22 



CIRCULAR 338, U. S. DEFT. OF AGRICULTURE 



A third species of hookworm, Ancylostoma braziliense, is sometimes 

 found in dogs in the Southern States. This worm is about the size of 

 Uncinaria stenocephalia; the mouth is armed with 2 large and 2 small 

 teeth. All three of these hookworms may occur in cats, the most 

 common being A. caninum. 



The female worms produce numerous eggs (fig. 20) which pass 

 out in the feces and under favorable conditions may develop in the 

 course of 36 hours to the stage where each egg contains an active 

 embryo. In the course of from 3 to 6 days, as a rule, a first-stage 

 larva hatches from the egg. In about 3 more days this larva molts 

 its skin and forms a second-stage larva. In about 8 more days 

 this larva molts to form a third-stage larva which retains the skin 

 of the previous stage for a time at least. This is the infective larva, 

 capable of infecting dogs when swallowed in contaminated food 

 or water, or when put in contact with the feet or any part of the dog's 

 skin. Whether the larvae enter by the mouth or through the skin, 

 they go into the circulation and behave in much the same way that 

 the ascarid larvae behave, ultimately getting to the lungs, entering the 

 air passages, going up these to the mouth, being swallowed, and 



Figure 20.— Eggs of common dog hookworm. Enlarged. From Railliet, 1893. 



finally reaching the small intestine, where they undergo two more 

 molts and then become mature worms. Eggs from these worms 

 usually appear in the feces in 4 or 5 weeks after infection takes 

 place, but have been said to appear as early as 16 days after infection. 

 In all probability prenatal infection of pups in the uterus of the 

 mother occurs occasionally, and perhaps frequently. 



Symptoms. — Owing to the fact that hookworms are bloodsuckers 

 and that such worms not only remove blood from an animal but also 

 appear to produce poisonous substances which exert an injurious ef- 

 fect on the blood, dogs heavily infested with hookworms usually show 

 anemia (a condition in which the blood is thinner and paler than nor- 

 mal, which is shown by a pale color of the mucous membrane in the 

 lining of the mouth and eyelids) and edema (a condition in which 

 there is an accumulation of serum which seeps from the thinned 

 blood into the tissues and accumulates in pendant portions of 

 the body, as under the jaw). The disease is sometimes referred to as 

 kennel anemia. In early stages of the disease there are digestive 

 disturbances, and in later stages there is often diarrhea, sometimes 

 with blood visible in the feces. Owing to the impoverished condi- 

 tion of the blood and to other disturbances due to the worms, the 



