This disease occurs in various countries, but Australia ranks as one of its classic homes. It is comparatively rare in our larger cities now due mainly to centralisation of slaughtering, meat inspection at abattoirs, and exclusion of dogs from same. In rural communities, however, the position is far from satisfactory and calls for a definite campaign aimed at the control and eventual eradication of the disease. The purpose of this article is to give some understanding of the problem and to indicate how all may take part in such a campaign. As over 30% of sheep and cattle and 23% of dogs on the tablelands of N.S.W. are infected, it is obvious that we of New England are especially concerned.
In the first place it may be mentioned that man can never become infected from sheep or cattle directly, but only by way of the dog, though this may happen in any one of a variety of ways. To be strictly correct one should include with the dog certain other animals, such as the fox and the dingo, but these are of minor importance. If the entire canine population were freed—and kept free—of the tapeworm concerned, hydatids would soon cease to be a problem. It might be mentioned here that, contrary to common belief, rabbits are of negligible importance in the dissemination of this disease, being rarely, if ever, infected with the true hydatid parasite—it has never been reported in Australia. (The large cysts sometimes found in rabbit carcases are the intermediate stage of a large tapeworm of the dog and have no relation to human health). Also, it is doubtful whether the cat is ever naturally infected with the mature worms.
The tapeworm concerned is a very small one which infests dogs. The droppings of an infected dog contain material which includes the eggs of this parasite which may contaminate drinking water, grass, vegetables, etc. As well as direct contact occurring, the eggs may be blown about with dust, carried by flies, etc. When any of these eggs are swallowed by such animals as sheep, cattle or pigs (or kangaroos, elephants, etc.) or by man, they can develop into the intermediate or cystic stage of the parasite, which is commonly seen in the liver, lungs, etc., of such animals. It is by eating uncooked organs containing these cysts that the dog becomes infected, and thus the life cycle of the worm completed.
Many precautionary and control measures should now be obvious, but it may be helpful to outline some of the more important of these. First, we must aim at the elimination and prevention of infection of the dog. The main point here is to see that dogs are never allowed to eat raw offal (especially livers of sheep) unless it is certain that the latter is not infective. If you kill sheep for rations, then keep a kerosene tin of boiling water handy, and as soon as liver, heart and lungs are removed, drop them in and leave them there for 10 minutes before feeding them to dogs.
Station dogs and slaughter-house dogs are definitely the most important factors in spreading this disease. There should be no slaughter-house dogs and station dogs should be treated every eight weeks with arecoline hydro-bromide to remove the adult tapeworm (see below). The treatment of every dog in the district during health week would be a splendid move, and if treatment were repeated once or twice yearly the district would benefit greatly.
The following points in the prevention of infection of man deserve special mention. Always wash after handling country dogs, particularly before rolling cigarettes or handling pipes, food, etc. Do not allow young children to crawl in the vicinity of the kennels, nor to play with dogs except under supervision. Boil all drinking water from doubtful sources (actually, there is less danger in drinking from the surface of streams than in using water from the tap of an uncovered iron tank, as tapeworm eggs do not float; but in the former case there is also the possibility of becoming infected with liver fluke). It is advisable to wash before eating, etc., after handling sheep or wool, as these might be contaminated—by infective dust, for example. Theoretically at least, lambs should not be castrated with the teeth, for the same reason.
Dog yards should be situated well away from the house, and fly traps placed near these and killing pens help to reduce the danger of human food being "infected" by flies. To be really thorough, the droppings should be collected daily from dog yards and burnt. As far as possible dogs should be excluded from vegetable gardens, and all vegetables which are eaten raw—in salads, etc., should first be washed thoroughly, preferably in running water.
Treatment of Dogs:
Treatment of this and other tapeworm infections in dogs formerly consisted in the administration of freshly ground arec-nut in dose rate of two grains per pound body weight, followed by a moderate dose of castor oil (1 to 4 dessertspoons), after starving overnight. It is now considered, however, that arec-nut is a dangerous drug, frequently causing inflammation of the bowels, and it should certainly never be used for puppies nor for debilitated animals. (It is unsafe for cats, as it might cause suffocation. Use kamala to treat cats for tapeworm infections).
