Dermatophilus Congolensis Research Articles

A micro-challenge technique for the study of resistance to Dermatophilus congolensis in Merino sheep

The clinical response (erythema, oedema, scab formation) of sheep to a micro-challenge with zoospores of Dermatophilus congolenis is described. The effect of site preparation (wax removal), dose of zoospores applied (0, 1 x 106, 1 x 107, 1 x 109, 1 x 1010. zoospores/mL), and day of inspection after challenge (0, 2, 4, 7, 9, 13, 17, 20, 23 days) were the major factors accounting for differences in responses to challenge. At all doses, large differences were observed between sheep in the prevalence, severity, and persistence of infection. These differences were not due to the effects of flock, or to footrot resistant and susceptible phenotypes. Based on results from this work, modifications were proposed to allow large numbers of sheep to be tested to estimate genetic differences between sheep in their resistance to challenge with zoospores from D. congolensis.

Réponses cellulaires dans la, dermatophilose expérimentale chronique et aiguë de moutons

The cellular infiltrate into the dermis in dermatophilosis lesions is composed of a range of cell types. The aim of this study was to establish if the composition of the cellular infiltrate in chronic lesions was different from that in healing lesions. Experimental Dermatophilus congolensis infections of sheep were used to study the sequential changes in cell types during the course of chronic and acute infections. Infestations of adult Amblyomma variegatum ticks were used to produce chronic lesions on infected sheep, infections of tick-free sheep provided acute lesions. Histopathology and immunohistochemistry were used to stain and label cell types in the dermis of infection sites. Neutrophils dominated the early response and were present in larger numbers in chronic lesions. Plasma cells were present in both types of lesion, however they persisted in chronic lesions but disappeared from the skin at acute lesion sites after the lesions had resolved. There were 2-3 times as many mononuclear cells in chronic than acute lesions from as early as 4 days post infection and these cells persisted in the chronic lesions. In the chronic lesions the mononuclear cell population was composed of T-helper and T-cytotoxic/suppressor lymphocytes in equal proportions whereas in acute lesions at 14 days post infection, when lesion resolution is underway, there were greater numbers of T-helper cells than T-cytotoxic/suppressor cells.

Utilisation de modèles souris pour la dermatophilose expérimentale

Gnotobiotic mice with congenital immune deficiencies were infected with the skin pathogen Dermatophilus congolensis. Athymic (nude) mice with T cell deficiency were less susceptible than nude mice which also carried the beige mutation (beige-nude) with NK cell and granulocyte defects, as part of the murine equivalent of Chediak-Higashi syndrome. The additional presence of the x-linked immunodeficiency gene in other beige mutant mice, giving reduced B cell responsiveness, did not increase their susceptibility. BALB/c mice with the nude mutation and evidence of macrophage insufficiency, had a moderate level of susceptibility, greater than that of outbred nude mice but less than that of beige, nude mice. The appearance of the lesions on the haired mice was different from that on those with hairless skin (nude and beige-nude). On the haired mice thin crusts developed and healed rapidly, while on the hairless mice the lesions started as nodules and later progressed to crusts. The nude BALB/c mice developed atypical lesions, which resembled ulcers. Germ-free nude and beige-nude mice showed the same types and time course of infection as the gnotobiotic animals, suggesting that bacterial interference, by a limited skin flora, did not play a major role in defence against D. congolensis. However, bacteriological analysis indicated that D. congolensis could survive in the gut of germ-free mice. This work emphasizes the importance of non-specific immune mechanisms, such as epidermal hyperproliferation and the neutrophil, in resistance to D. congolensis.

L’effet systémique des adultes et des nymphes d’<em>Amblyomma variegatum</em> sur la pathogénie de la dermatophilose

The systemic effect of adult and nymphal Amblyomma variegatum on the pathogenesis of experimental infections of Dermatophilus congolensis was investigated. Three groups of four sheep were used with all 12 sheep being infected with identical titrated doses of D. congolensis One group of sheep was simultaneously infested with adult A. variegatum the second with nymphal A. variegatum and the third group were the controls, with no exposure to ticks. Assessment of the resulting infections indicate that the systemic effect of this tick is confined to the adults. Skin and serological tests using foreign antigens showed significantly reduced cell mediated and humoral immune response only in the sheep infested with adult A. variegatum.

