CASE NOTES

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Lumpy skin disease excluded and severe Dermatophilus infection diagnosed in a heifer weaner

Meg Parsons, District Veterinarian, Local Land Services, Northern Tablelands

Posted Flock and Herd August 2024

Summary

Dermatophilosis is a bacterial skin infection caused by Dermatophilus congolensis. For this bacterium to cause disease, skin damage and moisture are usually necessary. This case was unusual as it did not have these aspects present and was so severe in its presentation.

History

In April 2024 near Inverell in Northern New South Wales, a single heifer out of a mob of 60 head of Shorthorn cattle presented to their private veterinary practice for severe skin changes. Upon discussion with the client, Local Land Services was contacted and subsequently performed a property visit for the purposes of excluding Lumpy Skin Disease (LSD).

Two weeks prior to the property visit, the producer noticed skin lumps on the body of the affected heifer. These lesions continued to spread and significantly worsen. The heifer had been weaned one week before the consultation and, while still eating and drinking, had lost a significant amount of weight in comparison to her herd mates. The producer did not believe she had been itchy, she was defaecating normally, and was bright and alert. The heifer had not received any treatments.

No other cattle on the property had developed skin lesions. There were no adverse weather events, heavy rainfall, or long wet periods in the month prior. The weaners had no access to any supplements, minerals or hay prior to weaning. The cattle were grazed on primarily native pasture with a small amount of sub-tropical plant species sown down previously. There were no known toxic plants or forage crops, including lucerne, vetch and cowpeas. The dams were up to date with clostridial and leptospirosis vaccinations and had received Multi-min® injections. The property owner had not initiated a pestivirus control or vaccination program, raising questions about the possibility of the heifer being a persistently infected calf.

Clinical Examination

Upon examination the heifer was bright and alert. Up to 80% of her skin was covered with grey, crusted, raised, coalescing lesions. Removal of the superficial dermal layer and hair exposed raw, red skin underneath. There was no evidence of the characteristic purulent discharge under the scabs, often associated with Dermatophilus spp. Several areas appeared slightly necrotic where scabs had been previously removed. The heifer's skin condition was mildly pruritic but did not seem painful. There was no erythema, heat or discharge observed, which are clinical signs commonly associated with active infection. There were no lesions on the coronary bands or the mucous membranes, including the eyes, nose, tongue, gingiva, and vulva. The heifer had a fever of 40.7°C and had a body condition score of 2/5. The rest of her physical examination was within normal limits.

Lithium heparin, EDTA and plain blood samples, along with fresh and fixed scabs and biopsies were sent to Elizabeth Macarthur Agricultural Institute (EMAI).

Figure 1. Wet hair allowing for the distribution of skin masses over the hindquarter to be appreciated

Figure 2. Distribution of lesions along the backline

Figure 3. Skin lesions on the perineum, periorbital area and ear pinna

Diagnosis

LSD testing was negative. Histopathology showed diffuse, marked, chronic exudative, neutrophilic dermatitis and folliculitis, characterised with ulceration, hyperkeratosis, haemorrhage and filaments of gram-positive cocci bacteria (Chamings & Jordan, 2024). The histological changes and morphology of the bacteria was consistent with infection with the actinomycete Dermatophilus congolensis. A bacterial culture was then undertaken with profuse mixed growth including Dermatophilus congolensis (Chamings & Jordan, 2024).

The heifer was then tested for pestivirus to determine if she was a persistently infected animal. Testing was negative.

Treatment

The heifer was treated with topical chlorhexidine washes and a course of procaine penicillin at 15mg/kg as an intramuscular injection once daily for five days. Over a period of a month, the crusting and scabs fell off leaving hairless skin underneath. By the end of June 2024, all her hair had regrown.

Discussion

Dermatophilus congolensis are filamentous, branching, facultative anaerobic, gram-positive actinomycete bacteria (Parkinson, Vermunt & Malmo, 2010; Lee, Rogers & Hillbrich, 2019). Infection causes a superficial, exudative dermatitis that is commonly known as 'rain scald,' 'lumpy wool' or 'strawberry foot rot' (Moriello, 2019). It can affect many domestic species including cattle, sheep, goats, and horses. The bacteria may persist in healthy carrier animals and are not highly invasive (Read, 2011). Parkinson et al. indicated that it is "virtually impossible" to establish infection and lesions on skin that is intact and undamaged without moisture and skin abrasions (Smith, 2009; Parkinson, Vermunt & Malmo, 2010).

This severe presentation of dermatophilosis seems more commonplace overseas, however there have been reports of severe dermatitis cases in Australian cattle. (Read, 2011; Lee, Rogers & Hillbrich, 2019). Research in Australia has been predominantly focused around Dermatophilus spp. infection in sheep, with 'lumpy wool' or 'fleece rot' being significantly more common in Australia and having a production impact on wool enterprises (Parkinson, Vermunt & Malmo, 2010; Tellam et al., 2021).

Factors that impact its ability to colonise and result in clinical disease include weather conditions resulting in prolonged wetting of the animal and high temperature and humidity leading to further skin maceration (Moriello, 2019). Disruption of the integument by ectoparasites, particularly ticks in cattle, also influences the prevalence of disease (Ndhlovu & Masika, 2016; Tellam et al., 2021). Other sources of skin damage can include prickly vegetation or biting flies. Our case had no known external factors precipitating clinical disease.

Dermatophilosis may be seen in animals of all ages but is most prevalent in young animals, particularly if they are chronically exposed to moisture or are immunocompromised (Moriello, 2019). It is for this reason that pestivirus testing was undertaken on the affected heifer. Other causes of immunocompromise, such as mineral deficiencies, were not investigated due to the excellent health of the remaining mob of cattle.

While it is likely that the stress of weaning exacerbated the heifer’s disease, skin lesions were present and worsening prior to this event. It is uncommon to see Dermatophilus spp. infections this severe in the Northern Tablelands; they are predominantly seen in tropical or subtropical regions (Parkinson, Vermunt & Malmo, 2010). It is even more uncommon to see them in a relatively dry season with low pasture density and without prolonged periods of wetting. Cases like this one are a prime opportunity to rule out potentially serious exotic diseases including LSD.

References

1. Chamings A & Jordan A (2024) Laboratory Report; Final Report [PDF]. Department of Primary Industries, Elizabeth Macarthur Agricultural Institute
2. Lee E, Rogers J & Hillbrich E (2019) Dermatophilus and lice causing severe dermatitis in a heifer Flock & Herd www.flockandherd.net.au
3. Moriello KA (2019) Dermatophilosis in Animals MSD Manual Veterinary Manual www.msdvetmanual.com
4. Ndhlovu DN & Masika PJ (2016) Bovine dermatophilosis: Awareness, perceptions and attitudes in the small-holder sector of north-west Zimbabwe Onderstepoort Journal of Veterinary Research 83(1):a1004 doi.org
5. Parkinson TJ, Vermunt JJ & Malmo J (2010) Diseases of Cattle in Australasia. Vetlearn, Wellington
6. Read L (2011) Dermatophilosis in weaner cattle Flock & Herd www.flockandherd.net.au
7. Tellam RL, Vuocolo T, Denman S, Ingham A, Wijffels G, James PJ & Colditz, IG (2021) Dermatophilosis (lumpy wool) in sheep: a review of pathogenesis, aetiology, resistance and vaccines Animal Production Science 62(2):101-113 doi.org