By TVMDL, The Texas A&M Veterinary Medical Diagnostic Laboratory protects animal and human health through diagnostics. An agency of the Texas A&M University System, TVMDL comprises two full-service laboratories, in College Station and Amarillo, and two poultry laboratories, in Center and Gonzales
Photosensitization
Photosensitization occurs when non-pigmented or lightly pigmented skin is more susceptible to UV light due to photodynamic molecules within the dermis. Severe skin damage can result and include ulceration, necrosis and edema.
Causes
Type 1 (Primary): Ingestion of preformed photodynamic toxins (i.e. hypericin in St. John’s Wort, drugs: phenothiazine, tetracycline)
Type 2 (Aberrant Pigment Metabolism): Congenital defective pigment synthesis causing abnormal accumulations of photodynamic agents in the tissues (uroporphyrin I, coproporphyrin I, protoporphyrin III)
Type 3 (Hepatogenous): Most common form; Impaired capacity of the liver to excrete phylloerythrin, a photodynamic agent, secondary to hepatocellular damage or bile duct obstruction
Toxic Plants
Primary photosensitization:
- Bishop’s weed (Ammi majus) furocoumarin
- Rainlily (Cooperia pedunculata) fungal elaboration
- Dutchman’s breeches (Thamnosma texana) psoralens
Hepatogenous photosensitization :
- Moldy Bermudagrass (Cynodon dactylon) fungal elaboration
- Lantana (Lantana camara) lantadene A and B
- Sacahuista, blooms only (Nolina texana) saponins
- Kleingrass (Panicum coloratum) saponins
- Puncturevine (Tribulus terrestris) saponins
Lesions
- Main lesions include and are not limited to skin necrosis and ulceration of the non-pigmented skin, white areas along the back, face, sides of udders, muzzle, underside of tongue, lips, eyelids, and ears. Differences in distribution are related to differences in skin pigmentation of breeds and individual animals
- Affected skin will be red, oozing fluid, and swollen
- In severe cases, large crusts of necrotic, black skin may slough off
- Affected animals may also be icteric with yellow discoloration of the skin and mucus membranes
- Animals will be shade-seeking
Diagnosis
- Clinical signs
- Exposure to agents, primary or hepatotoxic, and presence of characteristic lesions
- Bloodwork: increased sorbitol dehydrogenase, gamma glutamyltransferase, alkaline phosphatase enzymatic activity and total bilirubin
TVMDL recommends submitting samples for the following tests. In the case of photosensitization, rumen microscopy is of limited use.
- Ruminant Chemistry Profile
- Liver biopsy for Histopathology
- Plant ID
Information on sample shipment can be found at tvmdl.tamu.edu. Contact the laboratory with questions.
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