Hammondia hammondi Frenkel 1974
ETYMOLOGY: Hammondia after Dr. Datus M. Hammond and hammondi after Dr. D. M.
SYNONYMS: Toxoplasma hammondi [Frenkel, 1974] Levine 1977; Isospora hammondi
[Frenkel and Dubey, 1975] Tadros and Laarman, 1976. Hammondia hammondi was also refereedto as the CR-4 strain of Toxoplasma gondii isolated by Frenkel and Dubey (1975A, 1975B) and
the WC1170 parasite of Wallace (1973).
HISTORY: The oocysts of this parasite are structurally indistinguishable from those of
Toxoplasma gondii. In 1971, Drs. Frenkel and Dubey isolated oocysts that were structurally
similar to T. gondii from a feral cat from Iowa. Dr. Wallace (1973) also isolated a similar
parasite from the feces of a feral cat from Hawaii. Inoculation of mice with these oocysts
produced large tissue cysts in skeletal muscles and very few tissue cysts in the brain. Both
groups of researchers demonstrated that the life cycle of the parasite is heteroxenous. Dr. Frenkel
first erected the Genus Hammondi and used the name H. hammondi in a review article on tissue
cyst forming coccidia (Frenkel, 1974). He and Dr. Dubey latter fully described the life cycle of
the parasite (Frenkel and Dubey, 1975a, 1975b). Because he published the name first (Frenkel,
1974) he is technically the author of the original name Hammondia hammondi and not he and
Dr. Dubey as is frequently cited.
GEOGRAPHIC DISTRIBUTION: Probably worldwide. Hammondia hammondi has been
found in Iowa and Hawaii in the United States (Frenkel and Dubey, 1975a, 1975b; Wallace,
1975), Germany (Rommel and Seyerl, 1976), Australia (Mason 1978) and Japan (Shimura and
PREVALENCE: The prevalence of infection in cats is low. Wallace (1975) found H. hammondi
in 3 of 1,604 cats in Hawaii. Christie et al. (1977) examined the feces form 1,000 cats in
Columbus, Ohio for H. hammondi. Nine cats were shedding oocysts which were the correct size
and shape for either H. hammondi or T. gondii. Two of these proved to be H. hammondi and 7
were T. gondii following mouse inoculation. Another isolate of H. hammondi was obtained from
a pooled sample from 175 cats by mouse inoculation.
PARASITE IDENTIFICATION: Oocysts of H. hammondi are excreted unsporulated in the
feces. The oocysts are colorless, subspherical to spherical, and measure 10.5-12.5 by 11.2-
13.2 &m (mean, 10.6 by 11.4 &m). Sporulated oocysts contain two ellipsoid sporocysts each
with 4 sporozoites. Sporocysts measure 6.0-7.5 by 8.0-10.7 &m (mean, 6.5 by 9.8 &m), lack
a Stieda body, and contain a sporocyst residuum composed of dispersed or compact granules.
The sporozoites are elongate and curved within the sporocyst had have a crystalloid body.
Sporulation occurs in 2 to 3 days at room temperature (22 to 26 C).
The similarity in oocyst size and structure between T. gondii and H. hammondi make
diagnosis based on oocyst structure alone impossible. Animal inoculation is needed for a
definitive diagnosis to be obtained. Identification of H. hammondi in tissues is also difficult. The
tachyzoites of T. gondii and H. hammondi are indistinguishable from each other. The tissue cysts
of H. hammondi resemble those of T. gondii and can be confused with sarcocysts of some thin-
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walled Sarcocystis species (Mehlhorn and Frenkel 1980).
LIFE CYCLE: Cats are the only know feline definitive hosts. However, other felids may be
suitable definitive hosts. The life cycle is obligatorily heteroxenous. Two types of schizonts are
found in the cats small intestines 4 and 5 days after tissue cysts are ingested. The sexual stages
first appear 5 days after infection. The prepatent period is 5 to 6 days and the patent period is 12
to 28 days. Inoculation of cats with H. hammondi oocysts does not lead to oocyst excretion or to
latent infections in their tissues.
Natural intermediate hosts include rats (Rattus rattus and R. norvegicus), goats (Capra
hircus), and roe deer (Capreolus capreolus). Experimental intermediate hosts include white
mice, deer mice, long-tailed field mice, yellow-necked field mice, rats, multimammate rats,
guinea pigs, hamsters, bank voles, European voles, field voles, dogs, goats, sheep, monkeys, and
pigs (Dubey, 1993). Chickens can not be infected with H. hammondi (Dubey and Streitel, 1976).
When an intermediate host ingests oocysts of H. hammondi, the oocysts excyst in the intestine
and liberate the sporozoites. The sporozoites penetrate the intestinal mucosa and multiply by
endodyogeny in the lamina propria, submucosa and muscularis, Peyer's patches and mesenteric
lymph nodes for about 11 days. Tissue cysts are present in the muscles of mice by 11 days. The
tissue cysts are initially small but can be over 300 &m in length in about a month. The tissue
cysts remain viable for 1.3 years and probably longer. Tissue cysts are not infective for
intermediate hosts. Congenital transmission of H. hammondi does not occur in mice (Dubey and
Streitel, 1976) or cats (Dubey, 1977).
PATHOGENICITY: Hammondia hammondi does not cause disease in cats. Mice inoculated
tracts of these mice and are due to multiplication of tachyzoites. A transient myositis may be
present in the skeletal muscles of infected mice.