Extract of male-fern may also by employed, in a dose of ¾ to 1 drachm, but might not be completely effective—in which case it should not be repeated within a few days; also it is dangerous to follow male-fern with castor oil or any other oleaginous purgative in the case of dogs; if it is wished to use this drug give a saline aperient (e.g., a dessertspoon of epsom salts) 12 hours before and again six hours after it.
Treatment with arecoline hydrobromide is now considered the best. This drug is administered as tablets, or in the form of aqueous solution containing 1/16th of a grain per drachm (½ grain tablet in 1 ounce water). No other purgative is required, arecoline itself having this action. The dose rates are:
For small puppies and "toy" dogs, 1 drachm (=1/16th grain);
For small terriers, 2 to 4 drachms (=⅛ to ¼ grain);
For large terriers, snail kelpies, etc., 8 drachms (=½ grain);
For large sheep dogs, greyhounds, etc., 1 to 2 oz. (=½ to 1 grain).
Note.—Some authorities give ⅛ to ¼ grain as the range of dog doses.
When treated the dogs should be tied up until all purgation has ceased, and any droppings should then be collected and burnt, since they are likely to contain large numbers of tapeworm segments and eggs capable of infecting man, sheep, cattle, pigs, etc., as explained above.
It is as well to remember that a dog might be fat and sleek, and appear in or perfect health, and yet be heavily infected—harbouring perhaps five or six thousand tapeworms— and thus a menace to humans, especially children. Young dogs are more likely to show symptoms, such as rubbing the tail along the ground, sudden bursts of excitement—the dog jumping up and running about for no apparent reason—or rubbing the belly along the ground, or rolling. Other possible indications include dull and depressed periods, and "fits."
Lest there be any confusion regarding the identity of this parasite, it might be explained that it was originally known as Taenis echinococcus, but is now called Echinoccus granulosus. The form seen in sheep, cattle, pigs etc., is the intermediate larval, crystic, or bladder-worm stage. The importance of the dog, as primary host, will be evident from the foregoing. Of the intermediate hosts the sheep is pre-eminent from the public health stand-point for various reasons. Including the fact that 90% of the cysts occurring in this animal are capable of infecting dogs, whereas a large proportion of those in cattle (90%) and pigs (20%) are sterile; also the sheep population of this country is so large, and dogs have access to raw sheep offal so commonly.
Though it is thought that heavy infections may cause death of sheep in some countries (e.g., Bulgaria), the health of domestic animals seems to be very little affected in Australia. In man, however, the disease is very serious, though it seems that symptoms may only become marked some years after infection. These result from pressure on the surrounding tissues, causing pain and interference with the normal functioning of the organ concerned. Thus a cyst in a lung may cause pain and interference with breathing; in the liver there might be extensive fibrosis; in a bone necrosis and rarefaction, predisposing to fractures. Rupture of a cyst may result in collapse from a type of shock, and even death from absorption of toxic products in the hydatid fluid; failing this it may lead to the formation of innumerable "secondary" cysts in the body.
Aids to diagnosis in the human subject, which is not simple, include a skin test (the Casoni reaction) not unlike that sometimes used to detect tuberculosis in cattle, and an even less reliable test of the blood serum similar to that used for "Pleuro," in the same species.
Medical science, including surgery, can do much for us in dealing with this disease, but we can do more ourselves, in the way of prevention, medical and veterinary science having shown the way. Let us commence now, in this our Health Week.
Note: In the preparation of this article, originally written at the request of the Health Inspector for use in connection with Glen Innes' Health Week, 1942, the very useful book, "The Internal Parasites and Parasitic Diseases of Sheep," By I. Clunles Ross and H. McL. Gordon. 1936 (Angus and Robertson Ltd) Sydney was freely drawn upon.