Heterophyes heterophyes and Metagonimus yokogawai are presented together as so many similarities exist between the two parasites. The two parasites are easily confused but a distinguishing factor is that they are found in different geographic locations of the world. H. heterophyes, an organism that causes a disease known as heterophyiasis, is found primarily in both the Near and Far East as well as parts of Africa. M. yokogawai is found in Asia and Siberia and is known as the causative agent for the disease metagonimiasis. The two organisms are predominantly found as cat and dog parasites, as well as other fish-eating mammals, so heterophyiasis and metagonimiasis are known as zoonoses (animal related) when they infect humans. Minute teardrop-shaped flukes found in the small intestines of fish-eating birds and mammals. The eggs of H. heterophyes and M. yokogawai are indistinguishable from each other. They are small flukes known jointly as heterophyids (from the genus comprising these two species) and are approximately 30 μm by 15 μm. The eggshells of M. yokogawai appear to be thinner than those of H. heterophyes, although this can only be determined by close microscopic attention. The mature flukes of both species are approximately 1 to 2 mm in length. The adult flukes live burrowed between the villi of the host's small intestine  It only takes around 4 to 6 hours for H. heterophyes to get to the small intestines in the definitive host and even faster in hosts that it does not prefer. The eggs that are laid contain a miracidium but do not hatch until they are ingested by a snail (Cerithideopsilla conica in Egypt or Cerithidia cingula in Japan). Inside the snails gut, the miracidium becomes a sporocyst which then begin to produce rediae. The rediae produce cercariae which then exit the snail, swim toward the surface of the water, and slowly fall back down. On their way down, they contact a fish and penetrate into the epithelium of the fish. Here, the cercariae encyst in the muscle tissue. The second intermediate host include freshwater fish: Mugil cephalus, Tilapia nilotica, Aphanius fasciatus, and Acanthogobius sp.  The definitive host, such as humans or birds, eats the undercooked or raw meat of a fish and ingest the parasite. Natural definitive hosts are cats, dogs, foxes, wolves, pelicans, and humans.Each worm causes a mild inflammatory reaction at its site of contact with the intestine. Heavy infections which are common cause damage to the mucosa and produce intestinal pain and are associated with diarrhea, mucus-rich feces, pain, dyspepsia, anorexia, nausea and vomiting.

1. HETEROPHYES
HETEROPHYES
By
IYUMVA AIMABLE
2014-BNS-FT-031
To
afayoarbt@gmail.com

2. Heterophyes
heterophyes• Heterophyes heterophyes and Metagonimus yokogawai are presented
together as so many similarities exist between the two parasites. The
two parasites are easily confused but a distinguishing factor is that
they are found in different geographic locations of the world.
• H. heterophyes, an organism that causes a disease known as
heterophyiasis, is found primarily in both the Near and Far East as well
as parts of Africa.
• M. yokogawai is found in Asia and Siberia and is known as the
causative agent for the disease metagonimiasis.
• The two organisms are predominantly found as cat and dog parasites,
as well as other fish-eating mammals, so heterophyiasis and
metagonimiasis are known as zoonoses (animal related) when they
infect humans.

3. Morphology
• Minute teardrop-shaped flukes found in the small
intestines of fish-eating birds and mammals.
• The eggs of H. heterophyes and M. yokogawai are
indistinguishable from each other. They are small flukes
known jointly as heterophyids (from the genus comprising
these two species) and are approximately 30 μm by 15 μm.
• The eggshells of M. yokogawai appear to be thinner than
those of H. heterophyes, although this can only be
determined by close microscopic attention. The mature
flukes of both species are approximately 1 to 2 mm in
length.

4. Life cycle

6. Life Cycle
• The adult flukes live burrowed between the villi of the host's small
intestine
• It only takes around 4 to 6 hours for H. heterophyes to get to the
small intestines in the definitive host and even faster in hosts that it
does not prefer.
• The eggs that are laid contain a miracidium but do not hatch until they
are ingested by a snail (Cerithideopsilla conica in Egypt or Cerithidia
cingula in Japan).
• Inside the snails gut, the miracidium becomes a sporocyst which then
begin to produce rediae.
• The rediae produce cercariae which then exit the snail, swim toward
the surface of the water, and slowly fall back down.

7. • On their way down, they contact a fish and
penetrate into the epithelium of the fish.
• Here, the cercariae encyst in the muscle tissue.
• The second intermediate host include freshwater
fish: Mugil cephalus, Tilapia nilotica, Aphanius
fasciatus, and Acanthogobius sp.
• The definitive host, such as humans or birds, eats
the undercooked or raw meat of a fish and ingest
the parasite. Natural definitive hosts are cats, dogs,
foxes, wolves, pelicans, and humans.

