26 



CIRCULAR 338, U. S. DEFT. OF AGRICULTURE 



escape by breaking through the walls of the labium while the insect is 

 feeding, and enter the blood vessels of the skin through the wounds 

 produced by the bites of the mosquito. The young worms eventually 

 reach the heart where they become sexually mature in 8 or 9 months. 

 Short-haired dogs are more susceptible to heart worms than long- 

 haired dogs, probably because they have less protection against mos- 

 quito bites. 



Symptoms. — The presence of these worms in- the heart may give 

 rise to a variety of symptoms. In hunting dogs the first symptom 

 usually noted is that the animal tires easily; the dog may gasp, breathe 

 heavily and collapse. In cases of long-standing abdominal dropsy, 

 the edematous swellings of the lower part of the chest and legs are 

 common symptoms. A cough may be present, and nervous symp- 

 toms, such as photophobia or fear of light, convulsions, and symptoms 

 resembling those of rabies or hydrophobia have been reported. Death 



may result from asphyxia, embo- 

 lism, and dilation of the heart. 



Diagnosis is made by microscopic 

 examination of the blood for the 

 presence of larvae ; this can be done 

 by any competent veterinarian. 



Treatment. — A drug consisting 

 of sodium-antimony -III-bis-pyro- 

 catechin-disulphonate of sodium 

 has been found of value in the 

 treatment of dogs infested with 

 the heart worm. Intramuscular 

 injections are made daily for 6 

 days each week, treatment being 

 omitted every seventh day. The 

 initial daily dose, administered over 

 the first 6 days, varies from 0.5 to 

 1.0 cubic centimeter, depending on 

 the weight and condition of the 

 animal. For each succeeding 6 -day 

 period, the daily dose is increased 

 by 0.5 to 1.0 cubic centimeter, the 

 maximum daily dose being 3.0 cubic centimeters. In tests in the 

 Bureau of Animal Industry, the total amount of the drug required to 

 effect a disappearance of the microfilariae from the peripheral circula- 

 tion has varied from 21 to 33 cubic centimeters, and the course of 

 treatment has lasted from 20 to 25 days.^ Apparently a maximum 

 concentration of antimony in the system is necessary to effect per- 

 manent sterilization of the blood stream, and, in general, best results 

 are secured when treatment is pushed to the limit of tolerance in order 

 to attain this concentration as rapidly as possible. However, not all 

 dogs are capable of tolerating a continuous course of injections, and 

 in some cases it may be necessary to suspend treatment for a period of 

 several days if unfavorable reactions occur. 



Dogs which are in good condition and which do not show marked 

 symptoms of heart involvement generally tolerate the course of injec- 

 tions without showing marked unfavorable reactions. Other animals 

 show mild to severe systemic reactions which consist in rise in tem- 

 perature and increase in the respiration and pulse rates. In case 



Figure 23.— Heart of dog, showing heart worms, 

 Diroftlaria immitis. 



