Francisella Tularensis, A Zoonotic Risk from Wild Rodents and Arthropods, Possible Threat in Future with Continuing Climatic Changes
Francisella tularensis is a Gram-negative coccobacillus and an aerobic bacterium. It causes a zoonotic disease called tularemia in human. Four subspecies have been found in Francisella tularensis as Francisella tularensis subsp. Tularensis (Type A strains), Francisella tularensis subsp. Holarctica (Type B strains), Francisella tularensis subsp. mediasiatica, and Francisella tularensis subsp. Novicida. The disease is called as tularemia which is a debilitating febrile disease in human. Francisella has been isolated from hundreds of animal species in the world. As a results of diverse host range observed, ecological factors relating transmission of Francisella in the environment is largely unclear. Francisella tularensis type A has been reported common in North America while occasionally found in some countries of Europe. Type B has been found common in Northern hemisphere and found in Australia as well. Type A has been reported severe clinical diseases than type B in human.
Tularemia is a sporadic disease with small infectious dose required. The symptom of tularaemia depends on route of infection, altogether six main clinical forms were identified as ulceroglandular, glandular, oropharyngeal, oculoglandular, pneumonic and typhoidal form in human. Diagnosis of tularemia in human is based on clinical finding, epidemiology, and serological testing. Micro agglutination test, Indirect Immunofluorescence Assay (IFA), and ELISA is used widely used as diagnostic test on tularemia. Several conventional, multiplex PCR assays and qPCR has been optimized to diagnose the organism in clinical submission. Antimicrobials are used widely to minimize the complication of the infection and aminoglycosides, tetracyclines, quinolones, and chloramphenicol with high relapse rates of 10-21 days.
Utilization of treated water for daily activities, usage of gloves when handling wild rabbits and rodents, thoroughly cooking of bush meat, using of repellent on insect specially traveling outside, protection of food at storage from rodents, wearing mask, checking the cloths for ticks, avoid touching of weed when traveling in natural trails, cleaned pets without ticks and other external parasites, vaccination of veterinarian and other staff who contacts animals and livestock are alternative preventing strategies against tularaemia in human. Vaccination of live attenuated, killed or subunit vaccines are an alternative method to control the infection in endemic regions with variable success. No commercial vaccine is found in the market. Francisella tularensis can be emerging and threatening disease in future with ongoing changes in arthropod parasites in the ecosystem followed by climatic changes in the world.