626 Vet Pathol 37:626–636 (2000) Mouse Model of Sublethal and Lethal Intraperitoneal Glanders (Burkholderia mallei) D. L. FRITZ,P.VOGEL, D. R. BROWN, 2 D. DESHAZER, AND D. M. WAAG Pathology (DLF, PV 1 ) and Bacteriology (DRB, 2 DD, DMW) Divisions, U.S. Army Medical Research Institute of Infectious Diseases, Fort Detrick, MD Abstract. Sixty male BALB/c mice were inoculated intraperitoneally with either a sublethal or a lethal dose of Burkholderia mallei China 7 strain, then killed at multiple time points postinoculation. Histopathologic changes were qualitatively similar in both groups and consisted of pyogranulomatous inflammation. In sublethal study mice, changes were first seen at 6 hours in mediastinal lymph nodes, then in spleen, liver, peripheral lymph nodes, and bone marrow at day 3. These changes generally reached maximal incidence and severity by day 4 but decreased by comparison in all tissues except the liver. Changes were first seen in lethal study mice also at 6 hours in mediastinal lymph nodes and in spleens. At day 1, changes were present in liver, peripheral lymph nodes, and bone marrow. The incidence and severity of these changes were maximal at day 2. In contrast to sublethal study mice, the incidence and severity of the changes did not decrease through the remainder of the study. The most significant difference between the two groups was the rapid involvement of the spleen in the lethal study mice. Changes indicative of impaired vascular perfusion were more frequently seen in the sublethal study mice. Our findings indicate that mice are susceptible to B. mallei infection and may serve as an appropriate model for glanders infection in a resistant host such as human beings. Additionally, by immu- noelectron microscopy, we showed the presence of type I O-antigenic polysaccharide (capsular) antigen sur- rounding B. mallei. Key words: Burkholderia mallei; capsular antigen; glanders; immunohistochemistry; intraperitoneal inocu- lation; mice; Mus. Glanders is a zoonotic disease caused by Burkhold- eria (formerly Pseudomonas) mallei, a gram-negative, aerobic, non–spore-forming bacillus. Earlier reports 13 stated that B. mallei lacks a capsule; however, there is now evidence to the contrary. 19 This organism is thought to be an obligate mammalian pathogen 22 with solipeds serving as the reservoir for infection. 1,5 While glanders is still endemic in areas of Asia, the Middle East, Northern Africa, as well as various Mediterra- nean regions, 2,13 the Western Hemisphere is currently free of the disease. 2 Natural glanders infections occur primarily in hors- es, donkeys, and mules, 15 but most mammals have some degree of susceptibility. 11 Natural disease is oc- casionally seen in goats, sheep, dogs, and cats, 5,17 and it has been rarely reported in carnivores that have eaten infected horse meat. 5,17 Cattle, pigs, 5 and birds 11 are very resistant to natural disease. Experimentally, most domesticated animals can be infected, with the excep- tion of cattle, pigs, and rats. 11 Guinea pigs and ham- 1 Present address: CMR 431, Box 2113, APO AE 09175. 2 Present address: U.S. Department of Commerce, Bureau of Export Administration, CBTC, Room 2090, 14th Street and Pennsylvania Avenue, N.W., Washington, DC 20030. sters are the laboratory rodents most susceptible to glanders infection. 11 Miller et al. found that, while there appears to be a variance in susceptibility among individual guinea pigs, hamsters are more uniformly susceptible to infection with B. mallei. 15 Vyshelesskii 24 stated his studies showed that cats were most suscep- tible to the species tested, followed by guinea pigs, rabbits, field mice, and moles. Laboratory mice are only slightly susceptible to infection unless the organ- isms are given in very high doses. 18 Even in times when the worldwide prevalence of glanders in horses was high, the occurrence of this disease in human beings was rare. 17 There have been no documented epidemics of glanders in humans. 10 However, the finding of glanders-associated nodules at autopsy in large numbers of people with equine con- tact suggests that the prevalence of mild subclinical infections may be higher than previously suspected. 21 Although human susceptibility to B. mallei has not been studied in depth, the organism has proven to be highly infectious in laboratory settings. 17,22 It has been stated that there are few organisms as dangerous to work with as the glanders bacillus. 17,21 We previously reported a time-course study of glan- ders pathogenesis in Syrian hamsters inoculated intra-
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