Small Animal Flukes

1
Small Animal Flukes
2
Nanophytes salmincola Life Cycle There are 32
known natural and experimental hosts for
Nanophytes. Most of these are wild or domestic
fish-eating mammals (i.e. , raccoon, bear, lynx,
fox, dog, etc.), but three species of fish-eating
birds can also complete development of the fluke.
Although the fluke can develop in all these
species of animals, only the dog and other
members of the Canidae such as the fox and coyote
are susceptible to Neorickettsia helminthoeca,
the "salmon poisoning" agent, that the fluke
carries. A second rickettsia-like agent which is
serologically distinct from Neorickettsia
helminthoeca is also transmitted by Nanophyetes
to dogs and acts synergistically with it to
produce clinical disease. This agent is at
present known as the "Elokomin fluke fever
agent". Since a generic name has not yet been
assigned these two agents generally occur
together in dogs to form the "Salmon poisoning
disease complex", although the Elokomin fluke
fever agent has been isolated singly from
naturally infected dogs.
3
Eggs are shed in the feces of the definitive host
and undergo further maturation and development in
water. After 90 days, ciliated, free swimming
miracidium emerge from the operculated end of the
ova which have about 24 hours to find and
penetrate the snail intermediate host, Goniobasis
plicifera. After penetrating into the snail,
development of asexually reproducing larval
stages begins -- the miracidia becomes a
sporocyst, the sporocyst gives rise to mother
rediae, and the mother rediae produce daughter
rediae. Daughter redia produce stub-tail cercaria
which the snail sheds into the water. Cercaria
can either penetrate one of the fish secondary
intermediate hosts directly through the skin upon
contact, or they can be ingested. Either way, the
cercaria migrate to deeper tissues via the
circulatory system and encyst as metacercaria.
After 10 days, the metacercaria are infective for
the final host. Salmon are the principle fish
intermediate host for Nanophyetus although trout,
steelhead and the Pacific giant salamander can
also be infected. Once in the definitive host,
metacercaria hatch in the intestinal tract, and
young flukes attach to the mucosa. A rapid
maturation of the fluke occurs and in 5- 7 days
ova again appear in the feces .
4
Goniobasis plicifera
Goniobasis plicifera, the snail intermediate host
for Nanophyetus. These small aquatic snails are
found in most of the creeks, streams and rivers
of the endemic area in the Pacific Northwest.
5
Geographic Distribution of Goniobasis
Since the fluke develops in only this species of
snail, the distribution of the snail restricts
both the fluke and the salmon poisoning agent the
fluke carries to this same general area. Only
fish which have spent some phase of their life
within the endemic area can carry the salmon
poisoning agent.
6
Salmon caught in the coastal waters of the
Pacific Northwest
Salmon or steelhead can be infected with cercaria
either during migration to spawning grounds as
adults or during migration to the ocean from
inland spawning grounds as young
fish. Metacercaria and the Neorickettsia agent
have been shown to remain viable in ocean going
salmon for 33 months. Therefore, both ocean
caught and fresh water caught salmon from the
endemic area can cause "salmon poisoning" if
eaten by a dog.
7
Since the Neorickettsi helminthoeca agent is
almost ubiquitous in metacercaria and all other
stages of the fluke life cycle, it becomes
apparent that if a dog ingests raw salmon,
steelhead, or trout from the endemic area during
the late summer and fall, he has an extremely
good chance of developing "salmon" poisoning
disease".
8
Histosection of salmon kidney with two
metacercaria
Kidney tissue is heavily infected in salmon.
Although distribution of metacercaria in various
body sites varies with different fish species,
all parts of the fish host should be considered
infected if ingested. Ingested metacercariae
excyst and attach to the intestinal mucosa
9
Adult Nanophyetus as a stained specimen showing
internal structures
Nanophyetus is a very small fluke (up to 1.5 by 5
mm). Adult flukes inhabit the small and large
intestine and are found in close association with
the intestinal mucosa. The fluke is almost
innocuous and causes very little pathology by
itself. It is significant as a parasite because
it carries Neorickettsia helminthoeca.
10
Clinical Signs and History
Dog before infection
Dog 9 days after infection
11
Clinical Signs and History
Disease is characterized by 1. An incubation
period of 5- 7 days after ingestion of fish. 2. A
rise in body temperature to 103-107F occurs for
about 3-4 days and then drops back to
normal. 3. Complete anorhexia. 4. Diarrhea and
vomiting diarrhea becomes bloody in very
severe or fatal cases . 5. Conjunctival
exudate. 6. Enlargement of palpable lymph
nodes 7. Rapid weight loss, dehydration and death
in 10-14 days. Mortality is 50-90 in untreated
cases. The clinical signs of salmon poisoning
should be differentiated from distemper.
Recovered animals are immune to the Neorickettsia
but can be reinfected with the fluke.
12
Typical diarrhea of salmon poisoning
Initially diarrhea is yellowish and small in
quantity -- Later in the disease in severe cases
the diarrhea may become hemorrhagic.
13
Pathology
Neorickettsia helminthoeca causes a generalized
disease of the reticuloendothelial system.
