Putative filariosis outbreak in white and black rhinoceros at Meru National Park in Kenya
© Mutinda et al.; licensee BioMed Central Ltd. 2012
Received: 25 June 2012
Accepted: 16 September 2012
Published: 19 September 2012
Habitat and food supply loss and disruption, together with man’s pursuit of the animal’s unique horn pose significant threats to the charismatic rhinoceros. Filarial worms have been thought to cause cutaneous lesions in black rhinoceros (Diceros bicornis) in Kenya and South Africa, but never in white rhinoceros (Ceratotherium simum) in the wild, despite the fact that the two species live often in close proximity. Stephanofilaria dinniki has been implicated in the past as the causal agents for such lesions.
In this paper we report a putative filariosis outbreak in both black and white rhinos at Meru National Park in Kenya. Four black and five white rhinos were affected by various degrees of filarioid-like lesions, while apparently all sympatric wild and domestic animals were filarial worm-free. Affected rhinos were captured and successfully treated. Comparison between the epidemiological aspects of white and black rhinoceros filariosis, and the possible relations between this outbreak and annual seasons, the presence of oxpeckers and other host species are discussed.
Our study highlights (i) that filarial infection is not restricted to black rhinos, but it affects both rhinoceros species, and (ii) the importance of the earlier detection and immediate treatment (capture-treat and release) of filarioid infections, which is of pivotal interest for wildlife conservation, and especially the endangered and isolated white and black rhinoceros populations.
The world rhinoceroses’ population has been reduced by more than 90% only in the past 30 years. From the 30 known rhinoceros species once inhabiting our planet, only five threatened species persist today. Only the black (Diceros bicornis) and white rhinoceros (Ceratotherium simum) still roam in Africa. The dreadful plight of this charismatic species is due to habitat and food supply loss and disruption, and mainly because of man’s pursuit of the animal’s unique horn, which poses the single most dangerous threat [1–3].
The causal agent of the frequent occurrence of ulcerative wounds behind the shoulder of black rhinoceros in Kenya and South Africa has been the subject of speculation for many years. The seasonal appearance of the lesions led to the belief that they were associated with secondary sex skin glands, which became active during the breeding season [4, 5]. Stephanofilaria dinniki has been implicated in the past as the causal agent for such lesions [6, 7]. To the best of our knowledge, in all reports only black rhinos have been shown to be affected and not the white rhino species , despite the fact that the two species live often in close proximity . Even so, filarial lesions in white rhinos at Meru National Park (Kenya) have been reported in captivity .
The aims of the present study are: (i) to describe for the first time filariosis simultaneous outbreaks in white and black rhinos from wild populations, (ii) to report the efficacy of filarid infection treatment in this wild animal.
Meru National Park and Rhino Sanctuary, Kenya
This National Park is situated in northern Kenya, covers an area of 870 square kilometres. It has abundant rainfall, 635–762 mm in the west of the park and 305–356 mm in the east. The rainfall results in tall grass and lush swamps, which make it difficult to spot wild animals. It has a wide range of wild animals like elephant, hippopotamus, lion, leopard, cheetah, black rhinoceros and some rare antelopes, with incursions from cattle, camel, goats and sheep. The Meru National Park is a home for 22 black rhinos and 48 white rhinos. During the dry season there are constant incursions of livestock that include goats, camels and sheep in the park area.
The spatial distribution of the infected white and black rhinos within Meru National Park was scattered and isolated points with an average distance of 3 km ranging between 2 and 4 km (No map or GPS references were giving in this paper for security reasons, and to protect these rhinoceroses of being poached).
Macroscopic examination of the filariosis-like lesions and parasite collection
The wounds were quite big; the mean size was 23 ± 8 cm in diameter in the white rhinos, while the black rhinos had much smaller wounds of 15 ± 5 cm. The location of the wounds was varied; white rhinos had massive wounds on the rump, behind the shoulder and the axillary regions, while the black rhinos had wounds on the ribs and behind the shoulder. Red-billed oxpeckers were observed in both rhino species.