8. Epidemiology
• People at high risk for infections are those who live by bay waters
including fishermen.
• Infection is acquired by eating raw fish, a common food in areas
of heavy endemicity.
• In endemic areas, people who live near lake shores or river banks
usually have a higher rate and intensity of infection than those
living a distance from such areas.
• It is possible that inhabitants of these areas eat more low-salted
or improperly cooked fish and that their fish are obtained
from polluted water.
• It is common practice for people to defecate on the lake shores
and river banks or from their boats while fishing. In rural areas of
Egypt there was a higher chance of being infected with H.
heterophyes due to being a lower socioeconomic area and not
having easy access to medical services.

9. Adult Egg

10. Pathology
• Each worm causes a mild inflammatory reaction at
its site of contact with the intestine.
• Heavy infections which are common cause damage
to the mucosa and produce intestinal pain and are
associated with diarrhea, mucus-rich feces, pain,
dyspepsia, anorexia, nausea and vomiting.

11. Cont’
• Sometimes eggs can enter the blood and lymph
vascular systems through mucosa go into
the ectopic sites in the body.
• The heart can be affected with tissue reaction in
the valves and myocardium that cause heart failure.
• Eggs can also get into the brain or spinal cord and
cause neurological disorders

12. Disease Transmission
• Transmission of either of these two diseases
happens when uncooked or inadequately cooked
fish are eaten.
• The eggs of H. heterophyes and M. yokogawai may
be confused with those of the liver fluke Clonorchis
sinensis.
• Adult worms of these species are almost never
detected in fecal waste.

13. Laboratory Diagnosis
• Because the adult fluke is almost never seen in a fecal
specimen, the presence of eggs provides the diagnostic
tool for determining infection.
• When seen, the adult stages of both species are tiny,
measuring 1 to 2 mm in length.
• The diagnosis of either heterophyiasis or metagonimiasis is
most often accomplished by detecting the characteristic
ova during a routine examination for ova and parasites in a
stool specimen.

14. Cont’
• The ova must be differentiated from those of
Clonorchis sinensis, because the eggs of H.
heterophyes and M. yokogawai are indistinguishable
from each other.
• However, purported differences in the thicknesses of
the egg shells of the two species may be possible, but
differentiation of the two species is merely academic,
as the treatment is the same for either species.

15. General Classification Heterophyid Eggs
organisms Heterophyes heterophyes and Metagonimus
yokogawai
Specimen required feces
stage egg
Size and shape 30×90 µm Oval and contains a formed
miracidium
shell Thin and smooth ( shell of M. Yokogawai
thinner)
Other features Eggs are operculated
and have shoulders
near the operculum;
sometimes there is a
small boss (protuberance)
opposite the
operculum

16. Geographical Distribution and
Epidemiology
• H. heterophyes have been reported in Egypt, Sudan, Iran,
Turkey, Tunisia, China, Taiwan, the Philippines, Indonesia,
Africa and India.
• In one Egyptian village, the highest prevalence of infection,
37%, was found among individuals aged 15-45 years, greater
for females than males, followed by 28% prevalence in
children 5 years of age. Over 10,000 people are estimated to
be infected in Egypt.
• H.heterophyes in China occurs in approximately 230,000
infected people.

17. • M. yokogawai is mainly distributed in China, Japan, Korea,
Taiwan, Indonesia, Russia, Israel, the Balkans and Spain.
• An estimated 500,000 people are infected in South Korea,
150,000 in Japan and 12,000 in Russia. Epidemiologic
studies have compared prevalence of food-borne trematode
infections in villages close to water bodies and found a
relative risk of 5.01 to 7.44 in Republic of Korea for
M.yokogawai infection associated with proximity to fresh
water.
• Twenty-fi ve percent of food fi shes like perch and mullet
studied from Jinju Bay, Korea, were infected with
heterophyid metacercaria.

18. Treatment and Prevention
• As for a number of other trematodes, praziquantel
is the choice for treatment of infections from both
H. heterophyes and M. yokogawai.
• Proper disposal of human wastes is paramount in
preventing the diseases, where water runoff into
bodies of water is controlled.
• Thoroughly cooking fish, especially those from
endemic areas of the world, will also minimize the
number of cases of infection by H. heterophyes and
M. yokogawai.

19. References
• https://en.wikipedia.org/wiki/Heterophyes_hetero
phyes
• Chai J. Y., Darwin Murrell K. & Lymbery A. J. (2005).
"Fish-borne parasitic zoonoses: Status and
issues". International Journal for
Parasitology 35(11-12): 1233-1254.
• parasitology for medical and clinical laboratory professionals
by John W. Ridley, Ph.D.