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The hookworm is one of the classical internal parasites of puppies and are common parasites of dogs regardless of age. They are most common in warm humid climates but, exist all over North America. Adult hookworms are voracious bloodsuckers causing blood loss, anemia (low red blood cell count), and enteritis (inflammation of the gut). Hookworm infection has several special features that are of interest to us:
LIFE CYCLE OF THE HOOKWORM
The adult hookworm lives in the small intestine of its host where it hangs on to the intestinal wall using its 6 sharp teeth. Unlike other worms that simply absorb the digested food through their skin as it passes by, the hookworm feeds by drinking its host’s blood. The adult worm lives and mates within the host’s intestine and ultimately, the female worm produces eggs. Hookworm eggs are released into the intestinal contents and passed into the world mixed in with the host’s stool.
The egg hatches in the environment and develops from a first stage larva (the hatchling) to a second stage larva and finally a third stage larva which is ready to infect a new host.
The larva can infect its new host in several ways. One way is to penetrate the host’s skin directly through the feet or belly or whatever part of the skin is touching the ground. Another way for the larva to gain entry to the new host is to be present in soil that is licked and swallowed by the host as it cleans itself.
Once the larvae are inside the host, they make their way to the intestine where some worms simply stay and mature into adulthood. Other individuals are more bold, tunneling out of the intestine, and migrating to the lung tissue. In the lung, the larvae develop into 4th stage larvae and when they are ready they break out of the lung, climb up the trachea (windpipe), get coughed into the throat and swallowed. Once back in the intestine, these well-traveled worms will complete their maturation to adulthood, rejoining any friends they had that never left the intestine on a migration.
Not all the worms that begin this treacherous migration complete it. As they emerge from one tissue to move on to the next, some fall into a state of arrest where they go dormant and encyst. These larvae remain inactive periodically emerging and continuing their migration.
The adult worms live by sucking blood from the intestine. Their eggs are passed by the host into the environment where a new host picks them up. It is worth noting that the host getting infected is not always a pet. Other vertebrates such as rodents and birds can pick up hookworm larvae from the soil. If the pet eats an infected rodent or bird, the pet will become infected just the same as if the infection came directly from the soil.
Clinical signs include: pale mucous membranes, dark tarry stools, constipation, loss of condition, poor appetite, dry cough, and sudden death.
Infection of the very young puppy can occur in a few ways. The hormones of pregnancy unfortunately serve as a wake-up call to encysted hookworm larvae to cause them to migrate to the unborn puppies and to the mammary gland.
Some members of the litter will be born infected. Others will become infected by drinking the contaminated milk of their own mother. If this is not enough to infect the entire litter, others will become infected from the soil of their own nest which will quickly become contaminated with the stool of their infected litter mates. Typically an infected mother dog will have encysted larvae all around her body. Throughout the adult dog’s life, some larvae will awaken, break out of their cysts, and complete their migration to the GI tract.
Hookworm infection can be looked at as a natural check in the canine population as it is frequently lethal to young puppies. A young puppy is growing and growth includes making enough new blood to serve not only its current oxygen needs but what is required for growth as well. Growing requires a tremendous red blood cell production from the puppy’s bone marrow, yet in the hookworm infected puppy this process is being sabotaged by numerous tiny vampires within causing a severe anemia. Ultimately, the puppy may be effectively bled to death.
Infected puppies are commonly pale, weak, and have long-standing iron deficiencies. They may or may not have diarrhea.
Simply killing the worms will not be sufficient to save the life of a severely affected puppy. Like any other blood loss, a transfusion may be needed to keep the puppy alive until it can replace its own lost red blood cells. An iron supplement is frequently needed as well.
Diagnosis is by fecal examination for eggs.
Treatment involves deworming with one of several products. Deworming should be repeated in approximately 30 days. These products are not absorbed into the host’s body from the GI tract and can only kill the worms living within the GI tract. The point of the second deworming is to kill worms in the process of migration at the time of the first deworming, allowing them an additional month to complete their migration. We currently do not have a deworming strategy effective against the encysted larvae in other areas of the host’s body. Interceptor Flavor Tabs, or Heartgard given monthly will prevent hookworm infestations. Puppies and kittens should be dewormed at 2-3 week intervals until weaning. Prevention can be accomplished by annual fecal exams (repeated more often in warm humid climates) or by the use of a monthly wormer in conjunction with heartworm prophylaxis. Breeding females should be dewormed to prevent transmission to their young. Acute cases are treated with fluid therapy and deworming, blood transfusions may be necessary.
HOOKWORMS CAN INFECT HUMAN BEINGS
Hookworm is a zoonotic parasite. Contaminated soil is an important hookworm source when it comes to a human disease called Cutaneous Larva Migrans. Running barefoot through the park or beach may seem pleasant but if the soil has been contaminated with canine fecal matter, the eager infective larvae may be waiting to penetrate your skin. Skin penetration of infective larvae penetrates the bare foot of man and causes mostly a self limiting local skin irritation for three weeks. Cutaneous Larva Migrans (CLM) occurs as red, inflamed lesions in the skin where the larvae of canine hookworms burrow under the skin.
Hookworm infection in the skin is intensely itchy but usually treatable. Humans can also become infected by eating improperly washed vegetables which may harbor contaminated soil. Humans have been found with actual hookworm intestinal infection.
Many people are concerned about how to decontaminate the backyard or property that has housed an infected dog. The good news is that unlike roundworms which are extremely hardy in the environment, hookworm eggs deplete their energy reserves in a few months and die. Further, hookworm eggs do not survive freezing temperatures.
If one uses bleach to clean an area, the protective coating is removed from the hookworm egg and the egg will become dehydrated and will die. Treatment of lawns with a commercial larvacide may also be necessary if repeated hookworm infection occurs.
Most heartworm preventives will also prevent hookworm infection.
Prophylaxis includes regular removal of feces.