ARCHIVE FILE
See the original document
INSTITUTE OF INSPECTORS OF STOCK OF N.S.W. YEAR BOOK.
DIROFILARIA (Heart Worm) IN DOGS
F. T. Yeoman, Inspector of Stock. Moree.
This parasitic infestation in dogs came under the writer's notice in the North-West for the first time about three years ago, and since that time six (6) outbreaks have been seen. It appears that the first outbreak in the district occurred about 20 years ago, and that since that time the trouble has appeared sporadically on the property from which it was first reported. Just why it has not increased generally over the district is difficult to say, but it is most fortunate that this has not been so.
It has been noted that dogs of all types, and of all ages from four months up, may become affected; while it is a fact that recoveries have not been seen, mortality being 100%. It has been stated that foxes found dead have been affected with this parasite, but this has not been confirmed personally.
Symptoms.—There does not appear to be any characteristic symp-tom which can be specified as diagnostic of the disease. The affected animal first shows a general lassitude, then a disinclination to move at all; though it will continue to keep on its feet. Looking round at the side, with a distinct moan and sometimes even a snappy bark, will be noted in most cases. Food is declined but water is taken freely, even when the dog is prostrated just prior to death.
Post-Mortem.—On opening the heart of a dog that has died of heart worms one is astonished at the manner in which the auricles and ventricles, and even the aorta, are gorged with the parasites, some extending into each cavity. The number of worms in a heart at times would be sufficient to fill two ordinary egg-cups. The parasite itself is clean white in colour, up to 10 inches in length, has the thickness of coarse thread, tapers at both ends and is particularly tough in texture. Apart from the heart lesion, autopsy does not reveal any abnormalities other than a slightly darkened colour of the liver, though it is thought that in some cases the heart is somewhat distended.
Treatment.—Following on advice from Glenfield Research Station to the effect that dog fleas were the intermediate hosts of Dirofilaria, owners of dogs on properties where mortalities occurred were advised to free the dogs and the areas in which they were confined of fleas by frequent disinfection and the removal of kennels from place to place. It is believed that these measures have reduced infestation considerably; in fact, one property on which there were frequent outbreaks prior to this treatment has not had any trouble during the past twelve months.
Glenfield also advised that the drug Fouadin has been used for curative treatment; given intra-muscularly or intravenously. This drug kills the worms in the dog's heart, but apparently can be of little assistance in the removal of the dead worms from the body. It has been reported that many complications take place after the treatment; such as prostration and stiffness of gait, loss of appetite and symptoms of pneumonia. This latter condition requires the greatest care, nursing and veterinary attention; which generally is not available to the ordinary dog-owner in the country.
It will be realised that should this disease become prevalent among dogs, particularly sheep-dogs, the economic loss to sheep owners throughout the State would be enormous. Station work would become disorganised, and from this angle the problem must be viewed as a most important one; affecting the production of livestock and even seriously threatening the stock industry.
(Life History.—Active larvae, corresponding to first stage larvae of other nematodes, are discharged directly into the blood stream, where they are most abundant in the peripheral circulation during the hours of darkness. Larvae continue to circulate until they are removed from the blood stream by some blood-sucking insect.
From Hutyra, Marek and Maminger (1) and Monning (2) it is obvious that mosquitoes of the genera Anopheles, Aedes, Myzorhynchus and Culex, as well as certain biting files, have been proven intermediate hosts for many years. Development in the mosquito occurs in the Malpighian tubes and takes 15-35 days. The infective larvae then pass to the labium of the insect and are transferred to the final host by the bite of the mosquito. Adults can live for several years in the final host.
It has been suggested that certain fleas also can act as intermediate hosts. It is not known whether experimental transmission of Dirofilaria through the bites of fleas has been demonstrated, but Brown and Sheldon (3) found the infective stage of the heart worm larvae in naturally infected fleas. From the effectiveness of preventive measures in the Moree District, and in a particular area in which mosquitoes are plentlful, it would appear that dog fleas are of much greater significance than are mosquitoes as intermediate hosts on this country.
Treatment.—Wright and Underwood (4) recommend injections of Fouadin in the following doses for dogs 22-33 lbs. in weight:—Intramuscularly — first six days 1 ml.; then 1.5 mls. daily; no treatment every seventh day. Intravenously — 1 ml. on 1st, 3rd and 5th days; 1.5 mls. on 7th and 8th days; 2.0 mls. on 9th, 10th and 12th days. It is stated that the latter treatment is more rapid and is suitable for dogs in good condition; but that treatment is not well tolerated by dogs with infestations of long standing, which have produced organic heart diseases, hyperplasia of the walls of vessels in the liver and kidneys, with cirrhosis and chronic interstitial nephritis. To such dogs smaller doses should be given, with careful observation and suspension of treatment on the appearance of adverse reactions. The microfilariae are said to disappear rapidly, and the adults to die off gradually, after treatment. Fouadin is claimed to have a cumulative action, and to be excreted mainly in the urine.—Editorial Committee).
References—
(1) Special Pathology and Therapeutics of the Diseases of Domestic Animals—Vol. 3, 1938. (Bailliere, Tindall & Cox, London).
(2) Veterinary Helminthology and Entomology-1938. (Bailliere, Tindall Sr Cox, London).
(3) North American Veterinarian. 21; 230-231.
(4) Veterinary Medicine, 29 (6): 234. 1934.