328 Journal of the Department of Agriculture. — Oct., 1922. 



and llie female begins to lay eggs, so completing tlie life-cycle of tlie 

 worm. 



Sumviarij. — There are thns three non-parasitic stages, i.e. the 

 egg, the first larv i, and the second larva, passed outside on the veld; 

 and Ijiree parasitic stages, i.e., the third larva, fourth larva, and 

 adult ''male and female), passed in the stomach of ihe sheep. The 

 time from entrance of the mature larva into the stomach until the 

 first iaymo of eggs, is about one month, and consideration of this 

 period is, therefore, Ol the utmost importance in any system of dosing". 

 If wire-worm infection is to be eradicated with certainty, dosing must 

 be repeated at least once a month in order to prevent females from 

 developing to the stage at which they can lay eggs and so perjietuate 

 the infection. If they do manage to lay eggs, these hatch out on the 

 veld, develop, promptly re-infect the sheex>. ^^i^f^ restore the vicious 

 cycle. 



Influence of Season. — Since moisture and warmth are iiecessary 

 for development of the eggs and early larval stages, veld infection 

 is greatest during the warm wet periods of the year. The infective 

 larval stage may be reached in three days in warm weather, 1 ut only 

 in three weeks in cold weather; and not be reached at all in frosty 

 weather. A reduced infection of the veld may however prevail all 

 tlie year round, especially in vleis, since the mature larva in its 

 '■ sheathed form," and with its capacity for " migrating " or wander- 

 ing along moist surfaces, will live for a long time. Exposure to direct 

 sunlight and drought will kill it, but under such adverse conditions, 

 it retuins to the soil to hide, only coming out again to crawl up the 

 grass in dull damp weather. If, of course, the worms never find 

 a " host," i.e. sheep or other ruminant, they finally die a natural 

 death. The two practical points to remember are: — 



(1) That an infected pasture may remain infected f(n' at least 



a year, and that all sheep grazing on it during this time 

 are liable to become infected. 



(2) That a living sheep spreads the infection so lone as adult 



wireworms are present in the stomach. 



Eradication of the Worms. — In order to supi)ress the wiieworm 

 plague, it is therefore necessary to kill the wireworms in the stcniach 

 of ihe sheep and to clear the farm of mature larvae. The first task 

 can l)e accomplished by using the Wire Worm Eeinedy supplied by 

 the Division of Veterinary Education and Research. The second is 

 more difficult and takes longer to accomplish. One method would of 

 course be to keep away all animals which act as hosts (sheep, goats, 

 cattle, Inick), for at least a year, and so leave the larvae to die a natural 

 death : but this method is not feasible in ordinary farming. The othei 

 method is to allow the sheep to pick up the larvae in grazing, but t(> 

 kill them off in the stomach before they reach the egg-laying stage. 

 Since the parasitic worm takes from three weeks to a month to reach 

 sexual maturity, the treatment involves regular dosing at least once a 

 month, especially during the rainy season. If this is done, no eggs are 

 laid, no fiesh infection of the veld occurs, and the larvae which are 

 not picked up by the sheep die in time. The farm is then clean and. 

 provided no further infection is brought in from other areas, dosing 

 IS no longer necessary. Although the jxissibility exists that the infec- 

 tioii may be kept alive by ruminants other than the sheep (cattle. 