Dermatophilosis in camels (Camelus dromedarius Linnaeus, 1758) in Kenya.

Natural dermatophilosis (caused by Dermatophilus congolensis Van Saceghem, 1915) has only recently been described in camels (Camelus dromedarius). Further work has shown that the disease is actually widespread. At the Ol Maisor farm where it was first diagnosed (in the Laikipia district of northern Kenya), detailed investigations have revealed that thirty camels (ten calves and twenty adult animals) were infected. The signs varied from mild to more than 50% skin involvement. Patches of wool on the rump were easily detachable with many hard, white crusts. Similarly, another twenty camels from a totally different area of northern Kenya (Samburu district) were found to be infected with D. congolensis. Bacterial isolation was used to confirm the diagnosis. At Ol Maisor farm, twenty sheep were also found to have severe dermatophilosis. There were scabs and many areas of wool shedding. The shed wool had crusts similar to those observed on camels. Experimental infection with D. congolensis isolated from camels was conducted, by means of scarification, on the skin of two goats. The same experimental infection was possible in two calves, taking two weeks to become established. After thirty days there were disseminated foci of infection on the heads of the calves, especially around the eyes. Although these findings cannot show the actual source of D. congolensis, it is possible that the same organism causes dermatophilosis in the different animals.

Immunodominant antigens of zoospores from ovine isolates of Dermatophilus congolensis

Zoospores of Dermatophilus congolensis were analysed by SDS-PAGE and western blotting. The electrophoretic profiles of zoospores from 13 isolates of D. congolensis were similar but not identical when stained with Coomassie blue or silver. Immunodominant polypeptides with apparent molecular masses of 76 and 31 kDa were identified in western blots of 13 of 13 and 12 of 13 isolates respectively of D. congolensis reacted with hyperimmune, ovine, antizoospore sera. Identical immunodominant polypeptides were observed in western blots reacted with sera obtained from naturally infected sheep. Initial characterisation of the 76 and 13 kDa polypeptides indicated that they were probably surface exposed because (i) antibodies eluted from the surface of live zoospores after adsorption of hyperimmune antizoospore serum, reacted principally against the 76 and 31 kDa subunit polypeptides in western blots, (ii) adsorption of hyperimmune antizoospore serum with live zoospores resulted in significant diminution of reactivity against both the 76 and 13 kDa polypeptides in western blots, (iii) indirect fluorescent immunostaining of zoospores with antiserum prepared against gel-purified 76 kDa polypeptide, resulted in intense staining of the zoospore outer coat. Immuno-gold electron microscopy of negatively stained zoospores with antiserum prepared against gel-purified 31 kDa polypeptide identified this antigen as a flagella subunit.

Relationship between chronic ovine dermatophilosis and levels of T6 lymphocyte antigen staining in peripheral blood mononuclear cells

Quantification of a T6-lymphocyte antigen in peripheral blood mononuclear cells of sheep was used to select 15 from 48 one year old Merino ewes not previously exposed to Dermatophilus congolensis infection. These sheep were compared in response to challenge with D. congolensis zoospores and levels of T-6 lymphocyte antigen in peripheral blood mononuclear cells with 15 Merino ewes of similar age and strain from a different site that had been treated and recovered from chronic dermatophilosis. The T-6 lymphocyte antigen level were significantly lower in the chronic dermatophilosis sheep and they developed significantly more severe lesions than the selected, previously unexposed sheep despite the former sheep having high serum antibody levels to D. congolensis. Measurement of the fleece characteristics, wax and suint concentration showed no differences between the groups that might have explained the considerable differences in their susceptibility to dermatophilosis.

