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An
Overview of Canine Hookworm Infections
Hookworms
that infect canines belong to the Ancylostomatidae family of parasitic
nematodes which get their name from the hook-like mouth parts they use
to attach to the intestinal walls of their hosts. Members of this family
may also infect cats, foxes, and humans. A. braziliense, A.
caninum, and U. stenocephala are the species of hookworm
which can cause infection in dogs and, rarely, in humans. Despite their
small size, hookworms can siphon a large volume of blood from their
hosts and cause serious illness, especially in young dogs. Thankfully
however modern medicine has provided us with a plethora of de-worming
medications, so treatment and prevention of hookworms is relatively
simple and highly effective.
How might my dog become infected?
Hookworm
infections may occur in a variety of different ways. Animals can be
infected by ingestion of larvae from contaminated soil or water, by
eating an infected animal (such as a rodent or other small mammal),
through larvae penetrating their skin, or by larvae infecting fetuses
or the young via the uterus and mammary glands. The exact mechanics
of infection vary depending upon which way a dog contracts the worm
larvae.
Regardless
of the mode of infection, the cycle begins when adult hookworms, living
in the intestine, lay eggs which are then passed in the feces of the
host animal. Within one to three weeks these eggs hatch into larvae.
The larvae are extremely mobile in water and maneuver through moisture
in soil or on vegetation, where they are most likely to come in contact
with a potential host. At this point, paths of infection diverge.
Likely
the most commonly recognized route of infection, larvae often enter
a new host when an animal ingests infested water, vegetation, or even
soil. The majority of larvae simply pass through the stomach and settle
in the digestive system where they will mature. Some however may migrate
to muscles where they will encyst and stay dormant until hormone changes
often associated with pregnancy reanimate them and they become viable
once more, ready to infect a litter of puppies. Transmission by ingestion
may also occur when a carnivore ingests a smaller animal harboring viable
hookworm larvae.
A second
common mode of infection occurs when an animal makes physical contact
with a heavily infested plant, body of water, or area of soil. Hookworm
larvae are capable of burrowing through the skin and entering the bloodstream.
They then migrate to the lungs and through the trachea and are coughed
up and swallowed, after which infection proceeds just as if the larvae
had been swallowed in the first place.
Young
dogs are hit particularly hard by hookworm infections, and most contract
their worms from an infected mother either before birth or via her milk.
How is a hookworm infection diagnosed?
Clinical
symptoms that may suggest your dogs is suffering from an infestation
of hookworms include generalized weakness and pale gums (results of
severe anemia), a dull coat, and significant weight loss. Adult hookworms
are small – only ½ to ¾ of an inch long –
and are rarely visible to the naked eye in stools.
Once suspicion
of infection has been established, laboratory diagnosis is quite simple.
Your veterinarian will examine a stool sample under the microscope in
search of characteristic eggs. If eggs are detected, treatment can begin
immediately.
What are treatment options for dogs infected with hookworms?
A number
of very effective, very safe de-worming agents are available through
your veterinarian. In fact, most puppies are de-wormed as a precaution
as early as 2 or 3 weeks of age.
If your
dog has been diagnosed as having an active infection of hookworms, 2
to 4 doses of the de-wormer will be necessary, as the drugs kill only
adult worms. More than one dose is necessary to eliminate any newly
matured worms that were larvae at the time of the first dose.
In the
case of particularly severe hookworm infestations, your dog may require
blood transfusions in addition to de-wormers in order to combat anemia.
Your veterinarian will be able to decide if this is a necessary step
for your companion animal.
Can canine hookworms infect humans?
Canine
hookworms can infect humans, but because we are not their natural hosts,
they infect us in a different way than they do dogs. Hookworms infect
humans by burrowing through the skin. People may be exposed in a number
of different ways, but most frequently infection occurs when an individual
is lying, sitting, or standing in or on moist soil or sand. Hookworm
larvae penetrate bare skin and their subsequent migration through the
dermis is known as cutaneous larva migrans or, more commonly, “creeping
eruption.” Lesions appear as red lines under the skin and sometimes
break open at the skin’s surface. The condition causes no harm
beyond severe itching, and usually disappears within several weeks as
the larvae die. Very rarely a more severe condition may evolve, causing
lung disease and painful muscles, in which case medical treatment should
be sought.
It should
be noted that human infections with canine hookworms are relatively
rare and can almost always be prevented by avoiding prolonged contact
with moist soil or sand.
What steps can I take to minimize the risk of infection for
both my dog and myself?
Several
steps may be taken to help decrease the likelihood that a hookworm infection
will strike your pet or family member.
All puppies
should be de-wormed at a young age, no later than three weeks of age,
regardless of health status. In addition, females should be treated
both before breeding and again during late pregnancy to reduce risk.
Periodic
de-worming may be indicated for dogs at a particularly high risk for
infection. This possibility should be discussed with your veterinarian.
Proper
hygiene is perhaps the most important factor in preventing hookworm
infections in both humans and animals. The prompt disposal of dog feces
is vitally important, especially in yards, gardens, and public parks.
Dogs should be discouraged from toileting in areas frequented by children,
such as sandboxes or playgrounds. A bleach solution of 3 cups of household
bleach to a gallon of water is a satisfactory cleaning agent for any
surfaces you suspect may have been contaminated. Persons who have contact
with the ground for long periods of time should take the time to place
a barrier between their skin and the earth (i.e. a ground cloth for
someone working in a crawlspace). Since sand is a perfect environment
for hookworm larvae, animals should never be allowed to defecate on
the beach, and people should avoid spending time in damp sand.
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