output of (Tinss is tliiis olitjiiiu'd. fnc fmni iliscasc oi'|;!>>>>"<"'< 

 mid iiidopoiidont of rliiiiatr. 



(k^i Cookinii — Larvai" cani'.-d liv food aiiiinalH arc dcsl roved 

 liy lii'atinK and so all meat and tisli foods fed to pitjs or car- 

 iiivori's should bo cooked unless free from siispicion ; this is 

 liiKlilv important in the control of the trichina. 



U) Flourboarils — The use of floorlKUirds, wire or concrete 

 Hoors for i>iKs, carnivores and poultry, provided they are kept 

 clean, niit only iiermits of ellicient I'nj; destruction lu elitnina 

 tion, liut prevents infection, or .it least reduces it very con 

 sideralily. 



(ni^ Qiuiraiitiiii — New stock should not be introduced to a 

 worm controlled farm, until it has tieen carefully cxainincd 

 for parasites. A single boar, for example, may introduce 

 ascarids to a worm free pigBeiy. Kiioiin c.irriers of any 

 kind of parasites already present should be treated, iso- 

 lated or at least excluded from common crazing. Wild aiii 

 mals which harbour parasites communicable to domestic nni 

 mals should be denied access or be destroyed. 



Vectors 



Many roundworms of domesticated animals, require essen- 

 tial intermediate hosts. These may be arthropods, earth- 

 worms, snails, or vertebrates such as fish, amidiibia, and 

 even other mammals. A knowledf;'' of the life history of 

 both carrier and parasite is essential before control can be 

 nndertaken. This may involve not only destruction of the 

 vector but avoidance of infection of the vector, in many 

 oases a procedure of almost equal importance. 



Destruction of infective larvae in vertebrates may be un- 

 dertaken by meat inspection and physical or chemical de- 

 struction of condemned material. Cooking of all garbage 

 fed to pigs is an invaluable means of controlling Trichina 

 in pigs and so in man. In the case of pork for human con- 

 sumption, thorough cooking until the flesh turns white, is a 

 perfect safeguard; pork is often eaten undercooked. Where it 

 is eaten raw. it should be subjected to chemical treatment, 

 chilling or heating (as laid down in the regulations of the 

 I'nited States Bureau of Aiiiinal Industry). 



Earthworms carry a considerable number of parasites to do- 

 mestic animals and their control is extremely difficult. Chemi- 

 cals and sand have been used but more successful results are 

 obtained by avoidance of. infection. 



Insect destruction is almost as difficult. Most of the im- 

 portant carriers are dung feeders and are not easily attacked. 

 Many of the usual contact or stomach ]ioisoiis are available but 

 their use has been extremely limited. A more rational means 

 of control is an attack on the breeding places and this is 

 feasible for house flies, mosquitoes and ectoparasites. 



Avoidance of infection of the vectors is almost as im- 

 portant as their destruction. This can be effected not only 

 by proper manure disposal and treatment, but by means de- 

 signed to keep animals and vectors apart. Thus, for ex- 

 ample, the lungworms of swine are carried by manure-fre- 

 quenting earthworms; if swine faeces are disposed of in 

 situation where the swiue themselves cannot reach the para- 

 sites can be controlled. Swine confined entirely to proper 

 concrete pens, should never have lungworms. 



In cases where the larvae are actually removed from the 

 bodv by biting flies, protection from these will not only 

 prevent vectors becoming infected hut will prevent the hosts 

 being infected in turn. In addition, of course, measures for 

 the control of these insects (mo.squitoes. midges, black flies 

 and stable flies) should be undertaken. 



As the spirurid nematodes are carried l;irgely by dung-fre- 

 quenting insects, manure treatment and disposal will help to 

 reduce infections. 



Destruction Within the Host 



Antiparasitic drugs are used for two purposes — to treat 

 clinical cases or to provide a clean herd. The first requires the 

 removal of only sufficient parasites to relieve the symptoms; 

 the second postulates a much more efficient drug, one which 

 would destroy all parasites being the ideal. There are few such 

 drugs availalde as yet and such as are, may be used with suc- 

 cess against a comparatively small number of species; fortu- 

 nately, however these include some of the important forms. 

 Where these drugs are available, for either internal or external 

 parasites, their use as a means of control is highly important. 

 All members of the herd should be treated regularly until all 

 parasites have disappeared and no residual infection left to act 

 as a starting point for re-infection. 