Pathology would include enlargement of all lymph
nodes of the body, splenic enlargement, and
enlarged peyer's patches. Reticuloendothelial
tissues in the thymus, liver, and other organs
also are affected and the Neorickettsia agent is
recoverable from these tissues. An enteritis from
the pylorus to anus occurs and is of a catarrhal
or hemorrhagic nature.
Enlarged peyers patch visible from the serosal
surface of intestine.
14
Pathology
Enlarged mesenteric lymph nodes.
15
Nanophyetus salmincola egg
Diagnosis is based on history of eating uncooked
fish, clinical signs and finding typical eggs
upon stool examinations.
Eggs are 97 x 60 in size, light brown in color,
rough shelled, and have an indistinct operculum
at one end.
16
Lymph node aspirate (Giemsa stain) showing
clusters of Neorickettis helminthoeca elementary
bodies in the cytoplasm of the phagocytic cells
of the reticuloendothelial system.
A diagnosis of Salmon poisoning can be supported
by examining lymph node (i. e. mandibular or
prescapular) aspirates for Neorickettsia
elementary bodies. (The agent can be recovered
for several months after recovery, however.) Eggs
appear in the feces in 5- 7 days post-infection
and are usually present after the febrile period
of disease. The presence of eggs does not
necessarily indicate active Neorickettsia
infection (i.e. flukes in immune animal).
17
Treatment and Control
Treatment with tetracycline for at least three
days is effective against the agent.
Sulfonamides, penicillin, and chloramphenicol are
also effective. Supportive measures include fluid
therapy and blood transfusion if necessary
antibacterial, anticholinergic drugs and bland
high carbohydrate diets are used to combat severe
diarrhea. Early treatment is important and if
treatment is begun in the early febrile period,
other signs are greatly diminished or never
appear. Treatment is effective and most dogs can
be saved with proper therapy. Practitioners in
the endemic area sometimes deliberately infect
and treat dogs to produce immunity with naturally
infected fish. Although salmon poisoning is not
highly contagious, aerosol and contact
transmission between dogs can occur and infected
dog should be isolated. Prevention involves not
allowing dogs access to raw fish within the
endemic area (i.e. fishing trips). Cooking
destroys the infective agent but the agent can
survive freezing and smoking.
18
Heterobilhazia americana (canine schistosomiasis)
Heterobilharzia americana has a life cycle and
morphology typical of the Family
Schistosomatidae. This group of trematodes
includes highly pathogenic schistosomes of man,
Schistosoma mansoni, S. haematobium, and S.
japonicum. Members of this family inhabit blood
vessels of the host and differ from other flukes
in several important respects. They are elongate
and they are unisexual rather than
hermaphroditic. They exhibit sexual dimorphism
and usually occur in pairs (as seen here). The
female in the gynocophoral groove, a ventral,
gutter-like canal formed by the uncurbed lateral
margins of males body. The suckers are weak and
close together or absent.
19
H. americana in the mesenteric veins of a dog
Heterobilharzia was first reported in a dog from
Louisiana in 1961 and has since been reported in
a dog from East Texas. It had been reported
previously in certain wild animals in the
Southeastern U.S., including the racoon, bobcat,
nutria, and rabbit. The adult fluke occurs in the
mesenteric, portal, and hepatic veins.
20
Fork-tailed cercariae
Aquatic snails Lymnaea. Pseudosuccinea) are the
first intermediate hosts. After infection by free
swimming miracidia, cercariae (shown here) are
ultimately released which infect the final host
by direct penetration, either through the skin or
by drinking water containing cercariae. A
metacercaria form is absent in schistosome life
cycles. Cercariae shed their tail at penetration
and become a migrating-"schistosomule".
Schistosomules migrate to the lungs (5-9 days),
thence to the liver (7-45) days and finally to
the small mesenteric veins and intra-hepatic
portal veins where they develop to patency at
about 10 weeks after infection.
21
Egg of Heterobilharzia americana
Eggs are large, oval and measure 87m by 70m. When
passed in the feces each contains a mature
miracidium which hatches immediately after
contact with water .
22
Eggs in intestinal wall
Eggs find their way to the feces by passing
through the vessel and intestinal walls into the
intestinal lumen. This is thought to be aided by
histolytic secretions of the embryo.
23
Although most eggs are shed in the feces, many
are swept to the liver and sometimes other sites
in the blood. Thrasher (JA VMA 14.4 1119-1126)
reported on results of experimental
Heterobilharzia infections in the dog in 1964.
The livers of infected dogs were enlarged and
pale with diffuse multifoca1 yellow foci of 1-2mm
in size. Histologically eggs infiltrated in the
portal triads with resulting granulomatous
inflammation and portal fibrosis. Splenomegaly
and petechial hemorrhage in the lungs were also
observed. Eggs havean important role
in pathogenesis.