Filariae-infected rhinos capture and treatment
Infected rhinos were darted with Dan-inject® dart gun from a helicopter. The dart contained 5 mg Etorphine Hydrochloride (M99®) and 30 mg Xylazine (ILIUM, Troy Laboratories, Australia.) for adult black rhinos and 6 mg Etorphine Hydrochloride and 50 mg Xylazine for adult white rhinos. The animals went down in approximately 6 minutes. After getting down, anaesthetic plan was improved by injecting 5 mg of Nalorphine into an ear vein. In case of the presence of accompanying calves, they were driven away by the help of a vehicle. The animals were then placed on sternal or lateral recumbency to be sampled and treated.
Animals were revived by the injection of 18 mg Diprenorphine (M5050®) and 6 mgs Atipamezole Hydrochloride (ANTISEDAN®) into an ear vein. The white rhinos were also injected with 25 mg Naltrexone Hydrochloride (Naltrexone; Kyron Laboratories) intramuscularly to prevent re-narcotisation. All rhinos got up in approximately three minutes.
Results and Discussion
In the present study we report for the first time a putative filarid outbreak in both black and white rhinos from Meru National Park in Kenya. We failed to collect worms surgically from the subcutis of the immobilized rhinos, and the histopathological examination was negative for the collected samples. Only Stephanofilaria dinniki has been implicated in the past as the causal agent for such filarioid-lesions, and hence we expect this parasite species to be the causative agent of the outbreak of this disease.
The life cycle of S dinniki parasite is unknown. Species of the order to which it belongs require blood-sucking arthropods to complete the cycle . Members of the phylum Arthropoda found associated with rhino are mosquitos, flies and ticks, and hence they can be considered in the transmission of this parasite. Oxpeckers have been seen to peck at the lesions but they are probably not involved in the life cycle but may be attracted by ticks and loose skin. Further studies are needed to understand the life cycle and the vectors of this parasite.
When living conditions deteriorate for hosts, during periods of overcrowding or food shortage, animal become stressed. This stress has often been linked to epidemics, which are attributed to the immuno-compromised status of the stressed hosts [13–15]. In addition, the prevailing environmental conditions could have contributed to lesions and possible filariosis outbreak in both rhino species in Meru National Park. The Rhino Sanctuary at the time of the outbreak was wet, bushy and thick, compounded by dense under growth, while the open areas were most likely swampy patches. Kock & Kock  reported that poor body condition and heavy rainfall were thought to predispose to development of recrudescence of lesions.
One explanation of the high frequency of filarioid outbreaks in wildlife, during the last decades, could be the intrusion of humans and their livestock into wildlife habitat ranges, resulting in great changes in the interface between wildlife and people/livestock, and wildlife habitat losses, and hence the interaction between human/livestock and wildlife is changing from often sporadic and fragile to more permanent and substantial, providing significant opportunities for parasite transmission . The permanent loss of wildlife genetic diversity could have contributed negatively, making wild animals more susceptible to parasite infection [24, 25].
The presence of parasites in any ecosystem generates complex parasite webs within the system, and it is through these webs that zoonotic parasites move from one host to other [26, 27]. Hence, more studies are needed to understand the filarioid-navigating web including potential molecular analyses [28, 29], and the range of underlying causal factors of its unexplicable emergence and re-emergence [24, 30], which poses a substantial threat to the conservation of the global biodiversity .
The Committee of the Department of Veterinary and Capture Services of the Kenya Wildlife Service (KWS) approved the study including animal capturing and treatment protocols. KWS guidelines on Wildlife Veterinary Practice-2006 were followed. All KWS veterinaries were guided by the Veterinary Surgeons Act Cap 366 Laws of Kenya that regulates veterinary practices in Kenya.
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