Zoonotic Diseases and Phytochemical Medicines for Microbial Infections in Veterinary Science: Current State and Future Perspective

Shin, Bora; Park, Woojun

Although considerable research is being conducted on zoonotic bacteria, there is still a lack of scientific knowledge about the distribution and infection cycles of Chlamydia spp. compared with other zoonotic bacteria. The respiratory illness psittacosis caused by Chlamydia sp. in humans and animals was first reported approximately 100 years ago (33) ; however, only 218 reports on illness were found when searched using "Chlamydial, Zoonoses" in the NCBI database. With the recent occurrences of severe acute respiratory syndrome and avian influenza, studies on Chlamydia infections and zoonoses have increased rapidly, and 53 related papers have been published since 2015. Transmission of C. psittaci infection primarily occurs through inhalation of contaminated aerosols from infected birds (34) . C. trachomatis infection causes reproductive complications, and C. pneumoniae causes respiratory infections and atypical pneumonia in both humans and animals. C. suis infection is associated with diarrhea and failure to gain weight in domestic swine (33, 34) . In general, most people infected with Chlamydia do not show any symptoms (34) . However, in female animals with weak immune systems, pathogens can be transferred to the womb, causing pelvic inflammatory disease, a major cause of ectopic pregnancy and female infertility (33, 34) . Chlamydia infections is most commonly treated by antibiotics, such as azithromycin and doxycycline (33) . However, with antibiotic resistance of pathogenic bacteria becoming a major problem worldwide, there is a need to develop safe drugs with few side effects to treat infection in both humans and animals. In addition, the overuse and misuse of antibiotics are associated with both human and animal immune systems. The collapse of gut microbial ecosystems due to antibiotics could cause undesired negative effects, such as altered physiology of the body or susceptibility to infectious diseases (35, 36) .