At a visit to an unfenced desert conservation reserve in Dubai, United Arab Emirates in February 2022, severe skin disease was noted among resident Arabian oryx (Oryx leucoryx), manifesting as dark grayish to black bark-like thickened skin. Between and 45% and 60% of the oryx showed unrest and pruritus. Sarcoptes scabiei was detected at necropsy of six adult animals. Treatment with ivermectin-medicated pellets at 0.3 mg/kg estimated body weight over two periods of 7 d with a 14-d interval between treatments resulted in improved body and skin condition and hair regrowth. Although severe hyperkeratosis was still present shortly after treatment, no live Sarcoptes mites were found in parasitological examination of skin scrapings of two necropsied animals. By 4 mo post treatment the oryx had returned to normal body condition and coat condition.
The Arabian oryx (Oryx leucoryx) is the smallest of three species of the genus Oryx and is native to desert habitats of the Arabian Peninsula; the current status of the species is Vulnerable under criterion D1 (IUCN SSC Antelope Specialist Group 2017). At present, free-living populations of Arabian oryx exist in Saudi Arabia, Oman and Israel, but the United Arab Emirates (UAE) hosts the largest population of more than 4,000 animals.
Literature on parasitic infections on Arabian oryx is scarce. A study in Saudi Arabia detected the coccidean Eimeria saudiensis; the nematodes Camelstrongylus mentulatus, Trichostrongylus probolurus, Nematodirus spathiger, and Trichuris cervicaprae; and the cysticerci of Taenia hydatigena (Mohammed et al. 2012). Of these, only E. saudiensis is host specific; the others have a broad host range and could have been obtained from other desert mammalian hosts. There are only three reports of sarcoptic mange (Sarcoptes scabiei infection) in captive Arabian oryx in zoological gardens (Yeruham et al. 1996; Astorga et al. 2018; Escobar et al. 2022).
We describe an outbreak of Sarcoptes mange in Arabian oryx in the Marmoom desert conservation reserve in Dubai, UAE. Occupying 10% of the total territory of Dubai, the Marmoom desert conservation reserve southeast of Dubai city is the UAE’s largest reserve. The unfenced territory was launched in 2018 and is home to 26 identified species of reptiles, more than 200 bird species, and a number of mammals of which the Arabian oryx is the most striking species in the reserve. The total population of Arabian oryx was estimated by local managers to be 2,000 individuals, concentrating in groups of 10–100 animals around feeding stations. A total of 20 feeding stations (24°45′N, 55°17′E) were built to supply these desert animals with food and water when the reserve was launched (Fig. 1A). These feeding stations were 0.5–3 km apart and fenced, allowing access to fodder and water for oryx and gazelles but exclusion of dromedaries (Camelus dromidarius) that still were present in the initial phase of the project. Trays with pellets, hay racks, and drinking tubs were shaded by roofs made from aluminum sheets, shade nets, and date palm leaves. Amongst the white-coated oryx, individuals with a gray- to black-colored back were first spotted in autumn 2021. Within 4–5 mo, the disease spread to all feeding stations, but the proportion of animals with obvious skin lesions at different feeding stations varied and was estimated to be between 20% and 90%.
In February 2022, observation revealed that affected animals were emaciated and showed unrest and pruritus. Examination of two oryx immobilized by remote injection with etorphine (0.4–0.5 mL per animal; Captivon 98, etorphine 9.8 mg/mL, Wildlife Pharmaceuticals, White River, South Africa) revealed that skin changes, occurring as thick scabs, were not restricted only to the back but were also present on the head, neck, thorax, and legs. The clinical picture suggesting sarcoptic mange (Fig. 1A–C) was confirmed by detecting live Sarcoptes scabiei mites in skin scrapings. During the period of observation, eight Arabian oryx were sent for necropsy. Skin scrapings were taken at the border between apparently healthy skin and crusts. These samples were put in Petri dishes and kept for 20 h in an incubator at 38 C to enable detection of live mites leaving the sample. If no mites left the sample, then after 20 h the skin scraping was dissolved in 10% potassium hydroxide and examined for dead mites under the microscope.
Examination of skin scrapings from six carcasses with generalized mange prior to the start of medication revealed a large number of live S. scabiei mites (Fig. 1D), including their larval and nymphal stages migrating out of the crusts. In histological sections, female mites were seen in burrows in the surface layer of the skin (Fig. 1E).
Because of the large number of affected hosts, it was decided to carry out treatment of all oryx in the area using ivermectin-medicated pellets. This was chosen because other appropriate drugs registered in the UAE (eprinomectin and moxidectin) were in formulations that were not suitable for our purpose. Because of delayed availability of large quantities of an oral formulation of ivermectin (Oramectin, Pharma Swede, Egypt), and organizational problems, initiation of treatment was delayed until July 2022.
Between February and July 2022, the number of Arabian oryx fell dramatically: A census carried out in July 2022 revealed the presence of only 350 individuals. This estimate was possible because in midsummer when temperatures in the desert reach 50–55 C, oryx were concentrated in shaded areas and were easy to count. At that time, scabies-like skin lesions of variable severity were seen in nearly all adult oryx. The feed requirement and dosage of ivermectin was calculated as follows: The body weight (BW) of adult Arabian oryx was considered as 70 kg and the feed requirement of pellets (Roughage pellets, Zabeel Feed Mill) was calculated to be 1.1% of BW (=770 g), considering also the availability of good-quality hay at the stations. An ivermectin dosage of 0.3 mg/kg BW was chosen. The medicated pellets were produced in a portable concrete mixer by mixing 50 kg of pellets with 1.3 L Oramectin (Pharma Swede, Ramadan City, Egypt), 750 mL date syrup, and 600 mL water. To treat 350 animals, a total of 250 kg medicated pellets were required every day during the course of treatment. For 7 d, medicated pellets were distributed to all feeding stations in the late afternoon, depending on the number of oryx per feeding station, and use of the food was monitored. Based on the total development time of Sarcoptes sp. mites (2–3 wk) and the fact that not all oryx might have consumed medicated pellets during the first course, a second treatment course was scheduled after a pause of 14 d.
