Paralysis by Parasite

Image above: Rocky Mountain wood tick (left), American dog tick (right)

Some tick species inoculate neurotoxins that induce a rapid, ascending flaccid paralysis in animals. The 2 species most commonly associated with North American tick paralysis are the American dog tick (Dermacentor variabilis) and Rocky Mountain wood tick (D andersoni). While Rhipicephalus sanguineus is an important vector, its role in paralysis has been purely anecdotal; however, there may be geographic variants that produce paralysis toxins. Fourteen dogs (<8 months of age) from a private animal shelter were heavily infested with R sanguineus in southern Italy. Presentation included ≥1 neurologic sign of paralysis. Neurologic examination revealed reduced or absent spinal reflexes in all limbs with normal pain sensation.

Ticks were manually removed and the dogs treated with a fipronil 10% (S)-methoprene 9% spot-on product. Ten dogs died within 24 hours of presentation; the remaining 4 recovered within 3 days. Hematologic abnormalities included nonregenerative anemia and neutrophilia; several dogs had low-grade thrombocytopenia and hypoalbuminemia. Hepatozoon canis was found on blood or buffy coat smears in 12 dogs; smears from 2 dogs also contained Babesia vogeli. An assay failed to detect antibodies against Ehrlichia canis, Anaplasma phagocytophilum, A platys, Borrelia burgdorferi, and Dirofilaria immitis. Tick paralysis was confirmed by the early and complete recovery of 4 dogs following tick removal and acaricidal therapy.

Commentary

In dogs, tick paralysis is one of the primary differentials for acute diffuse lower motor neuron signs. It is generally accepted that the signs are produced by a neurotoxin released from specific tick species, including D andersoni and D variabilis in North America and Ixodes holocyclus in Australia. Although R sanguineus is the most common tick that infests dogs, it had not been thought to release the neurotoxin that causes tick paralysis; however, this article proposes that R sanguineus may have the ability to cause tick paralysis. This is particularly relevant given the prevalence of this species.—Stephanie Engel, DVM

Source

Otranto D, Dantas-Torres F, Tarallo VD, et al. Apparent tick paralysis by Rhipicephalus sanguineus (Acari: Ixodidae) in dogs. Vet Parasitol. 2012;188(3-4):325-329.