Francisella Tularensis

Francisella Tularensis


Nature of the Menace and Global Incidence

New, re-emerging and microbiologic infections threaten the health of peoples, including those in the industrialized world, according to world health entities (Cutler et al., 2010). The World Health Organization, the Food and Agriculture Organization and the World Organization for Animal Health in 2004 recognized these threats as 60% zoonotic, or coming from animals. The entities described the cause, zoonosis, as a newly recognized or newly evolved or re-emerging pathogen with increased incidence or expansion in terms of geography, host or vector. They also estimated that 71% of these are wildlife animals, which can switch hosts by changing genetic combinations or adapting behavior or socio-economic, environmental or ecologic characteristics of new hosts. By continuous alterations and adaptations with human and animal hosts and modes, new and recurring diseases may develop (Cutler et al.).

Many of these are opportunistic and spread with increasing demands for protein foods through increased farming (Cutler et al., 2010). The infections are transmitted by the animals during farming, hunting or bites. Arthropod vectors have been observed to transmit these infections large-scale, as in the cases of West Nile fever and plague. Changes in farming, lifestyle and transportation also enhance the environment of these infections. They are able to mutate, recombine, select and develop new traits by deliberate manipulation. These can result in epidemics. Global health authorities see the re-emergence of these opportunistic infections through host switching as a major source of human infectious disease. The measures contemplated are strategies to improve public health through improved surveillance in areas with the highest incidence or likelihood of re-emergence. The measures include better detection in reservoirs, early detection of outbreak, identification of factors of re-emergence, and effective control (Cutler et al.).

Method of Detection

Tularemia is a zoonosis and the infecting agent is Francisella Tularensis (Carvallo et

Al, 2007). Francisella tularensis or FT is also a potential agent of bioterrorism (Seibold et al., 2010). The MALDI-TOF-MS method isolated 5 representative subspecies of FT, such as Francisella philomiragia, tularensis, holarctica, ediasiatica, and novicida from 45 blind-coded Francisella strains from a database of 3, 287 spectra of microorganisms (Seibold et al.). FT is considered a formidable biologic agent in that it occurs naturally throughout North America (Farlow et al., 2005). An investigation of 161 tularensis isolates revealed 126 unique genotypes. The results were similar to those reported globally. Two distinct sub-populations occur primarily in the central United States and in the western United States, respectively. In the first half of the 20th century, hundreds of thousands of rabbits and hares were moved from central to the eastern States, including carcasses infected with FT. There were no reported cases in Massachusetts before 1937. This suggests that the transport of cottontail rabbits for sports may have spread the FT pathogen in the United States (Farlow, et al.).

Incidence in the United States

The overall incidence of the FT subspecies tularensis among humans in the United States appeared to be prevalent among the central sub-populations (Farlow et al., 2005). The areas considered hot spots for the infection were Arkansas, Kansas, Massachusetts, Missouri, Oklahoma and South Dakota. The spread was the likely result of the successful grouping of the subspecies if not favorable environmental conditions to disease maintenance and transmission in the region (Farlow et al.).

Epidemiologic and Molecular Analysis

Comparative clinical trials of human tularemia cases from 1964 to 2004 in 39 States showed that 2 subspecies account for Tularemia in the United States (Staples et al., 2006). These are subspecies a tularensis and subspecies B. holarctica. Subspecies infections differ according to geographical distribution, disease outcomes and spread. The study found that type a in the western regions were less severe than type B and type a infections in the eastern regions. The combined epidemiologic and molecular approach may lead to new findings and insights on the disease (Staples et al.).