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.

Experimental Dermatophilosis

The histopathologic features of an experimental dermatophilosis of rabbit skin were described. The strain of Dermatophilus congolensis used for the experimental infection was obtained from the unique isolation and cultivation of this actinomycete from the ulcerous leg lesion of one male patient. Further strains in experiment came from the collections of type cultures. The experimental infection was characterized as an exudative and crustal dermatitis with acanthosis and subcorneal abscesses. Branching hyphae and clusters of coccoid bodies were found mostly in the parakeratotic layer and infrequently in the abscesses. Both the coccoid bodies and the hyphae were Gram-positive. The hyphae were acid-fast but the coccoid bodies were non-acid-fast. The fine structure of hyphae and coccoid bodies, namely of those with flagella, was also described by means of a transmission and scanning electron microscope.

Survival of Dermatophilus congolensis in tropical clay soils submitted to different water potentials

The survival of a rifampicin-resistant mutant of Dermatophilus congolensis in vertisol and oxisol soils from Guadeloupe and in their constitutive clays was studied using a pneumatic device for controlling water potentials (pF). Experiments were carried out at two pF values simulating the wet season and the dry season. Survival time depended on the type of soil and its water content. Organic matter had a protective effect on the microorganism in oxisol but not in vertisol. The pathogenicity of D. congolensis was preserved in the soils which could therefore act as temporary reservoirs of this pathogen. Long-term survival of this organism in soils mixed with water suggests that ponds and dipping tanks may constitute sources of infection for cattle.

Strain variation in Dermatophilus congolensis demonstrated by cross-protection studies

Cross-protection studies were conducted with vaccines prepared from two isolates 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<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.

The Effect of Malnutrition on Vaccination Against Dermatophilus congolensis Infection in Ruminants

Vaccination against Dermatophilus congolensis was carried out in groups of lambs raised on optimal or energy deficient diets. The groups differed significantly in weight, body condition score and plasma total protein and albumin. All animals were then challenged with D. congolensis in a dose response infection model. The vaccine was effective in the well nourished animals, reducing the number of affected lambs in the vaccinated group and the severity of the lesions and increasing the minimum dose required to cause infection. In contrast, all of the vaccinated energy-deficient lambs developed lesions. There was some evidence of vaccine effect in these animals but this was not as marked as that seen in the well nourished lambs. The malnourished lambs, vaccinated and non-vaccinated, took longer to heal than the well nourished groups. Resistance to challenge was not associated with serum antibodies or skin test reactivity to D. congolensis antigens.

In vitro and in vivo inhibition of Dermatophilus congolensis by coagulase-negative antibiotic-producing staphylococci from pigs

When tested on solid media the growth of 19 Dermatophilus congolensis strains was inhibited by antibiotic-producing staphylococci isolated from pigs. Two strains, D congolensis D11 and D15, which were very sensitive to the producers and caused lesions of dermatophilosis in a mouse model, were further used to investigate the ability of the producers to inhibit lesion formation by the strains of D congolensis. The simultaneous application of the antibiotic-producing staphylococci and D congolensis suppressed formation of the lesions in the mouse.

Quantification of keratinolytic activity from Dermatophilus congolensis

The bacterium Dermatophilus congolensis is the causative agent of pitted keratolysis, a skin disease. Infection occurs mainly in keratinized tissues and it is necessary for the organism to produce and excrete exoenzymes which are able to degrade keratin. We investigated the amount of keratinase liberated using Keratinazure as substrate and the fungal protease XI as standard. When compared with uninoculated samples, D. congolensis liberated significant amounts of keratinase during a 12-day incubation period with this substrate. An equivalent of 15 units of protease (keratinase) was produced by 10(7) colony-forming units of D. congolensis during a 12-day period at 37 degrees C. We consider the extracellular proteolytic activity of this bacterium to be responsible for keratinized tissues being the main sites of infection.

