A lung infection caused by the fungus Aspergillus should be suspected whenever a severe respiratory syndrome occurs after gastrointestinal tract disease in horses, particularly when antimicrobials prove ineffective, according to researchers.
Researchers in Italy made the observation in a case report detailing a fatal case of equine pulmonary aspergillosis in a foal. It is a rare deep fungal infection often spread through the blood after gastrointestinal tract disease.
The foal in question, a 10-month-old Quarter Horse colt, spontaneously died after showing diarrhea and respiratory distress, Jasmine Hattab and her fellow researchers reported in the journal Pathogens.
Investigations after his death allowed researchers to diagnose pulmonary aspergillosis, which likely developed after a bout of necrotic inflammatory bowel disease.
Aspergillus species are common around the globe. The filamentous fungi thrive in the soil and occasionally infect animals as opportunistic pathogens.
As a general rule, horses would have to be immune-suppressed or have some other debilitating condition to make them prone to fungal diseases, including aspergillosis.
Horses usually become infected through inhalation of fungal spores, but it can also spread through the blood after the gut wall is compromised by acute enteritis.
Aspergillus species can synthesize oxalic acid, which reacts with blood and tissue calcium to precipitate as oxalate crystals.
Aspergillus fumigatus is the most commonly documented cause of equine pulmonary aspergillosis, although the identification of the causative agent often remains at the genus level.
The foal at the center of the study was kept in a single box provided with an external paddock and was fed with hay and flaked feed.
The foal suddenly went down, did not eat, and was breathing rapidly. Within 24 hours, the clinical picture severely worsened, with a fever (42°C), shortness of breath, a fast heart rate, and profuse watery diarrhea.
The foal was given intravenous fluids, vitamin B complex and diosmectite, the latter in a bid to ease the diarrhea. However, the clinical signs further worsened, and the foal spontaneously died 48 hours after the onset of the disease.
A wide range of tissue samples were taken for examination, with lesions identified in the large intestine and the lungs. The mucosa of the cecum and colon appeared necrotic, with abundant watery content in the bowel. The intestinal lining was diffusely necrotic.
Both lungs appeared severely hyperemic — having excess blood in the vessels — and were swollen with fluid.
Microscopically, pulmonary nodules appeared engorged with blood, while the alveolar walls were thickened and congested. Areas of necrosis and bleeding were also seen.
A huge number of branching fungal filaments, resembling Aspergillus species, were detected in the lungs.
Biomolecular studies identified Aspergillus section Fumigati strain as the cause.
The kidneys were also found to be severely infected, with extensive nephrosis observed. Translucent and fan-shaped crystals filled almost all renal tubules. They were identified as calcium oxalates.
Discussing the case, the authors acknowledged that equine pulmonary aspergillosis is widely recognized as a rare disease condition.
In the current case, the inflammatory gut problem likely disrupted the mucosal barrier of the large intestine and allowed the fungi to spread via the blood.
The presence of lesions in both lungs, along with the detection of hyphae in the blood vessels, further supports this hypothesis.
They believed that the oxalate nephrosis occurred as a secondary event after fungal-induced pneumonia.
They speculated that the oxalates, produced in the lungs during the Aspergillus infection, can reach the kidneys through the bloodstream, accumulating in the renal tubules.
“As far as the horse is concerned, the presence of oxalate crystals has been reported only in two cases of aspergillosis.”
They concluded: “The present case report supports that equine pulmonary aspergillosis should be suspected whenever a severe respiratory syndrome occurs after a gastrointestinal tract disease, particularly when antimicrobials prove to be ineffective.”
Oxalate nephrosis can represent a severe, clinically relevant consequence of equine pulmonary aspergillosis — as occasionally observed in human medicine — thus likely contributing to the fatal outcome of the disease, they said.
The study team comprised Hattab, Antonella Vulcano, Silvia D’Arezzo, Fabiana Verni, Pietro Giorgio Tiscar, Giovanni Lanteri, Emil Gjurcevic, Umberto Tosi and Giuseppe Marruchella, variously affiliated with a range of Italian institutions, including the University of Teramo.
Hattab, J.; Vulcano, A.; D’Arezzo, S.; Verni, F.; Tiscar, P.G.; Lanteri, G.; Gjurcevic, E.; Tosi, U.; Marruchella, G. Aspergillus Section Fumigati Pneumonia and Oxalate Nephrosis in a Foal. Pathogens 2021, 10, 1087. https://doi.org/10.3390/pathogens10091087