Hookworms (Ancylostoma caninum, Ancylostoma braziliense, Uncinaria stenocephala) are one of the classical groups internal parasites of puppies, the others being roundworms, tapeworms, and coccidia. Hookworm infection has several features that are of interest to the caretakers of dogs:
Before elaborating on these important aspects of hookworm infection, it is important to understand the life cycle of the hookworm, encompassing how infection happens, how the parasite lives, etc.
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. This means that, like other parasitic worms, they are bathed in intestinal contents but while other worms share the host's food by absorbing it directly through their skin, hookworms feed by drinking their 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. The pet can be infected from contaminated dirt or can be infected by eating another animal that is infected. This could be a prey animal such as a rodent or could be an insect such as a cockroach.
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.
It is worth repeating that the host 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.
(Public Domain Graphic, California Dept. of Food and Agriculture)
Now let us return to the three points we want to emphasize.
HOOKWORMS ARE TRANSMITTED TO NURSING PUPS
Infection of the very young puppy can occur in two ways not addressed in the above description of transmission and will be described now. 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.
(Photo Credit: Public Domain Graphic via Wikimedia Commons)
The hormones of pregnancy unfortunately serve as little wake-up calls to encysted hookworm larvae only this time, the little worms migrate to the unborn puppies and to the mammary gland. This means that most puppies 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.
It is clear why puppies are at a special risk over adult dogs when it comes to hookworms. The Companion Animal Parasite Council has recommended automatically deworming puppies for hookworms beginning at age 2 weeks and continued every 2 weeks through age 8 weeks in areas where hookworms are common. After age 8 weeks, it is recommended that puppies receive a regular dewormer monthly along with their flea and/or heartworm protection product.
CAN WE PREVENT TRANSMISSION FROM THE MOTHER?
The answer is yes but daily deworming is required through the second half of pregnancy and into the nursing period. A regular single deworming will not be effective in protecting the litter. A special protocol using Fenbendazole (Panacur®) has been found to be effective in preventing both roundworm and hookworm infection in unborn puppies.
Ask your vet about this method if you are contemplating breeding a female dog. The Companion Animal Parasite Council has recommended automatically deworming puppies for hookworms beginning at age 2 weeks and continued every 2 weeks through age 8 weeks in areas where hookworms are common. After age 8 weeks, it is recommended that puppies receive a regular dewormer monthly along with their flea and/or heartworm protection product.
The influx of retired racing greyhounds into the pet population has brought with it resistant populations of hookworms. It has been reported in 2020 that most, if not all, racing greyhounds are coming off the track infected with hookworm infections that do not respond to the usual medications. As these dogs mingle with other canine pets, resistant hookworm populations have spread.
When a hookworm infection seems stubborn, a test called a Fecal Egg Count Reduction Test which compares egg counts in fecal samples before and 10-14 days or so after treatment (with the product that is believed not to have worked). A special laboratory may be needed to run this type of testing as it is more commonly done in livestock as resistant parasites have been a long-standing farming issue. The goal of therapy becomes, not clearing the infection, but clearing the clinical signs and maintaining as low an egg count as possible. Testing is done using pyrantel, fenbendazole, and milbemycin oxime in hope of finding an effective product. An egg count reduction of >95% is considered effective. Egg count reduction of <75% is consider ineffective and a combination of multiple dewormers will be needed monthly.
Of all the dewormers to which hookworms are generally considered vulnerable, moxidectin is probably the newest and as long as the dog has not been previously treated with this product, there is a good chance that a combination of dewormers will be effective as long as moxidectin is included. That said, moxidectin-resistant hookworms most certainly exist.
Keep in mind that hookworm larvae encyst throughout an infected dog's body and "leak" into the intestine periodically as they mature. There is no way to clear these encysted dormant hookworms and they cannot be addressed until they make it back to the intestinal tract. There is no way to distinguish a new infection from "leakage" and one infection with resistant hookworms may lead to "leakage" of resistant worms into the intestine theoretically for a dog's entire life.
DECONTAMINATING THE ENVIRONMENT
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. Boric acid can be raked into the soil to kill hookworm eggs but this will kill grass and vegetation as well.
PREVENTION OF FUTURE INFECTIONS
The Companion Animal Parasite Council recommends that dogs be dewormed monthly starting at age 8 weeks. In most areas of the U.S., heartworm products are needed monthly to protect against heartworm disease and most (but not all) heartworm preventives will also prevent hookworm infection. Alternatively, tablets or liquids can be administered separately. The same products listed above as treatments are also preventives.
To view a chart showing which heartworm products work against parasites beyond heartworm click here.
There are two species of hookworms in cats: Ancylostoma tubaeforme and Ancylostoma braziliense, the former being the most aggressive blood sucker . The story is pretty much the same for cats with a few exceptions:
In conclusion, hookworms are significant parasites in both dogs and cats and constitute a human hazard as well. Very young pets are at highest risk for blood so it is important to deworm regularly. If you have further questions or concerns about hookworms, remember your veterinarian is always there to see that you get the answers you need.
Page last updated: 10/24/2021