A Case Study of Photosensitivity Associated with Anaplasma spp. Infection in Cattle

SIMPLE SUMMARY: A five-year-old Holstein cow in her fifth month of gestation was presented to our ruminant livestock clinic for skin injury diagnosis, which occurred after grazing with other healthy Holstein cows for several months on a grass pasture. The cow was dewormed on a regular schedule and produced a decreasing amount of milk. It was RT-PCR positive to Anaplasma spp. infection. After starting oxytetracycline treatment, its condition improved within 24 h, and it fully recovered within 30 days. The underlying pathogenic mechanism of Anaplasma spp. infection is its impairment of the bile flow and liver function, leading to secondary photosensitization due to the pathological retention of phylloerythrin. In this case, Anaplasma spp should be considered an etiologic diagnosis of hepatogenous photosensitization, as the cow was continually exposed to sunlight while grazing on pasture. ABSTRACT: Anaplasma infection has not previously been reported as a cause of photosensitization. This case presents a five-year-old Holstein cow in her fifth month of gestation with skin injury of nonpigmented areas clearly delimited from adjacent unaffected pigmented skin. Specific lesions included alopecia, localized oedema, desquamation erythema, serous exudation, thick detached skin, fissures, crusting, and necrosis, indicating photodermatitis. Hematological abnormalities were leukocytosis with neutrophilia and normocytic hypochromic anemia. Based on a hemoparasitic examination of blood smears, the organism Anaplasma spp. was observed within the red blood cells. Biochemical analyses revealed increased serum liver enzyme activity associated with hepatocellular damage and cholestasis. This cow was RT-PCR positive for Anaplasma spp. infection. After treatment with oxytetracycline started, its condition improved within 24 h, and it recovered completely within 30 days. In this case, the underlying pathogenic mechanism of Anaplasma spp. infection facilitated the impairment of bile flow and liver function, resulting in hepatogenous photosensitization.