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150 CHAPTER 6

brownish-yellow tint, and have a thin transparent hyaline
Source: Centers for Disease Control and Prevention (CDC) unsegmented ovum. During its passage down the intes-
shell membrane that is not normally bile stained. When
released by the worm in the intestine, the egg contains an

tine, the ovum develops and thus the eggs passed in feces
have a segmented ovum, usually with 4 to 8 blastomeres.
Because the similarity of the ova of both agents is
so strong, a report of “hookworm ova” is sufficient with-
out differentiating between the two species. S. stercoralis

so the differentiation between hookworm and S. ster-
coralis must be made. In a number of parasitic infec-
tions, blood tests in early infection often show a rise in
FIGURE 6-11 Hookworm (L), and a Strongyloides (R) hookworm larvae require an entirely different treatment,
filariform infective stage larvae numbers of eosinophils, a type of white blood cell that
is preferentially stimulated by worm infections in tissues
(large numbers of eosinophils are also present in the local
with each other, especially because both are contracted inflammatory response). Falling blood hemoglobin levels
in the same manner, from contaminated soil. It may be will be seen in cases of prolonged infection with some-
important to differentiate between the two filariform lar- times severe anemia as well as a general appearance of
vae (Figure 6-11). illness and perhaps a loss of weight. The victim is often
An interesting consequence of Ancylostoma duode- listless from the anemic condition and presents a picture
nale infection is that of translactational transmission of of generally poor health when infected by large popula-
the infection in humans where a breast-feeding mother tions of hookworm parasites.
passes the infection to the infant. The larvae are able to Differentiation of species between A. duodenale and
pass into the mammary glands of the mother, so that the N. americanus requires the presence of the rhabditiform
newborn baby can receive a large dose of infective larvae larvae as well as other factors (Table 6-1). Sometimes the
through its mother’s milk. This possibly explains cases ova hatch in the feces and both ova and larvae will be found
of heavy and sometimes fatal hookworm infections in in a fecal sample. Distinguishing features for differentiation
children a month or so of age, in places such as China, of species is made by the morphology of the buccal capsule
India, and in other more isolated population groups that and presence of copulatory bursa in the male. The buccal
include the aborigines of northern Australia. Ancylostoma capsule of A. duodenale is equipped with teeth, whereas
caninum, a related organism, also causes infections in that of the N. americanus reveals cutting plates. Three
dogs. The organisms may be passed through the milk of developmental stages of hookworm larvae are as follows:
the mother dog and the newborn pups may even die of
1st stage—the rhabditiform larva is the free-living form
hemorrhaging from their intestines. This phenomenon
may lend credence to those who associate parasitic infec- 2nd stage—filariform larvae not capable of indepen-
tions of similar organisms in both domestic animals and dently living in the environment and must find a host;
humans as confirming a close evolutionary link between possess shorter esophagus than that of the rhabditi-
some species of human and canine parasites. form larvae
3rd stage—infective form capable of penetrating the
Laboratory Diagnosis skin through contact with soil

Recovery of ova (eggs) or larvae may not be possible in Treatment and Prevention
the early stages of the infection, until the disease has pro-
gressed to a more advanced stage. Diagnosis depends Topical solutions for treatment of dogs and cats are avail-
on finding characteristic worm eggs on microscopic ex- able, a critical component of preventing the disease from
amination of the stools. The eggs are oval or elliptical and being contracted by humans. It utilizes moxidectin for
measure roughly 60 μm by 40 μm, are colorless with a control and prevention of roundworms, hookworms,