Dermatophilosis of sheep association with dipping and effects on production

Dermatophilosis (lumpy wool) in sheep: a review of pathogenesis, aetiology, resistance and vaccines

Lumpy wool (dermatophilosis) develops following prolonged wetting of sheep when bacterial proliferation in wool and on skin induce an exudative dermatitis, causing a superficial skin lesion and damage to wool follicles and fibres. The incidence of dermatophilosis is strongly dependent on wet and warm weather and, hence, infection is sporadic. While older animals are less at risk than are lambs, it is unclear whether this reflects naturally acquired immune resistance or the maturation of skin and wool fibres. Dermatophilosis directly causes wool production losses and it also is a risk factor for blowfly strike, which has a substantial economic impact and increasing challenges associated with current control procedures. This review assessed research on the bacterial causes of lumpy wool, the characteristics of the resulting immune defence reactions in sheep, current control strategies, and limitations of previous attempts to control lumpy wool by sheep vaccination.

Fleece rot and dermatophilosis (lumpy wool) in sheep: opportunities and challenges for new vaccines

During prolonged wetting of the fleece, proliferation of bacterial flora often dominated by Pseudomonas aeruginosa or Dermatophilus congolensis can induce dermatitis and fleece damage termed fleece rot and dermatophilosis respectively, which predispose sheep to blowfly strike. A large research effort in the 1980s and 1990s on vaccines to control fleece rot and dermatophilosis met with limited success. This review examines theoretical and technological advances in microbial ecology, pathogenesis, immunology, vaccine development and the characterisation of microbial virulence factors that create new opportunities for development of vaccines against these diseases. Genomic technologies have now created new opportunities for examining microbial dynamics and pathogen virulence in dermatitis. An effective vaccine requires the combination of appropriate antigens with an adjuvant that elicits a protective immune response that ideally provides long-lasting protection in the field. A clinical goal informed by epidemiological, economic and animal welfare values is needed as a measure of vaccine efficacy. Due to dependence of fleece rot and dermatophilosis on sporadic wet conditions for their expression, vaccine development would be expedited by in vitro correlates of immune protection. The efficacy of vaccines is influenced by genetic and phenotypic characteristics of the animal. Advances in understanding vaccine responsiveness, immune defence in skin and immune competence in sheep should also inform any renewed efforts to develop new fleece rot and dermatophilosis vaccines. The commercial imperatives for new vaccines are likely to continue to increase as the animal welfare expectations of society intensify and reliance on pharmacotherapeutics decrease due to chemical resistance, market pressures and societal influences. Vaccines should be considered part of an integrated disease control strategy, in combination with genetic selection for general immune competence and resistance to specific diseases, as well as management practices that minimise stress and opportunities for disease transmission. The strategy could help preserve the efficacy of pharmacotherapeutics as tactical interventions to alleviate compromised welfare when adverse environmental conditions lead to a break down in integrated strategic disease control. P. aeruginosa and D. congolensis are formidable pathogens and development of effective vaccines remains a substantial challenge.

Ovine dermatophilosis in young sheep associated with the grazing ofBrassicaspp. crops

The occurrence of dermatophilosis in five month old lambs associated with the grazing of Brassica spp. crops is reported on four farms. The prevalence of the disease varied from 3% to 45% within affected flocks. An additional finding was the occurrence of nervous signs in a small number of more severely affected lambs, characterised by a sudden lowering of the hindquarters. The association between dermatophilosis and the grazing of Brassica spp. crops is discussed.

Difference between lambs with chronic and mild dermatophilosis in frequency of alleles of CD3 gamma

Southern blots prepared with DNA from 20 Merino lambs that previously had chronic dermatophilosis (chronic) and 20 lambs that previously had mild dermatophilosis lesions (resistant) were hybridised with DNA sequences of the genes for the T-cell receptor-beta (TCR beta), a TCR-associated peptide 'cluster designation 3 gamma chain' (CD3 gamma) and ovine Major Histocompatibility Complex class 1 (ov. MHC class 1). There was a significant difference in the incidence of an allele of CD3 gamma between the chronic and resistant lambs. No significant difference in the incidence of alleles of TCR beta or ov. MHC class 1 was detected.

