Serodiagnosis of Dermatophilus congolensis infection by counterimmunoelectrophoresis

Sixty-one sera from animals that had contact with Dermatophilus congolensis were examined by comparing three serological methods; counterimmunoelectrophoresis, passive haemagglutination, and agar gel diffusion, and by using four different antigenic extracts of D congolensis. The counterimmunoelectrophoresis was the most satisfactory of the methods having been found to be specific and sensitive, easy to perform and suitable for screening large numbers of samples. It was also found to have a higher antibody detection rate (82.2 per cent) than the other methods thus making it suitable for seroepidemiological surveys. It was found to be capable of detecting multiple antibodies and also revealed dissimilarities among the different antigenic extracts. The cellular antigens of D congolensis were found to detect antibody in more sera than the extracellular antigen; the cell wall extract proved to be the most satisfactory of all, detecting antibody from the largest number of sera compared to the other extracts in all the three serological tests.     

Use of a monoclonal antibody in the diagnosis of infection by Dermatophilus congolensis

A monoclonal antibody (McAb) to Dermatophilus congolensis was produced from murine hybridoma cultures and purified by affinity chromatography. Species specificity was demonstrated using indirect immunofluorescent staining; the McAb was shown to react with 10 D congolensis isolates but not with 10 Nocardia species isolates, a Rhodococcus and a Streptomyces species isolate. The McAb was used to demonstrate D congolensis in clinical material from confirmed bovine and ovine cases and presumptive equine cases of dermatophilosis by indirect immunofluorescent staining.     

Dual infection of a white-tailed deer by Dermatophilus congolensis and Alternaria alternata.

Infection by both Dermatophilus congolensis and Alternaria alternata was found in a 5 1/2-year-old, female white-tailed deer (Odocoileus virginianus). Encrusted lesions characteristic of dermatophilosis were observed on the hocks, flanks, and back. Giemsa-staining of smears of material from beneath the crusts revealed branching filaments, transversely and longitudinally divided into packets of coccoid cells typical of D congolensis. Hyphae morphologically consistent with those of A alternata were found in methenamine-silver- and hematoxylin-and-eosin-stained sections of tissue from the ears, flanks, and back. Nutrient agar cultures inoculated with tissue from an ear and hindlimb of the deer yielded, respectively, A alternata and D congolensis.     

Strain variation in Dermatophilus congolensis demonstrated by cross-protection studies

Cross-protection studies were conducted with vaccines prepared from two isolates of Dermatophilus congolensis (designated strain 1 and strain 2). The vaccines were prepared as either heat-inactivated, washed, formalized filamentous phase bacterium, mixed with alum as an adjuvant, and inoculated intramuscularly (type A vaccine) or sedimented live filaments inoculated intradermally (type B vaccine). The vaccinated sheep were challenged with D. congolensis zoospores of one or other strain. Challenge sites were observed for the presence and severity of lesions. Serum antibody levels to D. congolensis were monitored after vaccination and challenge. Type A and B vaccines from both strains produced some reduction in the severity of lesions when sheep were challenged with strain 1 but not with strain 2. Unvaccinated control sheep developed more severe and persistent lesions when challenged with strain 2 than controls challenged with strain 1. Serum antibody levels to the type B vaccine prepared from strain 1 were significantly higher (P less than 0.05) than antibody levels to type B vaccine from strain 2. These findings showed there was significant variation in virulence and antigenicity between these two isolates of D. congolensis.     

Dermatophilus congolensis Infection in Goats in Tanzania

When goats in Eastern Tanzania were screened for skin diseases, Dermatophilus congolensis was isolated from the skin lesions in 8 of 484 animals examined. In one severely affected case, the disease was also characterized by histological studies (Gram stain, Giemsa stain and routine HE studies) and electron microscopy. The histological picture was characterized by hyperkeratosis, parakeratosis, acanthosis, folliculitis and an inflammatory cellular reaction involving the epidermis. Gram stain and Giemsa stain revealed longitudinal and transverse branching filaments in the deeper layers of the epidermis. Ultrastructural studies demonstrated D. congolensis in various morphological forms, ranging from filamentous to tuber-shaped structures, mixed with numerous coccoid bodies of variable size. In some instances, the organisms were geometrically arranged in parallel rows of beading and were present in and among the degenerated epithelial cells. Several host cells showed degenerative changes. Ticks present on the goats were Amblyomma variegatum, Rhipicephalus evertsi, Rhipicephalus pravus and Boophilus sp. The clinical signs, pathological lesions, diagnosis, epidemiology and pathogenesis of the disease are discussed.     

