ERADICATION OF MITES

Abstract: Pig mange mite infestations are controlled or eradicated by application of a pour-on formulation containing phosmet. A suitable regime is to apply about 20 mg/kg of phosmet to sows shortly before farrowing and to boars at six monthly intervals.

Description: The present invention relates to use of phosmet and an oily carrier for the manufacture of a pour-on formulation for use in treatment for controlling or eradicating an ectoparasite of pigs. Phosmet (0,0 - dimethyl S-phthalimidomethyl phosphorodithioate) is a known insecticide and is used for eradicating Warble Fly, an endoparasitic insect which infests cattle. Pig mange is a particularly refractory ectoparasitic infestation of pigs caused by Sarcoptes scabiei var. suis mites. Hitherto treatment, which is normally by spraying or scrubbing the pigs, has been relatively ineffective and consequently, in the U.K., up to 35% of pigs are infested. It has now surprisingly been found that phosmet can be used to control or eradicate an ectoparasite of pigs, namely pig mange mites. Accordingly, the present invention provides the use of phosmet and an oily carrier for the manufacture of a pour-on formulation for use in the treatment or prophylaxis of pig mange by topical application to the skin or ears of a pig. The phosmet is applied by the treatment topically to the pigs' skin or to their ears. Preferably the phosmet is applied to sows shortly before farrowing, e.g. from 3 to 7 days before farrowing, and to boars at approximately six-monthly intervals. Such a dosing regime restricts the transmission of pig mange mites, between boar and sow at mating and between the sow and her piglets, and avoids the need to treat the piglets. This regime has the advantage that piglets of treated sows tend to gain weight faster than those of untreated sows and piglets of treated sows are, generally, heavier at weaning. Accordingly the treatment also comprises administering phosmet to sows infested with the ectoparasite shortly before farrowing, which treatment promots growth in piglets. Conveniently the phosmet is formulated, as a conventional pour-on formulation, in association with conventional liquid diluents or carriers. One suitable formulation is that currently marketed by Beecham Animal Health under the name αORBISECTα (registered Trade Mark), which comprises a 13.3% w/w solution of phosmet in an oily carrier. Another suitable formulation comprises a 20% w/w solution of phosmet in an oily carrier or a mixture of organic solvents. Suitable diluents and carriers are well known to the skilled person. Preferably the formulation also contains a suitable dye to mark treated pigs and it may also contain agents to mask the odour of the solvents and phosmet, for instance up to about 1% w/w citronella is used in this way. Suitably phosmet is applied at about 15 to 25 mg/kg, preferably about 20 mg/kg of animal body weight. When a 20.0% w/w solution of phosmet is used a suitable dosage rate is about 0.1 ml/kg of animal body weight, optionally with about 1 ml of the dose or in addition to the dose being applied in each ear flap. The invention will now be illustrated by the following Example. Example 1 a) Sows, from a farm with a pig mange infestation were randomly allocated approximately three days prior to farrowing, to one of the following groups: 1) 20% phosmet medicated at a dose rate of 22 mg/kg b.w. A small part of the computed dose (1 ml) was applied inside each ear flap, 2) 2% diazinon and 1% chloroxylenol emulsifiable concentrate (Ficare, Fisons Animal Health, Loughborough) diluted 1 part in 150 of water, used as a body wash at the rate of about 2 litres per sow and, 3) untreated controls. The piglets were weighed twice, first at about 1-2 weeks after farrowing and again at weaning. Average daily liveweight gains (ADLG) were calculated. Results are given in Table 1. b) In a further study on another farm infected sows were randomly allocated to one of the following treatment groups: 1) 20% phosmet medicated at a dose rate of 22 mg/kg body weight with 1 ml being applied inside ear flap and 2) untreated controls. The piglets were weighed at 4 weeks of age. Results are given in Table 2. 20% phosmet has been shown to exert activity against pig mange mites. Further it has been shown that by controlling the level of challenge of mange mites to piglets from the dam, that ADLG was significantly improved (Table 1). It was also found that the average piglet weight at 4 weeks was significantly higher from treated sows than from untreated controls (Table 2). No untoward effects were seen in the pigs treated with 20% phosmet or the piglets. Analysis was based on ADLG of the piglets using least significant difference between groups. ADLG was significantly greater (P 0.01) in the 20% phosmet treated group than in either the diazinon group (2) or the control group (3) A covariance analysis was used, because of variation in litter size, to test the significance of the difference in average weights. This showed that the difference was significant at the 5% level and nearly so at the 1% level, the adjusted mean of the treated group being greater than that of the untreated group.

Claims: Use of phosmet and an oily carrier for the manufacture of a pour-on formulation for use in the treatment or prophylaxis of pig mange by topical application to the skin or ears of a pig. Use according to claim 1, wherein the pour-on formulation is topically applied to sows before farrowing or to boars at 6 monthly intervals. Use according to claim 1, wherein phosmet is applied at from 15 to 25mg/kg. Use according to claim 3, wherein phosmet is applied at about 20mg/kg.

Inventors: YEOMAN, GUY HENRY
Applicants: BEECHAM GROUP PLC
Application year: 1983
Main classification: A01N57
IPC codes: A01N57, A61D7