24
Clinical Signs and Diagnosis
Clinical signs of Heterobilharzia in the dog
consist of chronic, intermittent, mucoid diarrhea
and progressive emaciation. Other signs were not
seen in the limited number of cases reported for
the dog although it is probable that eventual
cirrhosis of the liver might develop in long
standing infections. Finding the distinctive eggs
in feces provide the only practical diagnostic
method. Standard flotation methods cannot be used
for diagnosis since eggs hatch upon contact with
water . Saline sedimentation is an acceptable
method. Heterobilharzia is considered to be of
minor importance, but in light of the need for
unique diagnostic methods, it may be a more
important disease than has been reported,
particularly in hunting dogs in the coastal
wetlands of Louisiana and the Mississippi delta
where conditions are ideal for transmission.
Treatment with FBZ at 40 mg/kg SID for 10 days is
reported to be effective. Praziquantel is also
likely to be effective since it is used as the
drug of choice to treat human schistosomiasis.
Ref. Ronald and Craig JAVMA 182172, 19.
25
Alaria spp.
Alaria spp. occur in the small intestine of dogs
and less frequently the cat. It is not considered
pathogenic and is of little importance except as
a rare incidental finding at necropsy or finding
the egg at fecal examination.
26
Alaria attached to the small intestine of a dog
Despite a long migration through the abdominal
and thoracic cavities with a return to the gut
via the lungs and trachea, this genus is not
recognized as a pathogen. Alaria has a complex
life cycle. Dogs or cats are infected by
ingestion of the amphibian second intermediate
host or by one of the many paratenic hosts of
this fluke (reptiles, birds, or mammals).
Transmammary infection has recently been
demonstrated for A. marcianae in cats.
27
Stained Adult Alaria
Alaria has a characteristic morphology. It is a
small, whitish fluke 2 to 6mm in length and is
divided in two by a constriction which give the
anterior end a winged appearance. Small ear-like
tentacles occur on these wings. Three human cases
of larva migrans due to the Alaria larval
mesocercariae stage, including one case where
larva were found in the subcutaneous tissues of a
Louisiana man. Zoonotic infections are thought to
occur by either ingestion of undercooked infected
paratenic hosts (man then becomes a paratenic
host also ) or by penetration of mesocercariae
through wounds or mucous membranes while handling
infected animals (i.e. bullfrogs, alligators,
etc). (Ref Shoop WL and KC Corkum. 1983. I.
Parasit. 69912-917).
28
Egg of Alaria canis
Operculated eggs are large and oval. They measure
117-126 m by 74-78 m. Treatment is unknown.
29
Platynosomum fastosum
This liver fluke is a member of the family
Dicrocoeliidae and shares many similarities with
Dicrocoelium. It has been reported from cats in
the Carribean Islands, Florida and other southern
states in the United States. These flukes inhabit
the bile ducts and gall bladder, where they are
associated with dilation and epithelial
proliferation of bile ducts. In heavy infections,
(500 or more flukes) cats may show anorexia,
vomiting, intermittent diarrhea and jaundice
before death. Light infections are
asymptomatic. Like Dicrocoelium, miracidia are
present in eggs when passed in the feces (eggs
34-50 by 20-35 u). Eggs are ingested by snails,
the first intermediate host, and the lizard
(Anolis) is the second intermediate host.
Infections are common in the Bahamas where the
infection is referred to as "lizard poisoning".
30
Metorchis conjunctis
This trematode occurs in the gall bladder, and
bile ducts of the dog, cat, fox, man and other
fish-eating mammals. In North America, is most
prevalent in Canada and is an important parasite
in sled dogs in the Canadian Northwest. However,
it has been reported from the New England states
and South Carolina. An aquatic snail is the
first intermediate host and a fish, the common
sucker, is the second intermediate host.
Infection of the final host occurs by ingestion
of raw fish. Infection may lead to dilation of
the gall bladder and bile ducts and enlarged nad
turgid liver. Microscopically, there is cirrhosis
and proliferation of the bile ducts. Clinically
there is gradual debilitation accompanied by
ascites. Occasionally, jaundice may occur .
31
Six cases of Amphimerus have recently been found
in cats at LSU 3 at necropsy and 3 clinica1
cases. Two of the latter cats were successfully
treated with praziquantel at 3 times the label
dose (30mg/kg). Amphimerus has been previously
reported from Texas and the Midwest. Small
operculated eggs (3Ox15m) containing a fully
developed miracidia are shed in the feces. These
eggs do not float well and a specialized
formol-ethyl acetate sedimentation test is the
method of choice. It is possible many cases are
being missed by routine methods. Hydrobiid snails
in ponds are infected by ingestion of eggs and
ultimately release cercariae which encyst as
metacercariae under the skin of any of several
cyprinoid fish species (shiners, fathead
minnows). Cats are infected by ingestion of fish.
Amphimerus egg
32
Amphimerus
Adult flukes inhabit the bile ducts and gall
bladder. Debility, liver cirrhosis, cholangitis
and diarrhea have been reported as clinica1
signs. A related fluke, Opistorchis spp.,
commonly infects humans in Northern Asia and
Southeast Asia where it is a major public health
problem. Clonorchis sinensis, the oriental liver
fluke of man, is similar in morphology, effects,
and life cycle. It is unknown if the Amphimerus
sp. found in Louisiana can infect dogs (or man).