Melioidosis

J J VAN DER LUGT

GENERAL INTRODUCTION: GRAM-NEGATIVE AEROBIC OR CAPNOPHILIC RODS AND COCCI Pseudomonas spp. infections

Introduction

Melioidosis is a glanders-like disease of carnivores, rodents, cattle, sheep, goats, pigs, horses and occasionally humans. It is caused by Burkholderia pseudomallei,¹⁰ and is characterized by suppurating or caseous lesions in the lymph nodes and other organs. In South Africa the disease has been reported in a goat8 while the organism was isolated from a white-eared marmoset monkey kept as a pet.⁹ Henning³ quotes McDouell & Varney as reporting the disease in humans in South Africa in 1947. Melioidosis is of little or no importance to the livestock industry in southern Africa.

Aetiology and epidemiology

Burkholderia pseudomallei (syn. Pseudomonas pseudomallei, Malleomyces pseudomallei and Loefflerella pseudomallei) is a Gram-negative, non-spore-forming rod and stains with the common stains. It can readily be isolated aerobically on ordinary culture media at 37 °C.² The bacillus is nutritionally versatile and can be isolated from the soil and water. Infection may therefore arise from the environment rather than by transmission from animal to animal.⁴

Melioidosis is traditionally considered to be endemic between parallels 20 °N and 20 °S of the equator.⁴ A fatal case of the disease in an ox in south-eastern Queensland in Australia is described,⁵ it being postulated that an unusually wet summer with prolonged flooding had favoured the saprophytic growth of the pathogen. In a survey conducted in northern Queensland, ⁷⁵ strains of B. pseudomallei were isolated from 48 animals including birds, pigs, sheep, goats, horses and a kangaroo.⁷

Clinical signs, pathogenesis and pathology

In domestic animals, the disease is usually chronic and progressive with the clinical signs varying according to the location of the lesions.^{3, 8} Sheep and goats may show lameness and may become paralysed in the hindquarters. Suppuration of the nasal mucous membranes, polyarthritis and meningoencephalitis are often seen. Recumbency followed by death after a week is common. The characteristic lesion of the disease comprises small nodules and abscesses in the internal organs, muscles, bones, subcutis and sometimes the mucous membranes of the respiratory system. The progression and development of the disease are thought to be similar to glanders and follow an initial septicaemia and bacteraemia with localization in various organs.¹

Diagnosis, differential diagnosis and control

The typical nodules, multiple abscessation and debilitated condition of the animal may serve to differentiate melioidosis from caseous lymphadenitis in sheep and goats.^{1, 8} Isolation of the bacterium provides a positive diagnosis and the organism is easily cultured from nasal exudates and from suppurating abscesses. A polymerase chain reaction- based method has been developed to detect B. pseudomallei^.6 In horses the disease must be differentiated from strangles (see Strangles) and glanders (see Glanders). In melioidosis of equids there is no lymph node enlargement or involvement of the skin and nasal mucusa.

Although tetracycline has proved effective, treatment should not be undertaken because of the risk of human exposure. Control is based on the elimination of infected animals and the disinfection of premises. No effective vaccine is available.

References

1. BLOOD, D.C., RADOSTITS, O.M. & HENDERSON, J.A., 1983. Veterinary Medicine. 6th edn. London: Baillière Tindall.
2. BUCHANAN, R.E. & GIBBONS, N.E., 1974. Bergey’s Manual of Determinative Bacteriology. 8th edn. Baltimore: The Williams & Wilkins Co.
3. HENNING, M.W., 1956. Animal Diseases in South Africa. 3rd edn. South Africa: Central News Agency Ltd.
4. HOWE, C., SAMPATH, A. & SPOTNITZ, M., 1971. The pseudomallei group: A review. Journal of Infectious Diseases, 124, 598–606.
5. KETTERER, P.J., DONALD, B. & ROGERS, R.J., 1975. Bovine melioidosis in south-eastern Queensland. Australian Veterinary Journal, 51, 395–398
6. SURA, T., SMITH, M.D., COWAN, G.M., WALSH, A.L., WHITE, N.J. & KRISHNA, S., 1997. Polymerase chain reaction for the detection of Burkholderia pseudomallei, Diagnostic Microbiology of Infectious Diseases, 29, 121–127.
7. THOMAS, A.D., 1981. Prevalence of melioidosis in animals in northern Queensland. Australian Veterinary Journal, 57, 146–148.
8. VAN DER LUGT, J.J. & HENTON, M.M., 1995. Melioidosis in a goat. Journal of the South African Veterinary Association, 66, 71–73.
9. VAN DER LUGT, J.J. & HENTON, M.M., 1996. Onderstepoort Veterinary Institute. Unpublished observations.
10. YABUUCHI, E., KOSAKO, Y., OYAIZU, H., YANO, I., HOTTA, H., HASHIMOTO, Y.M., EZAKI, T. & ARAKAWA, M., 1992. Proposal of Burkholderia gen. nov. and transfer of seven species of the genus Pseudomonas homology group II to the new genus, with the type species Burkholderia cepacia (Palleroni and Holmes 1981) comb. nov. Microbiology and Immunology, 36, 1251–1275.