Histopathological, immunohistochemical, and parasitological studies on pathogenesis of Coenurus cerebralis in sheep

Coenurosis is a major zoonotic parasitic infection, which is caused by Coenurus cerebralis, the larval stage of the tapeworm Taenia multiceps, and is generally observed in small ruminants (17, 18, 24,25,26). The larvae invade the central nervous system of the intermediate hosts, which include sheep, goats, cattle, buffaloes, yaks, pigs, deer, horses, camels, and humans (10, 17, 20, 21, 25, 26). The intermediate hosts become infected by ingesting feed or food contaminated with Taenia multiceps eggs (21). Coenurus cerebralis inhabits the small intestine of the definitive hosts, which include carnivores such as dogs, coyotes, and foxes (17). Coenurosis is observed in either acute or chronic form. The acute form generally occurs in 6- to 8-week-old lambs. Four to five days after the onset of clinical signs, including fever, fatigue, head pressing, and convulsions, death occurs. The chronic form is most common in animals aged 6–18 months. The migration of the parasite to the central nervous system and the development of the parasitic lesions take several months (19). The larvae, which invade the central nervous system and primarily the cerebrum in the intermediate host, develop into transparent cysts, which range between 0.3 and 9.5 cm in diameter and contain a translucent fluid and hundreds of scolices invaginating from the inner wall of the cysts (8). The symptoms associated with coenurosis vary with the location and size of the cysts as well as with the pressure the cysts exert on the cerebrum (12, 20). Coenurus cerebralis firstly causes purulent meningoencephalitis, and once the cyst matures, it leads to central nervous system degeneration which may result in death (7). The most characteristic clinical signs of the disease are observed within the first 2–8 months after the ingestion of the parasite eggs (20) and involve locomotor symptoms (2). As a result of the pressure exerted by the Coenurus cerebralis cysts on the cerebrum but depending on the location of the cysts in the central nervous system, the animal hangs its head to the side where the cyst is located, walks in circles, and knocks against surrounding objects as it is unable to hold its head upright. Furthermore, various other clinical symptoms, including ataxia, incoordination, paresis, torticollis, teeth grinding, blindness, coma, cerebral atrophy, and deformation and thinning of the cranial bones may also be observed (3, 11, 14). Clinical symptoms may be suggestive of the disease, yet definitive diagnosis is made on the basis of the detection of parasite cysts in the cerebrum (20). While 80%–90% of the cysts are localised in the cerebral hemispheres, 5%–10% are located in the cerebellum (19). This study was aimed at demonstrating the morphology and histopathology of coenurosis and characterising the inflammatory response of the host to the parasite.

The cerebral and cerebellar tissues of 15 sheep and lambs of different breeds and ages were submitted to the Pathology Department of Harran University, Faculty of Veterinary Medicine for necropsy. These tissues, necropsied between 2012 and 2016 in the Sanliurfa region of Turkey, constituted the material of the study.

Coenurosis, which is generally observed in small ruminants, remains a major and common parasitic infection (19). Coenurosis is a zoonotic parasitic disease of sheep and goats, which is caused by Coenurus cerebralis, the larval stage of Taenia multiceps. Coenurus cerebralis, which can be fatal for sheep and goats, inhabits the small intestine of its definitive hosts, which include carnivores such as dogs, coyotes, and foxes (17).

Some researchers have reported that the parasite cysts are mostly localised to the parieto-occipital region (10). The present study demonstrated that the cysts were located in the frontal and parietal lobes of the cerebral tissue. This finding suggests that the parasite cysts may develop in any region of the central nervous system. The size of Coenurus cerebralis cysts has been reported to range between 0.5 and 4.2 cm by Biyikoğlu (5), 1.7–6.3 cm by Akkaya et al. (3), and 0.8–6.5 cm by Achenef et al. (1). In the present study, while the largest cyst measured 6 × 5 cm, the smallest cyst was 2 × 2 cm in size. In previous research, the prevalence of Coenurus cerebralis was reported as 36.8% in sheep in Turkey (23), 15.5% in the Kars region of Turkey (9), 45.6% (sheep) and 43.3% (goats) in Tanzania (13), 18.65% in Iran (22), and 14.8% in Mozambique (4). In the present study, the highest and lowest numbers of scolices detected in the cysts were 55 and 21, and the number of rostellar hooks in the scolices ranged between 22 and 30. RT-PCR and PCR results confirmed that the parasite was the larval stage of Taenia multiceps, and the parasitological results obtained were found to be in agreement with those reported in former research (1).

Several literature reports are available on the histopathological investigation of parasite cysts localised to the cerebral and cerebellar tissues and the inflammatory lesions in the periphery of these cysts. In agreement with previous research (11, 14, 23), in the present study histopathological examination demonstrated a marked hyperaemia around the cyst, foreign body giant cells, moderate mononuclear cell infiltration, and in some sections calcification in the periphery of the cysts, as well as perivascular cuffing, mild microgliosis and astrocytosis in the white matter near the cysts, and also demyelination, degeneration of a few neurons, necrosis, non-purulent meningitis, and hyperaemia of the meningeal blood vessels.

To the authors’ knowledge, there is no previous microscopic study on the inflammatory cells surrounding coenurosis lesions in the central nervous system. In order to reach the goal of demonstrating the distribution of inflammatory cells in the parasitic granulomatous inflammation due to Coenurus cerebralis, immunohistochemistry was employed on CD3 for T cells, CD79 for B cells, CD163 for macrophage cells, and GFAP for neurodegenerative cells. This study was designed to provide information on this particular topic, on the CD3-, CD79α-, and CD163-positive cells found in the periphery of the lesions and in the tissue parenchyma, and on the presence of the more proliferatively expressed GFAP as demonstrated with immunohistochemical staining methods (15). Granulomatous inflammation is best defined as a special variety of chronic inflammation in which cells of the mononuclear phagocyte system are predominant and take the form of macrophages, epithelioid cells, and multinucleated giant cells. In addition there is usually an admixture of other cells, especially lymphocytes, plasma cells, and fibroblasts (27). In this study, immunohistochemical examination revealed that macrophages (CD163+) were the dominating cell population in the inflammatory reaction observed in the lesions. Furthermore, it was determined that the expression of GFAP had increased, which is produced by astrocytes that are activated in the event of neurodegenerative disorders. The difference observed between the immunohistochemically stained cells was found to be statistically significant (P < 0.001), confirming these results. In particular, the quantitative differences determined between the staining intensity of the cells involved in the cellular immune response, such as macrophages (CD163), T lymphocytes (CD3), and B lymphocytes (CD79α) suggest that in parasitic infections like coenurosis which cause chronic granulomatous lesions the predominating cell type is the macrophage.

It is hoped that the results of the present study will light the way for future pathological and parasitological research to be conducted on this subject.