On December 20, 2000, two of the African wild dogs in one of the breeding packs became ill from an apparently infectious disease. The disease spread rapidly and was first noted in the other breeding packs on January 16, 18, and 22, 2001, respectively. The first deaths occurred on December 21, 2000; deaths peaked from January 30 to February 6, 2001, when 15 of the wild dogs died. The last death was recorded on February 13, 2001. Forty-nine of the 52 animals died during this outbreak.
Neutralizing antibody levels to Canine distemper virus
(CDV), determined by methods similar to those used in a study of large felids (3)
, were measured in serum samples collected from nine African wild dogs on November 8, 2000. One of the three animals that survived the outbreak had a neutralizing antibody titer of 20; the other two were not tested. The sera from the remaining eight animals had a titer of <20, which is considered to be below the level of protection against canine distemper (4)
Tissue samples from nine animals that had died were used for histologic examination (n=6), virus isolation (n=2), and reverse transcriptase-polymerase chain reaction (RT-PCR) with Morbillivirus
-specific primers P1: 5´ATGTTTATGATCACAGCGGT 3´ and P2: 5´ATTGGGTTGCACCACTTGTC 3´, which have been used before for phylogenetic analysis of morbilliviruses (5)
(n=3). The results of analysis were consistent for all animals tested. The main histologic lesion was broncho-interstitial pneumonia with epithelial necrosis and multinucleated syncytial cells. Eosinophilic intracytoplasmic inclusion bodies, characteristic of canine distemper, were found in the epithelium of lung, kidney, intestine, and urinary bladder (). Lung samples scored positive by RT-PCR for a Morbillivirus
P-gene fragment. Phylogenetic analysis of the nucleotide sequences from the resulting PCR fragments demonstrated that the causative virus was most closely related to CDV () and clustered with the sequences of CDV strains from domestic dogs (Canis familiaris
), lions (Panthera leo
), and bat-eared foxes (Otocyon megalotis
) from East Africa in the 1990s (). P-gene fragments of the virus isolates from lung samples were identical to the sequences of the PCR products obtained directly from the tissue samples.
Figure 1 Lung lesions in an African wild dog with canine distemper. Hematoxylin and eosin staining. A. Bronchiole occluded by inflammatory cells and cell debris. B. Detail of A, showing multiple eosinophilic intracytoplasmic viral inclusions (arrows) in bronchiolar (more ...)
Figure 2 Phylogenetic trees based on a 388-bp Morbillivirus P-gene fragment. Maximum likelihood trees were generated by using the SEQBOOT and DNAML program of PHYLIP (Phylogeny Inference Package ) with 1,000 bootstrap replications. When possible, GenBank numbers (more ...)