DIAGNOSING PARELAPHOSTRONGYLOSIS IN MOOSE (ALCES ALCES)

Abstract

Thirty-six moose (Alces alces) reported as acting abnormally were examined in northwestern Ontario and adjacent northeastern Minnesota in 1986 – 2000. Thirty-four typically had little fear of humans, remained in an area for some time, and showed clinical signs of neuromotor incoordination including walking in circles, showing weakness and difficulty in rising, head tilted to one side, or standing with legs positioned wide apart. A definitive diagnosis of parelaphostrongylosis was confirmed in 15 (44%) of these by finding small numbers (2.5 ± 0.6; 1 – 9) of adult meningeal worms, Parelaphostrongylus tenuis, within the cranium; the meninges of 12, (excluding 3 unsuitable for examination), were cloudy in appearance. An additional 5 clinically abnormal animals had no visible P. tenuis but presented with cloudy inflammation of the meninges. No evidence of infection other than typical neurological signs was found in 14 more, but examination was impossible or incomplete for 9 of these. One, however, had P. tenuis-like, dorsal-spined larvae in its feces and another tested positive for P. tenuis using the newly developed serological test (ELISA). Female animals predominated in the sample (21/34) and 10 were judged underweight. The remaining 2 moose in the sample, although aggressive towards humans, had no worms visible in the cranium and neither showed neuromotor signs or cloudy meninges; 1 tested using the ELISA was negative for P. tenuis. Moose with adult P. tenuis in the cranium were younger (1.8 ± 0.5 yr) than those abnormal animals without worms (5.2 ± 1.2 yr) (U = 20, P = 0.006). Five of 15 moose with adult worms in the cranium were passing small numbers of dorsal-spined larvae in their feces (0.1 – 2.8 larvae/gm). Sixy-five percent of animals exhibiting typical neuromotor clinical signs of moose sickness showed post-mortem evidence of parelaphostrongylosis. The diagnostic reliability of clinical signs would have been further increased by wider use of the P. tenuis ELISA. This is a convenient, commercially available test and potentially a valuable tool for investigating the level of P. tenuis exposure experienced by moose populations sharing range with infected white-tailed deer.