In vitro studies of Dermatophilus congolensis antimicrobial susceptibility by determining minimal inhibitory and bacteriocidal concentrations

Postural and gait abnormalities in a group of Romney lambs due to pain induced by severe chronic cutaneous dermatophilosis

CASE HISTORY

Fifteen lambs from a flock of 1,000, 5-month-old Romney lambs in the Manawatū region of New Zealand, developed unusual postural and gait abnormalities during the summer of 2020. In mid-January, the lambs were grazing a raphanobrassica crop (xRaphanobrassica; Brassica oleracea x Raphanus sativus) but were removed from this crop soon after as they developed dermal lesions on the pinnae consistent with photosensitisation (colloquially known as "rape scald"). The lambs were placed onto a shaded paddock containing a pasture of predominantly perennial ryegrass (Lolium perenne) and white clover (Trifolium repens). One week following removal from the crop (late January), the 15 lambs developed abnormal postures and gaits that were described by farm staff as "neurological" and "swayback-like".

CLINICAL FINDINGS

From a distance, all 15 lambs exhibited remarkably similar abnormal posture and gait whereby their weight was borne on their carpi, and they appeared to crawl while walking due to crouched hindquarters and prominent lordosis. Of the affected lambs, five were submitted for clinical examination. All five had normal vital signs. The results of neurological examinations were within normal limits. In response to palpation of the dorsum, the lambs performed an exaggerated and unusual dipping motion, particularly when pressure was applied over the lumbar spine. Parting of the fleece over the dorsum revealed thickened, indurated skin that cracked and tore easily.

PATHOLOGICAL FINDINGS

The shorn pelt of a euthanised lamb revealed a large (100 cm × 40 cm), locally extensive, irregular ovoid region of the skin of the dorsum that was markedly thickened, indurated and crusted. Impression smears of the lesions revealed long filamentous chains of plump coccoid bacteria separated by transverse and longitudinal septa, consistent with Dermatophilus congolensis. Histopathology of the lesions revealed severe, chronic-active, locally extensive, necrosuppurative dermatitis with marked acanthosis, orthokeratotic and parakeratotic hyperkeratosis, ulceration, filamentous bacteria and coccoid zoospores.

DIAGNOSIS

Cutaneous dermatophilosis due to Dermatophilus congolensis.

CLINICAL RELEVANCE

Painful dermal lesions due to severe dermatophilosis of the dorsal skin of sheep are capable of causing postural and gait abnormalities that may be misinterpreted as signs of neurological abnormality. Such dermal lesions may be concealed by an apparently normal fleece.

Identification and Antimicrobial Resistance of Dermatophilus congolensis from Cattle in Saint Kitts and Nevis

Dermatophilosis is a form of dermatitis caused by the bacterium Dermatophilus congolensis. The disease usually presents as localized purulent dermatitis, crusty hair masses or widespread matting of the hair. This condition is most common in domestic ruminants; but it can also affect other wild animals and humans. Antimicrobial therapy is used in many regions to treat clinical dermatophilosis with varying results. In this study, we aimed to assess the antimicrobial susceptibility of D. congolensis isolates. Fifty-two isolates were obtained from animals showing clinical signs of the disease at farms in St. Kitts. The isolates were then confirmed as D. congolensis by phenotypic tests, PCR and MALDI-TOF Mass Spectrometry. Furthermore, minimum inhibitory concentrations (MIC) of 16 antimicrobial agents were determined, using the broth microdilution method. Although most antimicrobials showed MICs in line with published values, the tetracycline results displayed a clear bimodal distribution over the tested range, with most isolates showing low MICs and 6 isolates much higher values (+/− 100-fold increase). These results indicate the presence of acquired tetracycline resistance in D. congolensis on the island of St. Kitts. Whether the current observation has implications for efficacy of treating the disease must be confirmed in further research.

Comprehensive Molecular Dissection of Dermatophilus congolensis Genome and First Observation of tet(Z) Tetracycline Resistance

Dermatophilus congolensis is a bacterial pathogen mostly of ruminant livestock in the tropics/subtropics and certain temperate climate areas. It causes dermatophilosis, a skin disease that threatens food security by lowering animal productivity and compromising animal health and welfare. Since it is a prevalent infection in ruminants, dermatophilosis warrants more research. There is limited understanding of its pathogenicity, and as such, there is no registered vaccine against D. congolensis. To better understanding the genomics of D. congolensis, the primary aim of this work was to investigate this bacterium using whole-genome sequencing and bioinformatic analysis. D. congolensis is a high GC member of the Actinobacteria and encodes approximately 2527 genes. It has an open pan-genome, contains many potential virulence factors, secondary metabolites and encodes at least 23 housekeeping genes associated with antimicrobial susceptibility mechanisms and some isolates have an acquired antimicrobial resistance gene. Our isolates contain a single CRISPR array Cas type IE with classical 8 Cas genes. Although the isolates originate from the same geographical location there is some genomic diversity among them. In conclusion, we present the first detailed genomic study on D. congolensis, including the first observation of tet(Z), a tetracycline resistance-conferring gene.

Livestock pathology in the central African region: some epidemiological considerations and control strategies

Disease consistently features among the major constraints of livestock production in the central African region, orchestrating important economic losses. This article reviews livestock diseases of economic importance, including foot-and-mouth disease, trypanosomosis and dermatophilosis in cattle, peste des petits ruminants and gastrointestinal helminthosis in sheep and goats, and Newcastle disease in poultry. Some aspects of epidemiology such as pathogen identification, prevalence and risk factors are examined in the light of research findings in the region. Control tools such as vaccines, chemotherapeutic or prophylactic agents, and protocols developed for their efficient use are also reviewed. Constraints to the effective use of these tools have been identified as mostly due to institutional insufficiencies and measures for improvement have been proposed. These include the promotion of private professional veterinary services endowed with greater responsibility in animal health care, creation and promotion of community-based animal health care units in areas of marginal professional coverage, and adoption of a regional approach to the control of diseases of economic importance.

Prevalence of bovine dermatophilosis in a tropical highland region of Ethiopia

A study was made of bovine dermatophilosis on 540 animals at a high altitude (2400-2500 m above sea level) in Ethiopia. Eighty-two (15.4%) of the animals were affected by the disease which was more prevalent in local animals than was previously assumed. There was a significant (p < 0.05) difference in the prevalence among different age groups. However, the difference in the prevalence of the disease between males and females was not significant (p > 0.05). Associated risk factors included the relatively high average annual rainfall and humidity, tick infestation (76%) and management, related to the mixed crop-livestock production system. The possible impact of the disease on Ethiopian agriculture is indicated.

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.