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Small Animal Flukes. Nanophytes salmincola

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Presentation Transcript
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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 Neorickettsiahelminthoeca 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.

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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 .

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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.

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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.

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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.

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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".

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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

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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.

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Clinical Signs and History

Dog before infection

Dog 9 days after infection

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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.

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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.

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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 peyer’s patch visible from the serosal surface of intestine.

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Pathology

Enlarged mesenteric lymph nodes.

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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.

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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).

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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.

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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.

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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.

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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.

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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 .

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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.

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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.

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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 182:172, 19.

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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.

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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.

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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. 69:912-917).

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Egg of Alaria canis

Operculated eggs are large and oval. They measure 117-126 m by 74-78 m. Treatment is unknown.

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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".

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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 .

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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

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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).