r 



Figure 22.— Egg of dog 



PARASITES AND PARASITIC DISEASES OF DOGS 25 



most commonly present at the tip of the cecum this is the place 

 where a. reddened area is most often seen. The worm's habit of 

 sewing into the mucosa opens small wounds which probably afford 

 entrance for injurious bacteria. A closely related species of worm 

 in man appears to be responsible for symptoms of distress resembling 

 a low-grade appendicitis. The exact symptoms produced by these 

 worms in dogs are as yet matters which require more careful inves- 

 tigation than they have received. In many cases the worms appear 

 to do little harm and to cause no visible symptoms. 



Treatment. — Whipworms are not very resistant to the drugs which 

 are injurious to parasitic worms in general, but at the same time the 

 removal of these worms is somewhat difficult. Apparently the reason 

 is that it is difficult to get the drugs in contact with the worms. In 

 their passage through the stomach and small 

 intestines drugs are greatly diluted with the con- 

 tents of the digestive tract and are also absorbed 

 to a greater or less extent. Of the amount of 

 drug which reaches the ileocolic valve, at the 

 union of the small and large intestines, only a 

 little and perhaps none will enter the cecum or 'whipworm. ^Enlarged 8 

 get to its tip where the worms are usually g£ m Riley and Fitch > 

 situated. Consequently a single dose of a 

 drug is less likely to reach and kill the worms than it is to 

 miss them. When a number of repeated doses are given, the like- 

 lihood of the drug's reaching the worm is greatly increased. At 

 present the most satisfactory and feasible treatment consists in the 

 daily administration of equal amounts of santonin and calomel in 

 the morning, in doses of one- fourth to 1 grain each, according to 

 the size of the dog, the treatment being kept up for a week, sus- 

 pended for a week, and then repeated for a week. In place of using 

 this routine treatment over a period involving 3 weeks, the treat- 

 ment may be kept up as long as the whipworm eggs appear in the 

 feces on microscopic examination, suspended whenever they disap- 

 pear, and stopped if repeated examinations of the feces show that 

 eggs are no longer present. 



HEART-WORM INFESTATION 



Cause.— The heart worm, Dirqfilaria immitis, of dogs and, occasion- 

 ally, of cats occurs in the right ventricle of the heart and in the pul- 

 monary artery (fig. 23). This worm is long and slender, the male 

 about 5 to 7 inches (12 to 18 centimeters) long, and the female 10 to 

 14 inches (25 to 35 centimeters) long. The eggs hatch in the uterus 

 of the female worm and the larvae are deposited directly into the blood 

 stream. The heart worm is commonly encountered in dogs in the 

 South but apparently this parasite is extending its range to the North. 

 It is found not only in dogs which have been taken South for hunting 

 or other purposes, but also in dogs born and raised in the North that 

 have never been in the South. 



The life cycle of the worm is complex. The larvae which the female 

 worm discharges into the blood are abundant in the blood vessels of 

 the skin, especially at night. Mosquitoes feeding on infested dogs 

 take these larvae into the digestive tract with the blood, and the 

 larvae pass through the walls of the mosquito's stomach and reach the 

 malpighian tubules where they undergo considerable development. 

 Later, the young worms pass to the mouth parts of the mosquito, 



