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An uncommon fungal infection from farm animals

Introduction

Trichophyton verrucosum is a cosmopolitan zoophilic dermatophyte. The normal host for this organism is cattle and occasionally horses. Human infection is acquired through direct contact with these animals or contaminated fomites, usually following minor trauma to the skin.

Figure 1. Case 4 developed lesion after contact with beef cattle

Aim

To review cases of T. verrucosum infection diagnosed over a five year period.

Method

The Sullivan Nicolaides Pathology data base from 2009 – 2014 was searched for isolates of T. verrucosum.

The laboratory services Queensland and extends into New South Wales as far south as Coffs Harbour.

Results

Seven cases of T. verrucosum over a five year period time frame that identified more than 12,500 dermatophyte infections in total.

The most recent case (7) was a 54-year-old retired meat worker who owns a small property with one beef and three dairy calves all of which suffered from fungal infection. After clearing lantana and sustaining multiple scratches he developed a non-healing inflammatory lesion on his forearm which healed after three weeks of oral griseofulvin with some residual scarring.

Biopsy, bacterial and fungal cultures all demonstrated fungal infection and cultures grew T. verrucosum. Scrapings collected from his infected cattle also demonstrated large spore ectothrix infection and grew this dermatophyte.

Cases included six males and one female (Table 1). The age ranged from 27–71, mean 45 years.

All except one (Case 5) had association with cattle with one also with horses. The site of infection was the forearm (5) (figure 1), leg (1) and face (1). Case 6 developed her leg lesion after birdwatching and camping on a cattle property although did not have direct contact with cattle.

Three patients underwent skin biopsy and histology and in only one was hyphae seen on tissue sections.

Four of five bacterial cultures also grew T. verrucosum on bacterial agar. Unlike other dermatophytes growth is enhanced at 37OC. The cases were concentrated in SE Queensland and Northern NSW.

Four of the cases required systemic antifungal therapy to clear and a number were treated with several courses of antibiotics prior to the diagnosis being established.

Case No. Location Sex/Age Site Fungal Microscopy Contact Treatment
1 Kyogle, NSW M/32 Forearm No hyphae Cattle Bifonazole T
2 Avondale, NSW M/64 Forearm Hyphae 1+ Cattle/horses Terbinafine
3 Clarenza, NSW M/27 Forearm No hyphae Cattle No treatment
4 Charleville, Qld M/35 Forearm No hyphae Cattle Ketaconazole T
5 Boonah, Qld F/71 Lower leg Hyphae 1+ Cattle property Ketoconazole O
6 Kingstown, NSW M/29 Face Hyphae 1+ Cattle Griseofulvin O
7 Buccan, Qld M/54 Forearm Hyphae 1+ Cattle Griseofulvin O

Table 1: Culture positive cases T. verrucosum infection SNP 2009-2014

Conclusion

  1. verrucosum is an unusual zoonotic infection of the skin causing a highly inflammatory response involving the scalp, beard or exposed areas of the body in contact with cattle and horses.

Fluorescence under Wood’s ultra-violet light has been noted in cattle but not in humans.

Unlike other dermatophytes, growth is enhanced at 37OC.

Systemic therapy is usually required to clear the infection which is frequently mistaken for an inflammatory bacterial infection, initially being treated with antibiotics.

Advice on clearing the infection from animals was seen as important.

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General Practice Pathology is a regular column each authored by an Australian expert pathologist on a topic of particular relevance and interest to practising GPs. The authors provide this editorial free of charge as part of an educational initiative developed and coordinated by Sonic Pathology.