Combined moxidectin and environmental therapy do not eliminate Chorioptes bovis infestation in heavily feathered horses

Abstract

Chorioptes bovis infestation is a common cause of pastern dermatitis in the horse, with a predilection in draft horses and other horses with thick hair 'feathers' on the distal limbs. The treatment of this superficial mite is challenging; treatment failure and relapse are common. Furthermore, C. bovis infestation may affect the progression of chronic pastern dermatitis (also known as chronic proliferative pastern dermatitis, chronic progressive lymphoedema and dermatitis verrucosa) in draft horses, manifesting with oedema, lichenification and excessive skin folds that can progress to verruciform lesions. An effective cure for C. bovis infestation would therefore be of great clinical value. In a prospective, double-blind, placebo-controlled study, the efficacy of oral moxidectin (0.4 mg/kg body weight) given twice with a 3 week interval in combination with environmental treatment with 4-chloro-3-methylphenol and propoxur was tested in 19 heavily feathered horses with clinical pastern dermatitis and C. bovis infestation. Follow-up examinations over a period of 180 days revealed significantly more skin crusting in the placebo group than in the treatment group. However, no other differences in clinical signs or the numbers of mites detected were found between the two groups. The results of this study suggest that moxidectin in combination with environmental insecticide treatment as used in this study is ineffective in the treatment of C. bovis in feathered horses.

Chronic progressive lymphoedema in draught horses

“…Therefore, even if mites are completely removed, close attention must be paid to identify possible reinfections. Moxidectin , ivermectin and doramectin can fail to eliminate mites completely or to reduce lesions. It is possible that mites become inaccessible within the skin crusts, so oral and systemic therapy for C. equi is not advised.…”

Successful treatment of Sarcoptes scabiei in a 33‐year‐old pony with underlying pituitary pars intermedia dysfunction

“…However, another study reported that moxidectin (0.4 mg/kg bwt) given twice with a 3 week interval is ineffective in treating chorioptic mange as a cause of pastern dermatitis in heavily feathered horses (Rufenacht et al . ). Chorioptic mange of the legs has been successfully treated with local application of a lime sulphur solution 4 times with a 7 day interval (Paterson and Coumbe ) and with either 2 injections of doramectin SC (0.3 mg/kg bwt) 14 days apart or local spraying with fipronil 0.25% solution (Rendle et al .…”

Combined decongestive therapy including equine manual lymph drainage to assist management of chronic progressive lymphoedema in draught horses

“…The moist, densely hyperkeratotic skin surface covered by heavy feathering sets the perfect stage for reinfestation with chorioptic mites and bacterial infections (Risberg et al . 2005; Rüfenacht et al . 2011).…”

“…As shown in humans with lymphoedema (Sisto and Khachemoune 2008; Anon 2009), avoidance of trauma and superficial skin infections is crucial in managing CPL. The moist, densely hyperkeratotic skin surface covered by heavy feathering sets the perfect stage for reinfestation with chorioptic mites and bacterial infections (Risberg et al 2005;Rüfenacht et al 2011). Careful grooming and drying of distal legs, avoiding friction, routine skin scrapings and early treatment of chorioptic mange are crucial, which often requires clipping of the feathers.…”