Toxocara cati (Roundworm) Toxocara cati is the most common of the intestinal nematodes of cats, and in the opinion of many, the most important. These
are the largest of the feline intestinal nematodes (3-10 cm) and are similar in appearance to the canine roundworm, T. canis.
The few prevalence studies that have been conducted in cats in the United States indicate that T. cati is the generally the
most common. For example, T. cati was present in 43 percent of 60 cats surveyed in Kentucky and Illinois, and in 92 percent
of the 13 control cats acquired for the anthelmintic study conducted in Arkansas. Researchers at Cornell University have conducted
fecal examinations on both shelter cats and cats that were privately owned. The combined prevalence of T. cati in the two
cat populations was 33 percent (n=263 cats). The prevalence of T. cati in shelter cats was 37 percent. Surprisingly, the prevalence
in privately owned cats was 27 percent. Although some of the surveys indicated that juvenile cats are more likely than adult
cats to maintain patent infections, other sources indicate that cats retain their susceptibility to T. cati infections throughout
their lives.
Toxocara cati can be contracted in several ways: ingestion of embryonated eggs, consumption of transport hosts such as mice,
birds, cockroaches, and earthworms, and by transmammary transmission from the queen to her kittens. The transmammary route
is apparently quite common. Toxocara cati undergoes a liver-lung migration, typical of other ascaridoid nematodes, before
establishing in the small intestine. The developmental period for T. cati in the cat varies depending on the route of infection
and host factors such as age. Adult worms are prolific egg producers and are estimated to produce as many as 24,000 egg per
day. Eggs require three to four weeks in the environment to become infective, and can remain viable in the soil for months
or years.
Kittens infected with T. cati can display signs of infection similar to those observed in puppies infected with T. canis,
i.e. enlarged abdomen and failure to thrive. Vomiting and diarrhea also have been observed. Infections also can result in
pulmonary lesions, as well as signs such as coughing and sneezing as a result of migration of the parasite through the lungs
or upper respiratory tract. Migration through the liver apparently occurs without adverse effects.
Photo 3: Egg of Toxocara cati from fecal flotation.
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It is important to remember that Toxocara cati, like other roundworms, also may cause disease in humans, particularly children
that accidently ingest embryonated eggs from contaminated environments. The resulting disease syndromes are known as the larva
migrans. Visceral larva migrans (VLM) is caused by migration of larvae through the internal organs and may result in pneumonitis
and hepatomegaly, with accompanying eosinophilia. VLM generally occurs in children less that 3 years of age. In older children
(generally 3-13 years), a second syndrome, known as ocular larva migrans (OLM) can result in severe ocular damage and subsequent
retinal detachment, loss of vision, and even blindness. Interestingly, recent studies in a laboratory animal model of human
ocular disease indicate that T. cati has the capability to cause ocular disease in laboratory animals that is approximately
equivalent to T. canis.
Diagnosis of T. cati infections are confirmed by recovering the typical nonembryonated eggs in feces (see Photo 3). Eggs are
smaller than those of T. canis, but are structurallysimilar to them. Occasionally feces and vomitus will contain expelled
worms.
Table 4: Selected feline internal parasiticides
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Because of the longevity of eggs in the environment and because of the difficulty of preventing exposure of cats to eggs or
larvae of T. cati., the best approach to control of feline toxocarosis is to treat cats periodically to remove adult worms.
Several anthelmintics are available for removal of T. cati (see Table 4). Those compounds with activities against other parasites
such as heartworms and/or fleas are particularly appealing because of the necessity to control these parasites.
Ancylostoma tubaeforme/A.braziliense (Hookworms) These are small (5-12 mm) worms, that live in the small intestine of cats (See photo 4). Ancylostoma tubaeforme is similar
in life cycle and pathogenicity to the common hookworm of dogs, Ancylostoma caninum. Ancylostoma tubaeforme appears widely
distributed geographically, while A. braziliense is limited to tropical and subtropical regions of the world. Many veterinarians
believe that hookworms are neither common nor of any significance as causes of disease in cats. Unfortunately, neither of
these presumptions is always true. In the study mentioned above, Ancylostoma. tubaeforme was recovered from 75 percent of
the 60 cats of cats from Illinois and Kentucky. In the other study cited above, Ancylostoma tubaeforme was present in 77 percent
of cats examined in Arkansas. In the Arkansas study, A. tubaeformae was exceeded in prevalence only by Toxocara cati. In my
laboratory, we are in the process of determining the prevalence of internal parasites in cats from east central Alabama. We
have examined 52 cats to date. Thus far, we have recovered A. tubaeforme from 27 percent of the cats and T. cati (see previous)
from 23 percent. Interestingly, seven cats harbored both parasites. Also, these parasites were found in cats ranging in age
from 1 to 6 years and not just in kittens as one might suspect. We have also recovered both of these parasites from similar
numbers of male and female cats.
