HISTOPHILUS OVIS INFECTION IN SHEEP IN WESTERN VICTORIA

Abstract

Organisms resembling Histophilus ovis were isolated from sheep in Western Victoria in association with synovitis, septicaemia and/or abscessation in 2 to 8 week old lambs. Histopathological lesions in these lambs were indicative of bacterial embolism with thrombosis. Similar organisms were also isolated from sheep in 2 flocks with a high neonatal mortality rate. These isolations were from vaginal swabs from the ewes, placentas and from one lamb which had meningitis, ependymitis, choroid plexitis, hepatic necrosis and focal myocarditis. The morphology, cultural characteristics and biochemical activity of the organisms are described and it is suggested that the organisms may be better classified in the genus Actinobacillus.

Proposal of Histophilus somni gen. nov., sp. nov. for the three species incertae sedis ‘Haemophilus somnus’, ‘Haemophilus agni’ and ‘Histophilus ovis’

“…Phenotypically similar bacteria had previously been isolated from sheep; for example, an organism named 'Histophilus ovis' had already been isolated (Mitchell, 1925), but this isolate is no longer available. In 1956, 'Histophilus ovis' was isolated from mastitis in sheep (Roberts, 1956) and has since been isolated from ovine septicaemia, synovitis and epididymitis and from ovine vaginas (Rahaley & White, 1977;Rahaley, 1978). In 1958, a bacterium was isolated from lambs with septicaemia in Australia and designated 'Haemophilus agni' (Kennedy et al, 1958).…”

Acquisition of haemoglobin-bound iron by Histophilus somni

“…H. somni is a fastidious and slow-growing organism with low biochemical activity. H. somni is associated with a variety of conditions such as septicaemia, myocarditis, arthritis, pyaemia, mastitis, metritis, abortion, neonatal mortality, decreased fertility in ewes and rams, epididymo-orchitis, pneumo nia and thrombotic meningoencephalitis (Robert, 1956;Rahaley and White, 1977;Rahaley, 1978a;Webb, 1983b;Harris and Janzen, 1989;Philbey et al 1991;Cassidy et al, 1997). H. somni has aIso been iso lated from the vagina and vaginal fluids of c1inicaUy normal ewes (Rahaley, 1978b;Higgins et al, 1981;Harris and Janzen, 1989) and it has been suggested that the genital (Webb, 1983b) and respiratory (Philbey et al, 1991) tracts are the natural habitats of H. somni.…”

Evidence of Host-Specific Subgroups among "Histophilus ovis" Isolates

“…Among the nearly 500 strains which have been characterized by differential tests and reported in the literature (1,4,5,7,10,14,17,18,(21)(22)(23)(24)(25)28), variability has been noted in practically all of the key biochemical and cultural features that have been described. These include oxidase (28) and catalase tests (1, 5 ) , raised carbon dioxide requirement (1,26), hemolytic activity (5,22), indole production (1,5,14,18,20,25), decarboxylase tests (7,21), reduction of nitrate (9, esculin hydrolysis (21,22), and acid production from carbohydrates (24).…”

“…These include oxidase (28) and catalase tests (1, 5 ) , raised carbon dioxide requirement (1,26), hemolytic activity (5,22), indole production (1,5,14,18,20,25), decarboxylase tests (7,21), reduction of nitrate (9, esculin hydrolysis (21,22), and acid production from carbohydrates (24). These variations often appear to be related to strain origin by host species.…”