Two fresh carcasses that were submitted for necropsy 2 wk after the end of the trial were still covered with crusts but no live mites were recovered from skin scrapings.
The general condition of the oryx herds had improved after the two courses of treatment. Less pruritus and unrest was noted and new hair started to grow. By 4 mo after the second treatment course, the oryx had returned to good body and skin condition (Fig. 1F).
The source of the S. scabiei that infected oryx in the Marmoom reserve could not be traced. Previously, sarcoptic mange had been a problem in camels in the UAE, but the experience of the authors over the past 20 yr has showed that camel mange in Dubai has reduced due to wide use of avermectins (Rolf Schulster, pers. comm.). It is also unclear if the camel strain would have infected the oryx. First, although Sarcoptes sp. mites can be transmitted by grooming instruments, blankets and other items, mange is primarily transmitted by direct contact and close contacts between camels and wild ruminants did not occur in this part of the desert. Second, contrary to previous opinions that the genus Sarcoptes consists of several species (Hiepe and Ribbeck 1982), molecular examination has proved the monospecificity of this genus (Zahler et al. 1999). Nevertheless, S. scabiei produces different strains depending on preferred hosts, such as bovines, ovines, caprines, camels, canids, and others. Humans and primates also share their own variants (Deplazes et al. 2021). Because there was no proper management in the reserve, it also has to be considered that S. scabiei–infected oryx may have been introduced into the existing healthy population.
As already mentioned, S. scabies, like other mange mites, are transmitted by contact, and the higher the population density the higher the probability of body contact within the group of hosts during feeding at feed stations. There is no doubt that the oryx population density in this reserve was too high. Although oryx groups around the different feeding stations appeared to be more or less stable, single animals may have merged with other groups and distributed the mite infection especially during the winter time when the cooler weather is favorable for animal movements.
Because S. scabiei live in burrows of the surface layers (stratum granulosum) of the skin, the main clinical signs are pruritus, parakeratosis, hyperkeratosis, hair loss, and skin lesions caused by scratching and rubbing (Bornstein et al. 2001). All these signs were observed in these oryx. The skin is an important organ for thermoregulation and vitamin D production (Cranston 1989, Moriello 2022). Generalized scabies leads to weight loss, abnormal behavior, increased susceptibility to other diseases, and increased mortality (Mörner 1992).
Rowe et al. (2019) reviewed available references on treatment of sarcoptic mange in wildlife and found that ivermectin delivered multiple times via subcutaneous injection at a dose between 200 and 400 μg/kg was found to be the most common and successfully used treatment under captive conditions. Medication of various wildlife species with clinical mange using ivermectin in feed has been reported previously by Yeruham et al. (1996), who mixed an injectable formulation of ivermectin diluted with propylenglycol with feed concentrate. Treatment on three consecutive days was repeated three times at 2-wk intervals.
Our experience with oryx in large numbers kept under free-ranging conditions showed that subcutaneous injection of ivermectin was impractical, because the animals would need to be immobilized by remote injection first and the immobilization and treatment would need to be repeated. Our approach therefore was to treat all animals at the same time orally by mixing ivermectin with feed pellets. To overcome the slight bitterness of the medicine and to increase its binding to the pellets, date syrup was added. To ensure that all animals took up a sufficient dose and in order to break the life cycle of the mites, two treatment sessions took place, for 7 d each, separated by 14 d. The plan was to eliminate adult mites and their larval and nymphal stages with the first treatment cycle, and to kill all the mites emerging from previously laid eggs before they reached maturity in the second course of ivermectin application. Immediately after the two courses of treatment, animals still had mange-induced alterations of the skin, but fresh skin scrapings revealed only dead S. scabiei mites.
We did not observe any signs of toxicity, despite the use of 0.3 mg/kg BW rather than 0.2 mg/kg BW. Contrary to parenteral application, orally administered ivermectin has a broad therapeutic spectrum. Early investigations by Campbell and Benz (1984) demonstrated that ivermectin given orally in a single dose of 4 mg/kg BW (i.e., 20 times the recommended dose) did not cause illness in sheep. Toxicity studies with laboratory rats showed that the no-observed adverse level (NOAL) of orally administered ivermectin for 3 mo was 1.6 mg/kg body weight (eight times the daily recommended dose) and the NOAL for Rhesus monkeys was 1.2 mg/kg BW (six times the daily recommended dose) in a 2-wk study (Lankas and Gordon 1989).
Ivermectin is excreted in the feces, and a review by de Souza and Guimarães (2022) showed that it has a negative effect on soil invertebrates that feed on animal dung. However, none of the analyzed studies were carried out under hot desert conditions, exposing ivermectin, which is ultraviolet light labile and heat sensitive, for several months to 12 h sun radiation daily and ground temperatures reaching 65 C. Additionally, no other drug was available for oral medication of the oryx.
Continuing observation of the situation will show if the chosen method of medicated pellets was successful and if further cycles of treatment will be necessary. In light of this outbreak, we recommended introduction of proper management and veterinary surveillance in the reserve. A wildlife expert should monitor the area periodically to manage the population, treat sick animals, and send moribund oryx or carcasses of freshly dead animals for necropsy, to enable early detection and diagnosis of any future disease outbreak.
The authors are grateful to Mr. Saeed Obaid, to Mr. Jaber Almutaiwei and his team, as well as to the team of Hatta conservation for their assistance during our visits to the reserve.