An outbreak of contagious pustular dermatitis associated with Dermatophilus congolensis infection

Extract

Professional opinion was sought by a Taupo district farmer when he noticed what he took to be advanced cases of scabby mouth amongst one group of 3- to 4-month-old Romney lambs. These affected animals, and other groups of clinically normal lambs, had a 1 been “inoculated” with scab-by mouth vaccine by the farmer, at docking time 11 weeks previously. Most grazing on the farm was improved and in good condition after a wet and warm spring. Only the affected group of lambs and their ewes had been grazing on an unusually fibrous pasture.     

Hemolytic interactions of Dermatophilus congolensis.

The strains of Dermatophilus congolensis grew on blood agar with washed sheep erythrocytes with marked total hemolysis. In testing for hemolytic interactions they gave a significant synergistic effect of a characteristic shape with Rhodococcus equi and Streptococcus agalactiae, whereas with Staphylococcus aureus producing beta hemolysin and with Staphylococcus aureus producing delta hemolysin a simultaneous synergistic as well as antagonistic effect were observed. First of all a conspicuous inhibition of in the beta hemolysin zone began and then the hemolytic effect of D. congolensis was enhanced. A similar double reaction was also observed with Listeria ivanovii. With delta hemolysin there was an inhibition of the hemolytic effect of D. congolensis and at the same time a synergistic effect could be observed. Also D. congolensis gave a weak synergistic effect with Micrococcus lylae and Listeria monocytogenes, and a further weak antagonistic effect with alpha hemolysin of Staphylococcus aureus, Staphylococcus hyicus, Staphylococcus chromogenes and Micrococcus luteus. No interaction of D. congolensis was established with Corynebacterium pseudotuberculosis.     

Isolation of Dermatophilus congolensis from a cat

Dermatophilus congolensis was isolated from a cat with dermatitis. The isolate was sensitive to oxytetracyclin, streptomycin and penicillin but resistant to ampicillin, amoxicillin, gentamycin and cefoperazone.     

Cellular immune responses of the rat to experimental infection with Dermatophilus congolensis

The host cell-mediated immune response was examined following experimentally-induced infection of rats with Dermatophilus congolensis, the causal agent of the skin disease dermatophilosis. Mononuclear cells (MC) isolated from Wistar rats 10 days following the induction of a third infection underwent a strong and specific proliferative response, as assessed by a [3H]thymidine incorporation assay, when cultured with various concentrations of inactivated D. congolensis cocci. Using specific monoclonal antibodies in an indirect fluorescent antibody test, this in vitro response was found to be characterised by a large expansion of the W3/25 (T-helper phenotype) population to form 56% of the total. Finally, the primed and stimulated MC were assessed for their ability to produce factors capable of inhibiting macrophage migration. The culture supernatants of D. congolensis-stimulated MC from infected rats caused significant migration inhibition of normal rat peritoneal exudate cells, whilst the supernatants of similarly-stimulated MC from naive rats failed to cause significant inhibition. The results show that a MC subpopulation becomes primed following experimentally-induced infection with D. congolensis and becomes activated after subsequent, in vitro, exposure.     

Preliminary characterisation of extracellular serine proteases of Dermatophilus congolensis isolates from cattle,sheep and horses

Dermatophilus congolensis is a filamentous branching actinomycete that causes dermatophilosis, an exudative dermatitis in ruminants. The pathogenesis of this disease is poorly understood and virulence factors of D. congolensis have not been characterised. Culture filtrate (CF) of 14 D. congolensis isolates from cattle, 15 from sheep and four from horses were examined for proteolytic activity using azocasein as a non-specific substrate. The isolates were from a variety of geographical locations. All the isolates examined produced extracellular proteolytic activity. CF from 24 and 48 h cultures and from first and third passages contained proteases. Proteolytic activity was greatest in neutral to alkaline pH (pH 7–10). CF of bovine isolates contained more proteolytic activity than that of ovine isolates. Furthermore, in substrate SDS-PAGE gels containing azocasein the number of proteolytic bands and their molecular weights in CF of bovine, ovine and equine isolates were different, giving distinctive band patterns for isolates from each host species. Three out of four bovine isolates from Antigua gave a fourth band pattern. Bands of equivalent molecular weights to the proteases could not be identified in silver stained SDS-PAGE gels of CF. Serine protease inhibitors had a concentration-dependent inhibitory effect on proteolytic activity in CF and inhibited activity of all proteolytic bands in substrate gels. With the exception of EDTA which had a variable-enhancing effect on activity, inhibitors of other classes of protease had no effect on activity. We conclude that D. congolensis produces a number of extracellular alkaline serine proteases, our results suggest the presence of host-specific variation between isolates and to a lesser extent between isolates from the same host species.