IMMUNITY: Immunity to H. hammondi in cats is less stable than immunity to T. gondii.
About 50% of cats will re-excrete oocysts when challenged (Dubey, 1975). Some cats
will spontaneously re-excrete small numbers of oocysts in the absence of reinfection.
Immunosuppression of cats does not affect the course of a primary H. hammondi infection in
cats but does cause cats to re-excrete oocysts. Infection with H. hammondi does not make cats
immune to infection with T. gondii. Cats that have recovered from a H. hammondi infection do
not develop antibodies to T. gondii.
In contrast to cats, intermediate hosts that are inoculated with oocysts develop antibodies
that cross-react with T. gondii. This cross-reactive immunity is also protective against challenge
with pathogenic strains of T. gondii (Christie and Dubey, 1977; Dubey, 1978; 1981; Monday and
Dubey, 1988). Hammondia hammondi immune serum from mice recognizes all the major
surface antigens of T. gondii except the 21.5 kD antigen (Araujo et al., 1984). A monoclonal
antibody to the immunodominant p30 antigen of T. gondii also reacts with tachyzoites of H.
hammondi (Riahi et al., 1998). Immunization of hamsters with H. hammondi affords minimal
protection against challenge with Besnoitia jellisoni (Dubey, 1978).
HAZARDS TO HUMANS: Hammondia hammondi infection was attempted in 4 species
of nonhuman primates (Saguinus nigricollis, Macaca fascicularis, Macaca mulatta, and
Cercocebus atys) (Dubey and Wong, 1978). None of the monkeys developed clinical signs of
oocysts may suffer from up to 30% mortality. Lesions are present in the intestinal
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disease and H. hammondi was isolated from only Saguinus nigricollis. It is possible that humans
could serve as intermediate hosts. No recorded cases of human infection exist.
Araujo FG, Dubey JP, Remington JS. 1984. Antigenic similarity between the coccidian
parasites Toxoplasmagondii and Hammondia hammondi. J Protozool 31:145-147.
Christie E, Dubey JP. 1977. Cross-immunity between Hammondia hammondi and
Toxoplasma infections in mice and hamsters. Infect. Immunol. 18:412-415.
Christie E, Dubey JP, Pappas PW. 1977. Prevalence of Hammondia hammondi in the feces
of cats in Ohio. J. Parasitol. 63:929-931.
Dubey JP. 1975. Immunity to Hammondia hammondi infection in cats. J Am Vet Med
Dubey JP. 1993. Toxoplasma, Neospora, Sarcocystis, and other tissue cyst-forming coccidia
of humans and animals. In Parasitic Protozoa, Vol. 6., J.P. Kreier and J.R. Baker
(eds), Academic Press, Inc., San Diego, Calf. pp 1-158.
Dubey JP. 1977. Attempted transmission of feline coccidia from chronically infected
queens to their kittens. J Am Vet Med Assoc 170:541-543.
Dubey JP. 1978. A comparison of cross protection between BCG, Hammondia
hammondi, Besnoitia jellisoni and Toxoplasma gondii in hamsters. J Protozool 25:382-
Dubey JP. 1981. Prevention of abortion and neonatal death due to toxoplasmosis by
vaccination of goats with the nonpathogenic coccidium Hammondia
hammondi. Am J Vet Res 42:2155-2157.
Dubey JP, Steitel RH. 1976. Further studies on the transmission of Hammondia hammondi
in cats. J Parasitol 62:548-551.
Dubey JP, Wong M. 1978. Experimental Hammondia hammondi infection in monkeys. J
Parasitol 64:551-552.
Frenkel JK. 1974. Advances in the biology of sporozoa. Z Parasitenkd. 45:125-162.
Frenkel JK, Dubey JP. 1975a. Hammondia hammondi gen. nov., sp.nov., from domestic
cats, a new coccidian related to Toxoplasma and Sarcocystis. Z Parasitenkd 46:3-12
Frenkel JK, Dubey JP. 1975b. Hammondia hammondi: A new coccidium of cats producing
cysts in muscle of other mammals. Science 189:222-224.
Mason RW. 1978. The detection of Hammondia hammondi in Australia and the
identification of a free-living intermediate host. Z Parasitenkd 57:101-106.
Mehlhorn H, Frenkel JK. 1980. Ultrastructural comparison of cysts and zoites of
Toxoplasma gondii, Sarcocystis muris, and Hammondia hammondi in skeletal muscle of
mice. J Parasitol 66:59-67
Munday BL, Dubey JP. 1988. Prevention of Toxoplasma gondii abortion in goats by
vaccination with oocysts of Hammondia hammondi. Aust Vet J 65:150-153.
Riahi H, Bouteille B, Darde ML. 1998. Antigenic similarity between Hammondia hammondi
and Toxoplasma gondii tachyzoites. J Parasitol 84:651-653.
Rommel M, von Seyerl F. 1975. 1st demonstration of Hammondia hammondi (Frenkel and
Dubey 1975) in the feces of a cat in Germany. Berl Munch Tierarztl Wochenschr 89:398-
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Shimura K, Ito S. 1986. Isolation of Hammondia hammondi in Japan. Nippon Juigaku
Wallace GD. 1973. Sarcocystis in mice inoculated with Toxoplasma-like oocysts from cat
feces. Science 180: 1375-1377.
Wallace GD. 1975. Observations on a feline coccidium with some characteristics of
Toxoplasma and Sarcocystis. Z Parasitenkd 46:167-178.