This mass treatment, where it has been employed correctly 

 and under strict supervision, has given excellent results. It is 



ncccssaiy to emphasii'.c the necessity for strict supervision. .Ml 

 drugs used to destroy parasites ari' animal poi.sons, at least to 

 sonic exii'iit. and their indisi rimiii.'ili' use by l;iyinen is apt not 

 only to nullity their results but to be actii.-illy dangerous to 

 the animals. Their use ;iccordingly requires the aid of the 

 practicing vi'terinarian. No other jierson knows the h.'ibits and 

 location of the parasite, the physiology of the host, the correct 

 drug to use, the technique of its administration and its contra- 

 indications. If this jirinciple is accepted, it follows that co- 

 (qierative district schemes, involving panels of jiractitioners, 

 .•ire essential. It is useless, as a control measure, to er;idicate 

 any |iarticular parasite on one farm if the next remains lic;ivily 

 infested. The first sti'ps to be taken must be those of an cdii 

 cational nature to be followed by some cii.'ibling order frinii a 

 higher .•luthoiity ; this order, however, should come only as the 

 result of a demand from the district itself. Thereafter, by a 

 suitably designed veterinary jianel treating animals in groujis 

 in sub districts, the entire population in the district can lie 

 treated ipiickly, cheaply and efficiently. 



Reservoir Hosts 



NVild aitiin.'ils belonging to the s;iiiu' major groiijis as domcsti 

 cated ones, often harbour jiarasites transnii.ssible to them and 

 there are innumerable cases on record of such animals or even 

 animals more distantly related, acting as reservoirs of infec- 

 tion as well as transmitters of new species to domestic :.ni- 

 mals. It is of ini])(irtaiice to know what parasites occur in the 

 wild fauna of a cdinitry or district and to take such stejis 

 as may be possilile to keep those parasites ivithin control. 



At present only one or both of two jilaiis of action are avail- 

 able; cither to destroy all the wild carriers or to prevent their 

 intermingling with domestic ones by suitable segregation. 



Indigenous wild mammals and birds not only possess jiara- 

 sites transniissilile to man and to domesticated stock but may 

 become infected from the introduced stock and act as uncon- 

 trolled reservoirs of the new iiarasites. An adequate knowledge 

 of the parasitic fauna of the indigenous wild animals is an es- 

 sential steji in controlling parasites of domestic stock. It is 

 surprising how little has been done. The Institute of Parasi- 

 tology in Canada is conducting such a parasitological survey to 

 ascertain the distribution and intensity of infections in all 

 forms of animal life in the Dominion. A large amount of 

 voluntary assistance in collecting has been readily given by 

 all classes of persons — official, commercial and private — and 

 although many years must pass before the survey is even aji- 

 proximately complete, it has already yielded invaluable re- 

 sults. This survey has also been extended to the West Indies 

 and it is to be liojied that other countries will take similar 

 steps and enable a world map to be prepared showing the dis 

 tribution and importance of all parasites in all kinds of animal 

 life. 



Avoidance of Parasitic Disease 



Effective control of any species of parasites will eliminate 

 the disease caused liy it, but even when this cannot be done, 

 steps should be taken to reduce or avoid the disease. With a 

 very few obvious exceptions, disease depends on numbers of 

 parasites present but we are unable to state the exact point at 

 which clinical disease begins, even if we admit the theoretical 

 concept that even a single jiarasite causes some disease. There 

 is too little real knowledge aliout the action of parasites and 

 too many factors involved, including nourishment, resistance 

 and presence of other parasites. 



In general, however, it may be stated that any attemiit to 

 reduce the number of parasites ingested, to increase the re- 

 sistance of the host or to raise the standard of fitness of an 

 animal offsets the effects of the parasite to some extent and 

 helps to reduce parasitic disease even if it does not eliminate 

 parasitism. 



(a) Prireutivc Licks — The theory underlying the use of pre- 

 ventive licks is that a small daily dose of some drug taken in a 

 mineral lick, will either kill the larvae taken in the food or 

 else render their environment so abnormal that they will not 

 develop; it is not suggested in this way to administer drugs 

 against adult parasites. There is no conclusive proof yet that 

 preventive licks are .satisfactory. Good results have been 

 claimed with tobacco and bluestone, but the subject must still 

 be considered as in the exiicrimental stage. 



There is no doubt that the efficiency of some of the older 

 worm medicines was due to their "tonic" action on the liody 

 and that this was particularly the ca.se with such elements as 

 iron, copper, cobalt, arsenic, phosphorus and calcium. These 

 appear to be used by the body to repair or counteract damage 

 done by the parasites, as well as in some cases to destroy the 

 parasites themselves. A supply of such materials in mineral 

 licks is often of great importance in jireventing the develop- 



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