The abdominal ultrasound of the horse showed the presence of an abundant amount of fluid and thickening of the parietal peritoneum where rounded formations adhered in clusters. Passantino et al. https://doi.org/10.3390/ani12192
A rare case of mesothelioma, a form of cancer linked to asbestos exposure in humans and dogs, has been reported in an older horse in Italy.
The case in a 22-year-old Quarter Horse gelding in the Lazio region is described in the September issue of the journal Animals.
Mesothelioma develops in the mesothelium, the thin layer of tissue that covers many internal organs. The most common area affected is the lining of the lungs and chest wall. It can also affect the abdominal lining and, rarely, the sac around the heart.
In humans, more than 80% of cases are caused by asbestos exposure, with greater levels of exposure creating a higher risk.
Mesotheliomas can affect different species, including dogs, cats, cattle, sheep, goats, and horses.
The onset in horses is very rare, Giuseppe Passantino and his fellow researchers noted in their case report.
Since 1976, there have been around 11 reports of mesothelioma in horses, located typically in the pericardium, the pleural cavity or peritoneal cavity.
Most reported cases have involved mares aged 2 to 27, with a higher incidence in adults and older horses. There is no obvious breed predisposition. In most cases of equine mesothelioma, the diagnosis is made after death, either at the slaughterhouse or during a necropsy.
The chestnut gelding at the centre of the case report was kept in a paddock and used in equestrian tourist activities. The owner said the horse had suffered no major ill health during his life.
The horse, who had lost condition, was taken to a veterinary clinic in Rome because of colic-like pain and sensory depression. His heart rate was rapid and his breathing elevated. His mucous membranes were congested and his hematocrit level was elevated. Intestinal sounds were muted.
An abdominal ultrasound showed excessive fluid build-up and rounded abdominal masses adhering to the peritoneum.
Despite treatment over five days, the condition of the horse worsened and the decision was made to euthanise him. A post-mortem examination two hours later revealed a large quantity of fluid around the abdomen and chest.
The examination revealed numerous nodular masses on the peritoneum, omentum, lungs, heart, and mediastinum. They were up to 4cm in size, diffuse, whitish and red, with a fatty appearance, and arranged in clusters.
A diagnosis of epithelioid mesothelioma was made through microscopic examination and confirmed with immunohistochemistry.
The authors hypothesized that the primary tumor most likely originated from the peritoneum and had spread to the local lymph nodes and chest cavity. However, a multicenter origin of the tumor cannot be completely ruled out, they said.
The cause of mesotheliomas in horses is unknown, they noted, while in humans and dogs it has been reported that exposure to asbestos dust induces its onset. The cause of the cancer in the case report was most likely environmental in nature, they said.
In fact, the horse lived in an area with a very high incidence rate of human mesothelioma, the authors said. “Another case came from the same area, in which both the horse and the owner were suffering from lymphoma.”
Because of the environmental origin of this form of cancer, it would be prudent to monitor other horses in the same area in order to evaluate the presence of mesothelioma, they said. It would also be interesting to provide useful tools for an early diagnosis of the disease using similar diagnostic methods to those used in humans, and to propose a cause for this cancer in horses that, to date, is still unknown.
The case-report team comprised Passantino, Antonella Tinelli and Nicola Zizzo, with the University of Bari Aldo Moro; Emilio Sassi and Ilaria Filippi, who are both independent researchers; and Valerio Serata, with Equine Practice SRL in Campagnano di Roma.
Passantino, G.; Sassi, E.; Filippi, I.; Serata, V.; Tinelli, A.; Zizzo, N. Thoracic and Abdominal Mesothelioma in an Older Horse in Lazio Region. Animals 2022, 12, 2560. https://doi.org/10.3390/ani12192560
The study, published under a Creative Commons License, can be read here.