Isolation of Dermatophilus congolensis phage from the 'lumpy wool' of sheep in Western Australia

A lytic phage with species-specific activity was isolated from wool samples infected with the actinomycete Dermatophilus congolensis, the agent of 'lumpy wool', collected from properties in Western Australia. The physiochemical properties, plaque morphology, host range and particle morphology of the phage isolated were characterized. The isolated phage reduced the cell numbers of Dermatophilus congolensis on infected wool samples in vitro. It may therefore have potential as a biocontrol agent of dermatophilosis.

Skin diseases in a Merino sheep herd related to an excessively rainy winter in a Mediterranean climatic zone

A retrospective study is presented here in which an outbreak of dermatophilosis and morbidity of fleece rot in a sheep herd grazing throughout the year in the Carmel hills are described for the first time in a Mediterranean climatic zone. Both diseases were closely related to intense and prolonged rains during the winter months of 1991/1992. Morbidity of dermatophilosis appeared after 650 mm and that of fleece rot after 1320 mm of precipitation. The pathogenesis of these diseases is discussed.

Genetic analysis of dermatophilus spp. using multilocus enzyme electrophoresis

Multilocus enzyme electrophoresis was used to examine a collection of 41 mainly Australian isolates of Dermatophilus congolensis that had been cultured from sheep, cattle, horses, a goat, a marsupial and Chelonids. Allelic variation was examined at 16 enzyme loci. The isolates were divided into eight distinct electrophoretic types (ETs) with a mean genetic diversity per locus of 0.41. The three isolates from Chelonids represented a distinct clone in ET 1 which was separated from the remaining cluster of isolates of D. congolensis by a genetic distance of 0.852. These findings supported a previous proposal that the isolates from Chelonids represent a new species of Dermatophilus. The other 38 D. congolensis isolates were separated into two divisions (I and II) by a genetic distance of 0.560. The divisions were both subdivided into groups that either only contained alpha-hemolytic or beta-hemolytic isolates, but all isolates in each ET had only one hemolytic pattern. Isolates originating from the same animal species, or from the same geographic location, were not all closely related genetically. The allocation of isolates into ETs correlated well with their distribution into DNA restriction endonuclease analysis patterns previously established for the collection. Although relatively few distinct strains of D. congolensis were identified amongst the collection, significant genetic diversity existed within this population.

Variation in cultural, morphological, biochemical properties and infectivity of Australian isolates of Dermatophilus congolensis

Recent vaccination studies with Dermatophilus congolensis showed that variation of challenge strains had a considerable influence on protection afforded by the vaccines. In this study cultural, morphological and biochemical properties of 30 D. congolensis isolates from throughout Australian were investigated. The infective dose required to produce lesions of equivalent severity by these isolates for sheep, rabbits and guinea pigs was also examined and the isolates were grouped into four clusters of similar infectivity ranking. Analysis of the relationship between cultural, morphological and biochemical characteristics and infectivity rankings of clusters was undertaken to determine if certain properties were linked to infectivity. Considerable variability was found in haemolytic activity on blood agar, mucoid nature of colonies, motility, flagella density and polarity, capsule width, restriction enzyme profiles of bacterial DNA, protein electropherotype, carbohydrate content, and enzymic activity against proteins, maltose, chondroitin-4-sulphate, phospholipids and lipids. Of these properties haemolytic activity and enzyme activity against casein, chondroitin-4-sulphate and lipids showed some link with infectivity ranking for these isolates.

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 levels 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.

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 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.

