zoonoses and communicable diseases common to ... - PAHO/WHO

TULAREMIA 275TULAREMIAICD-10 A21.0 ulceroglandular tularaemia; A21.1 oculoglandular tularaemia;A21.2 pulmonary tularaemia; A21.7 generalized tularaemia;A21.8 other forms of tularaemiaSynonyms: Francis’ disease, deer-fly fever, rabbit fever, Ohara’s disease.Etiology: Francisella tularensis, a highly pleomorphic, gram-positive, nonmotilebacillus; it has a fine capsule and can survive for several months in water, mud, anddecomposing cadavers.Two biovars are recognized: F. tularensis biovar tularensis (Jellison type A) and F.tularensis biovar palaearctica (Jellison type B). Names have also been suggested forsome local biovars, such as mediaasiatica (Olsufjev and Meshcheryakova, 1982) andjaponica. Classification into biovars is not based on antigenic differences, but on theagent’s biochemical, virulence, and ecologic characteristics, and its nosography.Geographic Distribution: Natural foci of infection are found in the NorthernHemisphere. In the Americas, the disease has been confirmed in Canada, the US, andMexico. It is found in most European countries, Tunisia, Turkey, Israel, Iran, China,and Japan. In the former Soviet Union, there are extensive areas with natural foci.F. tularensis biovar tularensis predominates in North America and causes 70% to90% of human cases in that part of the world. The principal sources of infection bythis biovar are lagomorphs (mainly those of the genus Sylvilagus) and ticks. Biovarpalaearctica (syn. holarctica) causes 10% to 30% of human cases; its principalhosts are rodents. Biovar tularensis is more virulent than biovar palaearctica (Belland Reilly, 1981).Biovar palaearctica is found in western and northern Europe, Siberia, theFar East, in some parts of central Europe, and less frequently, in North America.Biovar palaearctica is distributed in natural foci among Rodentia spp. andLagomorpha spp. In the Asian part of the former Soviet Union, where there are naturalfoci among Lepus and Gerbilinae, the name F. tularensis var. mediaasiaticahas been suggested for the etiologic agent. This biovar, like palaearctica, is moderatelyvirulent. Genetic studies have shown that the mediaasiatica and japonicavarieties hybridize with F. tularensis var. tularensis, indicating the possibility ofgenetically related strains outside of North America. The strains of Central Asiadiffer from the two main biovars in their glucose fermentation properties(Sandström et al., 1992).Occurrence in Man: It is not an internationally reportable disease and its globalincidence is hard to establish. The countries with the best data are the US and theformer Soviet Union. In both, the number of human cases has apparently declinedsharply. In the former Soviet Union, where in the 1940s some 100,000 cases werereported annually, the incidence has diminished to a few hundred cases per year. Inthe US, the average number of annual cases fell from 1,184 in the 1940s to some274 cases between 1960 and 1969 and has continued to fall.In the period 1977–1986, the average number of cases per year was 225. Manymild cases are not reported (Rohrbach, 1988). Current incidence is approximately