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Mohammadi, 1)VM, DvSc, Department of Clinical Sciences, School of Veterinary Medicine, Ferdowsi University of Mashhad, PO Box 91775- 1793, Mashhad, Iran A. Khodakaram Tafti, DVM, PhD), Department of Pathobiology, School of Veterinary Medicine, Shiraz University, PO Box 71345-1731, Shiraz, Iran INFESTATIONS of at least 60 species of ticks belonging to 10 genera cause paralysis in animals (Gothe and Neitz 1991). Dermacentor andersoni and Dermacentor variabilis in North America and Ixodes species, especially Ixodes holocyclus, in Australia, have been identified most frequently as causative agents (Malik and Farrow 1991). Karoo tick paralysis in South Africa primarily affects sheep in the distribution area of the tick Ixodes rubicundus (Spickett and Heyne 1988, Fourie and others 1989). Ornithodoros lahorensis is reported to cause tick paralysis in sheep in central Asia (Radostits and others 2000), and has been reported as the main cause of tick paralysis in Turkmenistan (Mamedkulov 1993). This short communication describes an outbreak of tick paralysis in a nomadic sheep flock in Iran, during a relatively mild and humid winter. In January 1999, the owner of the flock decided to spend the rest of the winter in a village near Shiraz (29°00'N, 49°00'E), the capital of Fars province, an agricultural lowland at an elevation of 1486 m. The animals shared a corn silage silo as part of a supplement to range grazing with three other neighbouring rural sheep flocks. The flock consisted of 400 sheep, and most of the ewes were in the last two months of pregnancy, with an appropriate history of vaccination and deworming programmes. During a general and physical examination of the flock, gradually ascending posterior paralysis, dropped lower lips, sternal recumbency with an inability to raise the head from the ground and, finally, lateral recumbency were observed. The animals showed a great desire to feed and drink, but were unable to prehend or drink (Fig 1). The menace, palpebral and corneal and pupillary light reflexes were absent in the advanced stages of the disease. The gag, withdrawal, patellar, FIG 1: Nomadic sheep flock showing sternal recumbency and inability to lift the head from the ground triceps and anal reflexes were also absent. Pricking the skin with a needle elicited no response, but the ewes appeared to be aware of the needle insult. The ewes were silent, but other vital signs were within normal ranges; the animals were bright and had a good level of consciousness up to the end of the course of the disease, when they died quietly. Electro- cardiographic examination of one of the affected ewes at the end stage revealed no evidence of cardiac dysrrhythmia. The animal went into a state of deep coma before complete car- diac arrest. Its heart rate and rhythm remained normal for 20 minutes after cessation of respiration and its pupils were fully dilated. Fewer than 15 engorged 0 lahorensis female ticks were found on the trunk of each affected animal. Haematology, postmortem examination and bacteriolog- ical cultures revealed no remarkable findings, except for the site of the tick bites on the underside of the skin (Fig 2). Thirty of 400 ewes were affected in an increasing number over a three-day period. Before referral, 15 ewes had died after three days of illness. The affected ewes were treated subcutaneously with 0 2 mg/kg ivermectin (Ivergen; Chemo Iberica and Chemotechnica Sintyal). Twelve to 24 hours later, all of the affected ewes had completely recovered without any residual signs. Ivermectin was therefore administered to the whole flock, and there were no further cases. The three neighbour- ing flocks, which grazed with the affected nomadic sheep flock during the day, were not affected. In this outbreak, botulism was an important differential diagnosis to be ruled out, particularly with regard to the feed- ing of silage. The three other flocks sharing the corn silage, which was prepared satisfactorily, did not have any problems. In addition, sheep affected by botulism do not show the typ- ical flaccid paralysis of other species until the final stages of the disease (Radostits and others 2000), and this ruled out the disease in this outbreak. FIG 2: Tick bite on the underside of the skin of a sheep The Veterinary Record, November 15, 2003 631 group.bmj.com on March 6, 2013 - Published by veterinaryrecord.bmj.com Downloaded from