Photo 4: Intestine from a cat experimentally infected with Ancylostoma tubaeforme. Note the presence of blood on the mucosal
surface and attached hookworms. Top: Enlargement of an attached hookworm.
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Cats acquire hookworms by several exposure routes. They can be infected by ingestion of infective larvae, by skin penetration,
and by consumption of transport hosts containing tissue larvae. Apparently neither transmammary nor transplacental transmission
of hookworms occurs in cats. Larvae of feline hookworms undergo migration through the lungs prior to maturation of adult worms
in the small intestine. The entire life cycle requires about three to four weeks, depending upon the method of infection.
Studies have shown that A. tubaeforme can cause hookworm disease in cats. Experimental infections can cause weight loss and
anemia in infected cats. Depending upon the rate of exposure to infective larvae, the outcome can be reduced hemoglobin levels,
reduced packed cell volume or death. The number of worms recovered from infected cats is usually not high. In one study, a
mean of 100 worms per cat was all that was necessary to cause death in 16 cats.
Apparently A. braziliense is less pathogenic than A. tubaeforme. Experimental infections with A. braziliense have failed to
induce clinical disease similar that described for A. tubaeforme. However, A. braziliense is the hookworm species responsible
for most cases of creeping eruption, a condition characterized by serpiginous dermal lesions in humans following penetration
and migration of hookworm larvae.
Photo 5: Egg of Ancylostoma tubaeforme from fecal flotation.
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Diagnosis of hookworm infection in cats is based on recovery of eggs in fecal flotation preparations (see Photo 5). Although
eggs of A. tubaeforme and A. braziliense are not easily differentiated, the geographic range limitations of A. braziliense
eliminates this problem except for Florida and the Gulf Coast states.
Several products are highly effective against A. tubaeforme or A. braziliense in cats (Table 4). Prevention of predatory behavior
in outdoor cats can reduce levels of infection for hookworms and roundworms, but this is difficult given the strong instinctive
nature of this behavior. Although maintaining cats as entirely indoor pets could reduce the exposure to worm parasites, this
is difficult to achieve in many situations. Periodic or monthly treatment remains the most effective means of controlling
internal parasites. As mentioned above, the latter is more easily justified now that some available products show claims for
prevention or control of heartworm and/or fleas and veterinarians are more likely to use the products to prevent or control
these parasites.
Suggested Reading- Centers for Disease Control, National Center for Infectious Diseases, American Association of Veterinary Parasitologists:
How to prevent transmission of intestinal roundworms from pets to people. Publication No. MS F22, Division of Parasitic Diseases,
Centers for Diseases Control, Atlanta, GA, 1996.
- Kazacos KR: Visceral and ocular larva migrans. Seminars Vet Med Surg (Small Anim) 6: 227-235, 1991.n Spain CV, Scarlett JM,
Wade SE et al: Prevalence of enteric zoonotic agents in cats less than 1 year old in central New York State. J Vet Int Med
15: 33-38, 2001.
- Hill S, Lappin MR, Cheney J, et al: Prevalence of enteric zoonotic agents in cats. J Am Vet Med Assoc 216: 687-692, 2000.
- Olson ME, Ceri H, Morch DW: Giardia vaccination. Parasitol Today 16: 213-217, 2000.
- Feline Clinical Parasitology. DD Bowman (Ed.). Iowa State University Press, Ames, 2002, 469 pp.
- Akao N, Takayanagi TH, Suzuki R et al: Ocular larva migrans caused by Toxocara cati in mongolian gerbils and a comparison
of ophthalmic findings with those produced by T. canis . J. Parasitol. 86: 1133-1135, 2000.
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