The comparative trials revealed that type a infections in the eastern regions are 14% more severe than type B and 0% for type a in the western regions (Staples et al., 2006). Type a-east and type B isolates quite likely drew from patients' lungs or blood, while type a-west, from lymph nodes. Type a-west may be milder than the others because of different virulence factors or infectious does, depending in turn on different modes of transmission. These 3 subspecies seem to favor different ecological conditions. Type B prefers waterways, like the upper Mississippi River, and those with high rainfall, like the Pacific Northwest coastal areas. Type a-west abounds in the arid regions like the Rocky Mountains. And Type a-east tends to occur in the central southern States and the Atlantic Coast. But 50% of all reported cases of human tularemia nationwide were in the central southeast region, making the region a major focus. Type a-east cases may be associated with the importation of rabbits from Arkansas, Oklahoma, Missouri, and Kansas or with hunting clubs in Massachusetts, Pennsylvania, New Jersey, and Maryland in the 1920s and 1930s (Staples et al.).

Type a isolates are often linked with rabbits and hares and type B with rodents (Staples et al., 2006). Human Type a-east and type a-west infections were attributed to exposures to rabbits and hares and human type B, to rodents. But both infections may be due to exposure to cats. Ticks were also found to be capable of transmitting either type to human beings. Type a-west infections may also be transmitted by biting flies (Staples et al.).

Upon exposure to aerosolized F. tularensis, the person develops a fever with or without respiratory symptoms in 3 to 5 days (Buehler et al., 2003). This is followed quite fast by life-threatening pneumonitis and an equally fast increase in the number of cases exposed. This triggers syndromic surveillance alarms, which will invite suspicion. FT is slow-growing and takes up to 5 days before detection. It is detectable only after inoculation in a routinely processed blood culture. Special lab techniques are necessary. Detection is further delayed if there is no clinical suspicion. In case of an epidemic, specific antibiotic treatment should be administered among those with fever (Buehler et al.).

Molecular Detection in Natural Waters

Francisella Tularensis has long been the cause of persistent and endemic disease Tularemia in some parts of Northern Sweden where subspecies holarctica occurs (Broman et al., 2010). PCR screening was conducted for three years on water and sediment samples in two areas in Sweden with the endemic disease revealed the presence of tularensis subspecies holarctica during outbreak and non-outbreak years.

These sequences were detected in water sampled during both outbreaks and non-outbreak years. The findings provided evidence for the persistent occurrence of the subspecies in the natural waters and sediments of the said areas (Broman et al.).

This subspecies is found throughout the Northern Hemisphere and recognized as a potential bioterrorism agent (Broman et al., 2010). It is a complex structure and uses many and potential vectors to spread as a disease agent. Tularemia has been detected among approximately 250 wildlife species of animals. Among these are blood-sucking arthropods like ticks, tabanid flies, midges, mites, fleas, lice and mosquitoes. The holarctica subspecies strain has been endemic in northern Sweden where major transmission vectors are infected mosquitoes belonging to the Aedes cinereus strain. This FT subspecies strain favors water environments, such as streams, ponds, lakes and rivers. The subspecies holarctica thrives in watercourses and in association with protozoa, on which it preys (Broman et al.).

Surveillance System for Bioterrorist Attacks

More and more public health departments are acquiring new surveillance systems to promptly detect the earliest indications of bioterrorism disease (Buehler et al., 2003). It is not known if these systems will work as hoped. The detection of bioterrorism-related epidemic depends on population characteristics, use and availability of health services, the nature of an attack, epidemiology of the disease, surveillance methods and the response capabilities of the health department. While it may be impossible to predict the blending of these factors in an attack, their probable effect on epidemic detection can help. The factors can determine the usefulness of syndromic surveillance and the approaches to increasing doctors' and clinicians' recognition of these towards a reporting of an epidemic (Buehler et al.).

Preparedness for Bioterrorism

A biologic attack against civilian populations is now a recognized real threat and naturally occurring infectious agents and their products are likely implements in the activity (Relman & Olson, 2001). Physicians need to be trained to become familiar with these toxic agents and the diseases they cause. They need to recognize when a deliberate attack is imminent and to manage its consequences. Physicians infrequently discuss biologic warfare of bioterrorism among themselves despite the attention given by the media, politicians and military officials. Most of them have not encountered the deadly use of biologic agents or treat a victim of a biologic attack. As these agents occur only in a fit biological environment, physicians and other clinicians seldom encounter these in disease conditions (Relman & Olson).

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