Worms and Human Disease

58 Chapter 1
Other Occasional and Rare Humanparasitic
Trematodes
Family Diplostomidae
Alaria americana Hall and Wigdor, 1918,
and A. marcianae (La Rue, 1917) Walton,
1950, are very similar parasites of wild
carnivores and dogs and cats in North
America, in which the anterior portion of
the body is spoon-shaped, with an organ
that secretes proteolytic enzymes. They
have an unusual life cycle. When eggs from
faeces reach water, the miracidia hatch out
and penetrate and multiply in suitable
species of snails (including Heliosoma
spp.). The emerging cercariae develop in
amphibian tadpoles into a larval stage
known as a mesocercaria (midway between
a cercaria and a metacercaria). Frogs and
snakes ingest tadpoles and act as paratenic
hosts. When these are eaten by young
carnivores, metacercariae develop in the
lungs, are coughed up and become adults
in the small intestine in about 20 days.
However, in pregnant animals the mesocercariae
migrate to the mammary glands and
infect the suckling young through the milk,
and adults develop in these (known as
‘amphiparatenesis’). They can also infect
subsequent litters (Shoop, 1994). A fatal
case in Canada occurred in a man who
ingested frogs’ legs while hiking. He was
thought to be suffering from gastric flu but
died 9 days later from extensive pulmonary
haemorrhage and at autopsy was found to
have thousands of mesocercariae in many
tissues. In other cases mesocercariae have
been found in the eye (Smyth, 1995).
Another species in carnivores, A. alata
(Goeze, 1782), has occasionally infected
humans with mesocercariae in the Middle
East. Neodiplostomum (= Fibricola)
seoulensis (Seo, Rim and Lee, 1964) Hong
and Shoop, 1994, a parasite of rats, has
developed to adulthood in the human
small intestine in a few cases in South
Korea and is contracted from eating raw
amphibians or snakes (paratenic hosts).
Diplostomum spathaceum (Rudolphi,
1819) Olsson, 1876, is a cosmopolitan para-
site of birds, with metacercariae in the eyes
of fish, and there have been a few cases of
swimmer’s itch in the former Czechoslovakia,
but more importantly cercariae
have entered the eye and caused cataracts
in the lens.
Family Lecithodendriidae
Phaneropsolus bonnei Lie Kian Joe, 1951,
and Prosthodendrium molenkampi Lie Kian
Joe, 1951, were both discovered in Indonesia
at autopsy and are also present in rural populations
of north-east Thailand and Laos.
Eggs of both species are similar to those
of Opisthorchis and heterophyids, and
insects act as second intermediate hosts.
Phaneropsolus spinicirrus, Paralecithodendrium
obtusum and P. glandulosum are
three other poorly characterized species
commonly found in Thais (Yu and Mott,
1994).
Family Plagiorchiidae
Plagiorchis harinasutai Radomyos, Bunnag
and Harinasuta, 1989, P. javensis
Sandground, 1940, P. muris Tanabe, 1922,
and P. philippinensis Sandground, 1940,
have insects as second intermediate hosts
and have been found in humans in
Thailand, Indonesia, Japan and the
Philippines, respectively.
Family Troglotrematidae
Nanophyetus salmincola Chapin, 1927, is
an intestinal parasite of wild carnivores,
birds and domestic dogs in the Pacific
north of the USA and in Siberia.
Metacercariae encyst in salmonid fishes
and in the USA, in dogs that eat the fish.
Adults cause a haemorrhagic enteritis, with
high fever, anorexia, vomiting and lymphadenopathy
(‘salmon poisoning’), with a
high mortality 10–14 days after infection,
caused by a rickettsia (Neorickettsia
helminthoeca), which is transmitted by the