases in which horses have died from the secondary bacterial pneumonia that follows EIV infection [9, 13]. The gross and histologic lesions of uncomplicated EI have not been adequately described, as horses infected with EIV rarely die in the acute stage [4].…”