The parasite we found in the skin nodules had a sac-like body, and the tarsi of legs I and II had pedicillate (stalked) ambulacral discs or spines (Fig. 2a). The female genital opening was a transverse slit lacking epigynium (genital apodemes); genital suckers were absent (Fig. 2b). Tarsi were without apical 'claws' and had some setae modified as stout spines; dorsal striae were broken by strong spine-like serrations. The posterior body setae were short, stout and lanceolate; the anus was terminal (Fig. 2a). These characteristics identified the parasite as a mite, in the genus Sarcoptes, the cause of sarcoptic mange in mammals5,6.

Figure 2: Sarcoptes spp. mites found in nodular skin lesions of a Southern multimammate mouse (M. coucha).
figure 1

(a) Dorsal view shows stalked discs on the tarsi of the legs. (b) Ventral view shows the absence of genital suckers. Low-power bright-field microscopy of unstained specimens suspended in isotonic saline. The microscope condenser has been lowered away from the mechanical stage to enhance the contrast.

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We immediately segregated the infected mice from the main colony. Bedding material was discarded and replenished with freshly autoclaved material. We considered that the source of contamination may have been sarcoptic-infected domestic cattle belonging to the owner of the rice mill from which we obtained the paddy husk used for bedding material. All the animal cages were disinfected with thorough washing in hot water and were then autoclaved. Racks used for holding animal cages were disinfected by washing with phenyl and then dried by hot air. The walls and floor of the room housing the infected mice was cleaned with a hot air blower and then disinfected by thorough washing with bleach and phenyl. As a precaution, we mixed a 5% pesticide dust of Lindane (BHC) with the fresh bedding materials.

Tetracycline (6 mg/L drinking water) was administered to the infected mice to control secondary bacterial infection. We applied benzyl benzoate in a 50:50 dilution with water topically to affected regions and broad-spectrum antibiotics topically to the lesions of the infected mice. A timely diagnosis and treatment with benzyl benzoate, antibiotics and 5% Lindane (BHC) dust caused resolution of lesions in infected mice and prevented further spread of the infection. However, two heavily infected mice did not recover and died during the course of treatment. All other infected mice recovered.

Sarcoptic mange caused by Sarcoptes scabiei (Linn.1758) is distinguished from human scabies by the distribution of papules and vesicles on various parts of the body and the absence of burrows in humans7. Sarcoptic mite infestation of different animals has been reported previously8. In rodents, however, particularly M. coucha, published information on conditions caused by sarcoptic mites is uncommon9. In the present investigation, we describe Sarcoptes mite infection and subsequent dermatological lesions in M. coucha. This infection leads to serious pathology in mice and can result in death if left untreated.

The present report describes the care that must be taken to maintain an animal colony in a geographically remote location. Distance from an urban center and the local climate hinder the acquisition and storage of commercially available animal feed and bedding, such that materials of local origin are a preferred option. These local supplies, however, may be an unexpected source of pathogens. Caretakers must be vigilant in observing animals for possible signs of infection. Fast and efficient diagnosis is necessary to check the spread of any infection in an established animal colony. A high standard of hygiene is the best way to avoid such infestations in laboratory animals.

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