Evaluation of vaccines against ovine dermatophilosis

Intradermal vaccination of live crude filaments (vaccine A) was compared with a vaccine (vaccine B) consisting of a 45 kD zoospore protein and mucoid material coating filaments in its ability to protect sheep from experimental Dermatophilus congolensis infection. Fourteen and 21 days after challenge, vaccine A sheep had fewer lesions ( P<0.001) than the vaccine B sheep. The lesions on the vaccine A sheep were also less severe 14 and 21 days after challenge ( P<0.05, P<0.01 respectively). In a second study, vaccine A was assessed for its ability to protect against natural challenge. Ten weeks after contact with sheep with active and generalised dermatophilosis no difference was found between the number of lesions present on the vaccine A and unvaccinated sheep and no differences were found in the number of sheep in each group with active lesions.

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.

The effect of energy malnutrition in ruminants on experimental infection with dermatophilus congolensis

The ability of malnourished and optimally fed animals to resist infection with D. congolensis was assessed by the dose-response to experimental inoculation. The severity of infection, as measured by scoring the lesions, was the same in both groups of lambs. However marked differences were seen between the two groups in the appearance of scabs and in the time taken for them to resolve. The malnourished animals had more persistent, chronic lesions compared with the more obvious, acute type lesions seen on the skin of the healthy controls. These results were probably related to the reduced rates of wool growth and lanolin production found in the malnourished lambs, which may reflect a reduction in the rate of cellular turnover in the skin of these animals.

Natural Dermatophilus congolensis infection in camels ( Camelus dromedarius) from Kenya

Natural Dermatophilus congolensis infection is found in many species of livestock and wild animals. It is, however, rarely described in camels and there are no details of bacterial isolation. In an investigation of both arid and semi-arid areas in Kenya, an outbreak of dermatophilosis was observed in camel calves being reared on a commercial farm in a semi-arid area. Histopathology and bacterial isolation were used to diagnose the diseases. The potential impact of the disease in camels is discussed.

Inhibition of Dermatophilus congolensis by substances produced by bacteria found on the skin

Bacteria, isolated from the skins of clinically normal sheep, were tested for inhibitory activity against Dermatophilus congolensis grown in vitro. Out of 85 bacterial isolates, 19, mainly Bacillus spp., showed zones of inhibition when grown together with D. congolensis. The inhibitory activity was shown to be due to the metabolites released by the bacteria.

The effect of recent vaccination on the dose-response to experimental Dermatophilus congolensis infection in rabbits

Dermatophilus congolensis infection of rabbits was used to investigate the effects of active immunity on epidermal challenge following vaccination. Rabbits (three groups of four) were vaccinated intradermally with live whole-cell preparations of D. congolensis strains SS18C and FD11 (groups SSVAC and FDVAC respectively); a third group (UNVAC) remained as unvaccinated controls. Two weeks after vaccination, separate 1.5-cm2 clipped and ether-swabbed skin sites were inoculated with a 10-fold dilution range (10(7) to 10(1) zoospores per cm2 of skin) of SS18C or FD11. Lesion scores at each site were calculated from the sum of individual scores (0 to 4+) for erythema, oedema and scab formation multiplied by the percentage of the inoculated area affected. A clear dose-response relationship between the size of inoculum and the severity of lesions was seen for both D. congolensis stains in the control group (UNVAC). In the SSVAC and FDVAC groups the lesions were less severe and developed more quickly. The number of zoospores required to cause infection in the vaccinated animals was up to 10,000-fold higher for homologous inoculated sites and 100-fold for heterologous sites. Serological analysis was carried out with an ELISA system. Vaccination and challenge resulted in increases in specific antibody against D. congolensis antigens. Cross-reacting antibody to the heterologous strain of D. congolensis used was demonstrated in both vaccinated groups but did not correlate with equal protection to homologous or heterologous challenge. The dose-response relationship demonstrated by this model enabled semi-quantitative analysis of the effects of vaccination on D. congolensis infective dose and severity of infection.(ABSTRACT TRUNCATED AT 250 WORDS)