Histological comparison of malignant epithelioid mesothelioma in young and adult cattle.

The histology and immunohistochemistry of pleomorphic and conventional epithelioid mesotheliomas were examined. The former was detected in two young calves aged 2 and 4 months and was characterized by pleomorphic and atypical cells with decreased expression of cytokeratin 7 (CK7). In contrast, the latter was found in a 31-month-old heifer, consisting of tumor cells uniform in size and shape with CK7 expression in nearly all cells. Production of collagen by tumor cells was demonstrated in both histological types, and was considered to be characteristic of bovine epithelioid mesothelioma. Pleomorphic mesothelioma is far more pleomorphic and mitotically active than conventional mesothelioma, and its normal counterpart may be immature mesothelial cells with high proliferation potential, which exist in fetal life and early calfhood.

Characterization of Sarcocystis fayeri's actin-depolymerizing factor as a toxin that causes diarrhea.

Raw horsemeat has the potential to induce food poisoning which often presents with diarrheal symptoms. A sample of horsemeat was found to be infected with Sarcocystis fayeri, and a 15-kDa protein isolated from the cysts of S. fayeri was found to clearly show its diarrhea-inducing activity. A nested polymerase chain reaction was used to clone the cDNA of the 15-kDa protein. The deduced amino acid sequence showed homology to actin-depolymerizing factor (ADF). A recombinant 15-kDa protein depolymerized prepolymerized actins in a test tube. The 15-kDa protein possessed conserved amino acid sequences of ADF of Toxoplasma gondii and Eimeria tenella. These characteristics indicate that the 15-kDa protein of S. fayeri belongs to the ADF/cofilin protein family. The recombinant 15-kDa protein evoked fluid accumulation in the looped ileum, resulting in diarrhea, but it did not kill the cultured fibroblast cells, macrophages or intestinal mucosal cells. In addition, the culture supernatant of the macrophages treated with the recombinant 15-kDa protein killed the fibroblast L929 cells. This fact indicates that ADF of S. fayeri induced cytotoxic substances, such as tumor necrosis factor-α, according to the published reports. Although further experiments are needed now to elucidate the enterotoxic mechanism of S. fayeri's ADF, our findings may offer new insight into research on parasites and parasite-instigated food poisoning.

A toxin isolated from Sarcocystis fayeri in raw horsemeat may be responsible for food poisoning.

Food poisoning has been reported after the consumption of raw horsemeat in Japan. Diarrhea with a short incubation period is a common symptom in such cases of food poisoning. Cysts found in horsemeat ingested by patients have been identified as Sarcocystis fayeri based on morphological and genetic evaluation and findings from experimental feeding of cysts to dogs, which resulted in the excretion of sporocysts. The extracts of the horsemeat containing the cysts produced a positive enterotoxic response in the rabbit ileal loop test. Intravenous injection of a 15-kDa protein isolated from the cysts induced diarrhea and lethal toxicity in rabbits, and the protein produced enterotoxicity in the ileal loop test as did the extracts of the horsemeat containing the cysts. The partial amino acid sequence of the 15-kDa protein was homologous to the actin-depolymerizing factor of Toxoplasma gondii and Eimeria tenella. These findings indicate that the 15-kDa protein of S. fayeri is a toxin that causes food poisoning after consumption of parasitized horsemeat.

[Control of toxicity of Sarcocystis fayeri in horsemeat by freezing treatment and prevention of food poisoning caused by raw consumption of horsemeat].

More than 27 outbreaks per year of food poisoning caused by consuming horse meat were reported in Kumamoto Prefecture (including Kumamoto City) from January 2009 to September 2011. It was found that the causative agent of the outbreaks was a protein with a molecular weight of 15 kDa that had originated from bradyzoites of Sarcocystis fayeri parasitizing the horse meat. Rabit ileal loop tests showed that pepsin treatment of homogenates of frozen horse meat containing the cysts of S. fayeri induced loss of toxicity, presumably by digestion of the proteinous causative agent(s). Slices of horse meat containing the cysts were frozen at below -20°C for various periods. The cysts were collected after thawing the slices, then treated in an artificial stomach juice containing pepsin. The bradyzoites of the cysts kept at -20°C for 48 hr or more completely disappeared. Simultaneously, the 15 kDa protein also disappeared in the frozen cysts. After notifying the public and recommending freezing treatment of horse meat, no subsequent cases of food poisoning were reported. This indicates that freezing of horse meat is effective to prevent the occurrence of food poisoning caused by consuming raw horse meat containing S. fayeri.