Francisella tularensis: a zoonotic pathogen among wild rodents and arthropods - a possible threat in future

Abstract

Francisella tularensis is a Gram-negative coccobacillus and an aerobic bacterium. It causes a zoonotic disease called tularemia in humans. Four subspecies have been found in F. tularensis as F. tularensis subsp. Tularensis (Type A strains), F. tularensis subsp. Holarctica (Type B strains), F. tularensis subsp. mediasiatica, and F. tularensis subsp. Novicida. Rearing rabbits and different kinds of rodents as pets are becoming popular in Sri Lanka, veterinarians need to be knowledgeable on emerging pathogens such as F. tularensis, to diagnose the disease within a short time. Therefore, the objective of this paper is to update veterinarians on possible emerging infections to improve the health of pets and to minimize possible zoonotic infections. The clinical outcome caused by Francisella is a debilitating febrile disease in humans. Francisella has been isolated from hundreds of animal species in the world. Being a diverse host range, associated ecological factors relating transmission of Francisella in the environment is largely unknown. F. tularensis type A was reported to be common in North America while occasionally found in Europe. Type B was found commonly in the Northern hemisphere and in Australia. Tularemia is a sporadic disease, and a small infectious dose is required for an infection in humans. The clinical signs and symptoms of tularaemia depend on the route of infection. Six types of clinical forms were identified as ulceroglandular, glandular, oropharyngeal, oculoglandular, pneumonic and typhoidal in humans. Diagnosis of tularemia in humans is based on epidemiology, clinical findings and laboratory confirmation. Microagglutination test, indirect immunofluorescence assay (IFA) and Enzymelinked immunosorbent assay ELISA are widely used as diagnostic tests. Several conventional and qPCR have been optimized to detect the organism in clinical samples. Antimicrobials such as aminoglycosides, tetracycline, quinolones, and chloramphenicol were used to minimize clinical complications. Utilization of treated water, usage of gloves on handling wild rabbits and rodents, thorough cooking of bush meat, usage of insect repellents, protection of stored food from rodents, wearing masks, ticks-free clothes, keeping away from weeds, cleaning pets from external parasites have been identified as the main preventive strategies against tularaemia in human. No commercial vaccine is found in the market yet against F. tularensis. This can be an emerging and threatening disease in the future with ongoing changes in arthropod parasites in the ecosystem followed by climatic changes in the world.