Balantidium coli in domestic animals: An emerging protozoan pathogen of zoonotic significance

•B. coli is an emerging protozoan pathogen of zoonotic significance affecting a variety of host species.•The disease is endemic in tropical and sub-tropical countries of the world.•Epidemiological surveys should be conducted to know the actual prevalence of B. coli infection in different domestic and wild animal's species. Balantidium coli (B. coli) is an emerging ciliated protozoan parasite of zoonotic importance which causes a disease balantidiasis in a variety of host species including pigs, camels, ruminants, equines and even human. This disease has a cosmopolitan distribution with high prevalence rates in tropical and sub-tropical areas of the world due to favorable geo-climatic conditions for the development and survival of the parasite in these regions. Main reservoir hosts for this pathogen are pigs and animals; acquire infection mainly by the ingestion of the food or water contaminated with the porcine feces. The infected animal manifests clinical signs of anorexia, dehydration, profuse watery diarrhea and retarded growth. Wet mount slide prepared from intestinal scrapings and fecal material is used for the identification of trophozoites and cysts stages of this parasite. PCR can also be used to confirm the parasite. Secnidazole, oxytetracycline and metronidazole have varying efficacy against B. coli infection in various domestic animal species. There is no comprehensive literature available on the occurrence and distribution of the infection at international level. Therefore, the published data between 1989 and 2019 regarding this disease is critically analyzed to provide a detailed overview on this pathogen with special emphasis on geographical distribution of B. coli in domestic animals and different therapeutic agents used to treat this infection. This review will pinpoint the endemic regions which may be a source of potential disease outbreaks and will also help in application of more effectual control strategies against balantidiasis.