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February 2016

Horse: Liver: Granuloma, multifocal, chronic
(parasitic granulomas consistent with equine cystic echinococcosis)

01_16_C

History

Horse, Connemara pony, male, 17 years

 

Diagnosis

Liver: Granuloma, multifocal, chronic (parasitic granulomas consistent with equine cystic echinococcosis)

 

Description

A well-demarcated, grey-white, fluctuating mass of 5 cm in diameter was present on the serosal surface of the liver. Additionally, smaller granulomas with up to 1 cm in diameter were visible in the superficial parenchyma partially protruding from the surface. The cysts were filled with clear, amber-colored liquid containing particles of less than 1mm in diameter (hydatid sand).

 

Comments

The horse was euthanized on account of chronic colitis and an oromaxillary sinus fistula.

 

Necropsy revealed several thick-walled grey-white focal cysts of maximal 5 cm in diameter on the visceral surface of the liver and the lung.

Histopathology revealed a tri-layered appearance of the cysts with an outer connective tissue capsule followed by a hyaline acellular and an inner germinal membrane. The cysts contained few free protoscolices consistent with Echinococcus spp. characterized by a 5 µm thick tegument enclosing spongy parenchyma with multifocal calcareous corpuscles, a sucker and a rostellum armed with birefringent hooks.

 

Echincococcus equinus infections are rare in Europe and mostly an incidental finding at postmortem examination. Echinoccocus equinus is a cestode with a 2-host life cycle, with carnivores (mostly canids) as definite hosts and equines (mostly horses) as intermediate hosts. In the intermediate hosts hydatid cysts mainly develop in the liver and the lung. To date Echinococcus equinus infections are not reported in humans.

 

Picture and authored by Sophie Merz, Department of Veterinary Pathology, Freie Universität Berlin, Germany