European Society of Toxicologic Pathology (ESTP)
    European Society of Toxicologic Pathology
Guess What! - ESTP Case 12

Animal / species: Macaca fascicularis, sive cynomolgus monkey, purpose bred animal imported from China.
Sex / age / weight : Female animal approx. 4 years of age, body weight approx. 4 kg.
Use in toxicology: Animal in a standard 4-week toxicology-study, low dose group, no treatment-related macroscopical findings.
Spontaneous finding: Cystic mass, approx. 2 cm in diameter in the lung.
Slide: Section from the mass in the lung, standard paraffin embedding, H&E stained slides.

Click on the images below for a larger view.
Case 12, Fig. 1
Fig. 1: Cystic mass in the lung, H&E, x40
Case 12, Fig. 2
Fig. 2: Cystic mass in the lung, H&E, x20
Case 12, Fig. 3
Fig. 3: Cystic mass in the lung, H&E, x10
Case 12, Fig. 4
Fig. 4: Cystic mass in the lung, H&E, x4

Morphologic Description

Case # 12 showed the histopathological appearance of a single unilocular cyst of approximately 2 cm in diameter in the lung of a female purpose bred cynomolgus monkey. The animal had been imported from a breeder in China, was approximately 4 years of age and had a body-weight of about 4 kg.

Proposed Diagnosis
Cystic Echinococcosis, caused by Echinococcus granulosus

Unilocular hydatid cyst, characterized by the thick outer laminated layer with a thin layer of calcareous corpuscles at the inner surface. Inside the cyst numerous protoscolices which are grouped in brood capsules. Besides inflammation and atelektasis, the surrounding adjacent lung tissue forms a fibrous periparasitic host tissue (pericyst), which encompasses the parasitic endocyst.

Hydatid cysts are caused by Echinococcus spp. Due to the morphology of this unilocular hydatid, Echinococcus granulosus is considered the causative agent.


All contributors (14) diagnosed a focal parasitic granuloma. 9 out of 14 contributors further specified Echinococcus as the underlying infectious agent. There were three participants suggesting E. granulosus and two suggesting E. multilocularis. Echinococcus spp. belong to the family of Taeniidae within the class of Cestoda. Echinococcus granulosus is the causative agent of cystic echinococcosis, while E. multiolocularis causes alveolar echinococcosis. As infestations of both parasites spp. have been described in cynomolgus monkeys, the differential diagnosis can be made only by morphological criteria or by immunohistochemistry using specific antibodies against E. multilocularis or E. granulosus. However, multilocular cysts with invasive growth have been a constant feature of alveolar echinococcosis and the animals in most of the recently reported cases have been infected in Europe. Our case shows unilocular expansive growing cysts and the animal surely has been infected already at the breeder in China.

Echinococcus infestations are infrequently seen in our cynomolgus monkeys. The – sometimes huge – hydatids are predominantly located in the liver and greater omentum (Fig. 5). However, in most cases the hydatids have been sterile: Inside the hyaline laminated layer, only large amounts of proteinaceous clear fluid, but no active germinal layers, brood capsules or protoscolices could be demonstrated.

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Case 12, Fig. 5
Fig. 5: Huge hydatid in the liver (1) with gallbladder (2), inside the fibrous host tissue parasitic cyst with clear, proteinaceous jelly-like fluid (3)


  • Bacciarini LN, Gottstein B, Pagan O, Rehmann P, Grone A (2004) Hepatic alveolar echinococcosis in cynomolgus monkeys (Macaca fascicularis). Vet Pathol 41: 229-234
  • Blankenburg A (2004) Untersuchungen zur alveolären Echinokokkose bei Bartaffen (macaca silenus) Vet. med. Diss., Hannover
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  • Helbig M, Frosch P, Kern P, Frosch M (1993) Serological differentiation between cystic and alveolar echinococcosis by use of recombinant larval antigens. J Clin Microbiol 31: 3211-3215
  • Myers BJ (1972) Echinococcosis, Coenurosis, Cysticercosis Sparganosis, etc. In: Fiennes RNT (ed) Pathology of Simian Primates II., 125-143 Karger, Bale.