Hortaea werneckii: A Possible Cause of PIX Skin Disease in the American Alligator (Alligator mississippiensis)
IAAAM Archive
Heather Dickson1; Paul Cardeilhac1; Rolf Larsen1; J. Don Ashley2
1College of Veterinary Medicine, University of Florida Gainesville, FL, USA; 2Ashley Associates INC, Tallahasse, FL, USA


Unusual skin lesions on alligator hides, designated "PIX" scars by the tannery, have been seen in Florida and Louisiana since November of 1999.1 The scars appear as small lesions usually about 1mm in diameter and located primarily in the ventral neck, abdomen and tail region. These lesions have been seen on fresh, salted and tanned hides. The animals do not show obvious clinical signs but the seriousness of the problem arises when the hides are sent to the tanner for grading, where infected hides may be severely downgraded by 50% or even branded as total rejects (no value). The incidence of serious lesions has been noted to be as high as 75% in a lot of 105 hides. Blood cultures from captive animals with typical lesions were made and examined for the presence of aerobic microorganisms and fungi; however, no growth could be detected after 48 hours. Serum chemistry values and electrophoresis patterns were considered normal. Biopsies were made of typical lesions which were embedded in paraffin blocks, cut, made into slides and stained using PAS and H&E. The lesion was considered to be a granuloma and the outer layer (stratum corneum) and the scale area above the granuloma was disrupted. The granuloma was observed to contain rod-shaped structures tentatively identified as hyphae with the use of fluorescent and confocal microscopy. A GMS stain (Grocott's Method for Fungi) was performed on a section from the lesion and the section was considered positive for the presence of hyphae inside the granuloma. Biopsies were then taken from fresh unsalted hides containing pix-like lesions. Two lesions per hide were obtained and one lesion was cultured on fungus-selective media (Sabouraud Dextrose and Mycobiotic). The comparison lesion was prepared as described above for histological examination. The only fungus that grew on the fungal-selective media was identified as Hortaea werneckii by the Fungus Testing Laboratory University of Texas Health Science Center, San Antonio Texas. This organism is known to cause superficial, asymptomatic infections of the stratum corneum in man (tinea nigra) and animals. In alligators, the granuloma requires about 12-24 months to erupt. The increase in size of the granuloma causes rupturing of the stratum corneum to form the PIX pit or scar. The size of the granuloma may ultimately depend on the number of fungal spores that initiated the infection and their ability to grow within the lesion. The size of inoculum or number of spores causing infection probably depends on the number of spores in the environment of the alligator, while the ability for the fungus to grow may depend on the immune status of the alligator. There is a need for effective diagnostic procedures to detect the disease as well as methods to identify, contain, monitor, and treat.


Mr. Wayne T. McClellan and Mr. Joseph P. Cardeilhac provided technical assistance. The authors wish to thank Dr. Ruth Elsey and Mr. Noel Kindler and for their valuable contributions to this project. This project was supported by a grant from the Louisiana Dept. of Wildlife and Fisheries Fur & Alligator Advisory Council


1.  Dickson HM, Cardeilhac PT. PIX: A New Skin Disease of Alligators. Abstracts from the 53rd Meeting Animal Disease Research Workers of the Southern States. Feb. 10-12, 2001. Abstract 10.

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Heather Dickson

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