Inflammatory cell and immune function in Merino sheep with chronic dermatophilosis

Components of inflammatory and immunological responses were compared in 17 Merino sheep with chronic dermatophilosis (Group 1) and 15 Merino sheep that had recovered from the disease (Group 2). The functions studied included: (i) total and differential white cell counts; (ii) phagocytic function and intracellular killing by neutrophils; (iii) humoral immune response to T-dependent and T-independent antigens and to Dermatophilus congolensis. (iv) lymphocyte blastogenic responses to phytohaemagglutinin; (v) bovine serum albumen and D. congolensis antigens; (vi) quantification of T-lymphocyte subsets in skin lesions resulting after re-infection with D. congolensis zoospores. After all lesions were treated and the sheep were shorn, both groups of sheep were re-infected with D. congolensis. Both groups had similar infection rate, severity of lesions and rate of resolution after re-infection. The Group 2 sheep had significantly higher primary and secondary antibody responses to killed Brucella abortus cells than Group 1 sheep, but Group 1 sheep had higher levels of specific D. congolensis antibody throughout the trial. Neutrophils from Group 1 sheep showed a higher phagocytic rate for D. congolensis zoospores than Group 2 sheep when the zoospores were opsonised by sera from the Group 1 sheep, but there was no difference in their ability to kill ingested zoospores. Although there were some differences between the groups in the proportion of lymphocytes in lesions that reacted with monoclonal antibodies to T4, T8 and T19-19 lymphocyte markers at various times after re-infection, the sheep in Group 2 consistently had higher levels of lymphocytes reacting to a monoclonal antibody for the T6 lymphocyte antigen in skin biopsies collected 9, 15 and 21 days post-inoculation (p.i.) than did sheep in Group 1. Group 2 sheep also had higher levels of epidermal cells with immunohistochemical properties of Langerhans cells at lesion sites 15 and 21 days p.i.

Vaccination against ovine dermatophilosis

Zoospore, filamentous and soluble antigens were prepared from Dermatophilus congolensis and examined for their ability to protect sheep from challenge with D. congolensis zoospores. In 1 experiment, sheep were vaccinated with Antigens A, B and C. The number of sheep protected in the group vaccinated with Antigen B was greater (P less than 0.05) than that in the unvaccinated group after challenge. The group vaccinated with Antigen B had a higher antibody response (P less than 0.05) to Antigen B than to Antigen A or C. In a second experiment, 2 groups of sheep were vaccinated with Antigen B. All sheep in this study developed lesions after challenge, but those on the vaccinated sheep were less severe (P less than 0.05) than those on the unvaccinated sheep. The antibody response to Antigen A, 28 days after vaccination, was higher (P less than 0.05) than the response to Antigen B.

A survey of ovine dermatophilosis in Western Australia

A random sample of 200 Merino sheep owners was interviewed by telephone during April 1983 and asked questions relating to the prevalence of ovine dermatophilosis in their flocks, methods used for prevention and treatment of dermatophilosis, management strategies employed and the location and annual rainfall of each farm. The response rate was 99.5%. During the previous 12 months 62.3% of farmers had observed dermatophilosis in their flocks. The prevalence within flocks was highest in hoggets (mean 2.2%, range 0 to 75%) followed by lambs (mean 0.8%, range 0 to 25%), ewes (mean 0.6%, range 0 to 20%) and wethers (0.2%, range 0 to 20%). The mean weight of wool identified as affected by dermatophilosis was 58 kg (range 0 to 882 kg). Preventive measures were used on 57% of farms and the most common methods were changes in dipping practice (23.6%) and culling of affected sheep (21%). An average of 13.7 sheep per farm were culled for dermatophilosis and of these, 82% were sold and the remainder (18%) were killed on the farm. Antibiotics, of which most were combinations of penicillin and streptomycin were used to treat dermatophilosis on 8.5% of farms and treatments other than antibiotics were used on 10% of farms. The prevalence of dermatophilosis and its relationship to various environmental and management factors varied with the age and sex of sheep. Discriminant analysis indicated that of the factors studied, average annual rainfall, month of lambing, average fibre diameter and the month ewes were shorn were related to the prevalence of dermatophilosis in lambs.(ABSTRACT TRUNCATED AT 250 WORDS)