A Menagerie of Zoonotic Diseases

Acute Retinal Lesion From Toxoplasmosis An 18-year-old woman presented with diminished vision and recent onset of floaters in the right eye. Her medical and ocular histories were noncontributory. An ophthalmologic examination revealed mildly decreased visual acuity in the right eye. There was no iritis, but dilated fundus evaluation indicated a vitritis—an area of retinal yellowish whitening with elevation and adjacent retinal vein inflammation. The retinal and vitreous changes were diagnosed as toxoplasmic retinochoroiditis. Unilateral and solitary ocular lesions that display little pigment deposition result from acute acquired toxoplasmosis, whereas congenital ocular toxoplasmosis is usually bilateral. Most ocular lesions are located in the posterior pole, particularly in the macular region. Ocular toxoplasmosis typically involves the inner retina and is associated with a marked vitreous reaction. As many as one quarter of all posterior uveitis cases may be attributed to toxoplasmosis. Acute lesions are yellowish white, elevated patches with blurred borders. They may heal spontaneously after several weeks or months and produce a well-demarcated chorioretinal scar with bare sclera often surrounded by hypertrophic retinal pigment epithelium. Reactivated disease may provoke the appearance of satellite lesions next to old scars. Toxoplasmosis is caused by the protozoon Toxoplasma gondii, which infects both humans and animals. The common routes of transmission to humans are ingestion of contaminated food or undercooked meat, inhalation of the oocysts of the parasite shed in cat stool, and intrauterine infection to the fetus of an infected mother. This patient denied eating raw meat but did keep several cats as pets. Treatment of ocular toxoplasmosis is only indicated if the patient’s vision is adversely affected or if the lesion is threatening the optic nerve or macula. Any of a number of antitoxoplasmic agents may be prescribed, including pyrimethamine, sulfadiazine, clindamycin, tetracycline, and trimethoprim-sulfamethoxazole (TMP-SMX). Significant inflammation is treated with oral prednisone in conjunction with antimicrobial therapy. This patient’s infection responded to treatment with clindamycin, TMP-SMX, and prednisone. ___________________________________________________________________________________________________________ Orf A 32-year-old man who had no significant medical history complained of “something growing on the knuckles of my right hand.” He reported that a “bump” was forming on the site of a cut he sustained while slaughtering sheep 3 weeks earlier. There was no blister, discharge, or pain. The patient denied any fever, cough, or malaise. He also did not recall seeing any lesions or bumps on the sheep. The lesion was a solitary, well-defined, erythematous nodule that measured 1 cm in diameter and 0.6 cm in height, with a papillomatous surface. There was no lymphadenopathy or swelling of the involved metacarpal. Cultures were negative for acid-fast bacilli and anaerobic organisms; a culture for aerobes yielded Citrobacter koseri that was sensitive to ciprofloxacin. The findings of a shave biopsy and the history were consistent with a diagnosis of orf, also called ecthyma contagiosum and contagious pustular dermatosis. The orf virus, a DNA Parapoxvirus, is endemic among sheep and goats and the products of these animals. Infected animals usually show a vesicular or papular eruption on the feet, lips, udders, and oral mucosa. Humans acquire the disease by direct contact with infected animals or contaminated objects, such as fences and door frames. The virus has been known to remain infective for more than 15 years at room temperature and more than 20 years when refrigerated. It is a common occupational disease among meat industry employees who deal with sheep; reinfection occurs fairly frequently in these workers. A solitary papule at the site of initial contact usually appears after an incubation period of less than 4 weeks. The typically benign lesion progresses through 6 distinct stages—maculopapular, target, acute, nodular, papillomatous (Figure), and regressive—and heals spontaneously within 4 to 24 weeks. The lesion may be misdiagnosed as a keratoacanthoma or pyogenic granuloma; in the nodular stage, it can resemble a giant molluscum contagiosum. Complications occur rarely; they include lymphangitis, lymphadenitis, chills and fever and, as seen in this patient, secondary bacterial infections. There is no specific antiviral therapy for orf. Antibiotics may be used when the presence of secondary bacterial infection has been proved. This patient completed a course of ciprofloxacin, and the lesion resolved. ______________________________________________________________________________________________________ Catscratch Disease This 12-year-old girl had a persistent, nontender enlarged lymph node in the right groin. After the lymphadenopathy had failed to respond to antibiotic therapy, pathologic examination of the lymph node established the diagnosis of catscratch disease. The child remembered that she had been scratched on the right calf by a cat the month before; the scratch had already healed when the lymph node appeared. This child had no symptoms other than lymph node enlargement; however, systemic symptoms of fever, malaise, and headache may occur 2 to 3 weeks after a cat scratch. Spontaneous node regression usually occurs within 4 weeks. ________________________________________________________________________________________________________ Tularemia A 25-year-old itinerant construction worker sought medical care because of flu-like symptoms and a painful inguinal lymph node on his right side. The node was 3 times its normal size and exquisitely tender. The patient claimed he had no symptoms of venereal disease and no problems with his right leg or the right side of his body. Because he was uncooperative and refused further examination, he was given penicillin C, 1,200,000 U IM, and a prescription for double-strength trimethoprim-sulfamethoxazole. The patient returned the next day because the node had become even more painful. His temperature was 38.4ºC (101.2ºF). This time, the examination was completed with cooperation from the patient. A second, smaller node in the same inguinal chain and an infected 3-cm laceration on the lateral aspect of the patient’s right leg were discovered. On questioning, the patient’s story emerged: he had gone hunting the previous week, although he thought he had cut his leg sometime before then. He had killed 2 jackrabbits and 2 cottontails, thrown them into a sack, and tossed it over his shoulder. He later noticed that blood from the rabbits had leaked out of the sack and down his leg, seeping through a hole in his jeans into the leg wound. The rabbit was suspected to be infected with Francisella tularensis, and the suspicion that the patient had tularemia was confirmed by bacteriologic identification from a biopsy of the node in the groin. On the recommendation of an epidemiologist, a 10-day course of streptomycin was given, 1 g IM twice daily. Five days later, recurring fever mandated a second, 6-day course of the antibiotic. The patient was lost to follow-up.