tapeworms of dogs and cats. "tapeworms" are members of the class cestoda which are...

Tapeworms of

Dogs and Cats

"Tapeworms" are members of the Class Cestoda which are included under the Phylum Platyhelminthes (the flatworms) along with the Class Trematoda (the

flukes). Of the several orders of cestodes which occur as parasites in the animal kingdom, only two are of

veterinary importance, the Order Cyclophyllidea and the Order Pseudophyllidea. Most of the important

cestodes of domestic animals and man are cyclophyllidean tapeworms. Only two

pseudophyllidean genera are of any importance in dogs or cats. Distinct morphological and life cycle

patterns differentiate cyclophyllidean and pseudophylidean tapeworms.

Cyclophyllidean larval stagesThe eggs of cyclophyllidean tapeworms develop within

themselves spherical embryos characterized by the presence of three pairs of claw-like hooks. These embryos are known as

oncospheres or hexacanth embryos. Oncospheres remain passively in the eggs until ingested by a proper intermediate host in which they are destined to develop. The intermediate host may be either a vertebrate or an invertebrate, and the

larval form eventually to develop will be either a cysticercus, coenurus, hydatid, or a cysticercoid. After ingestion of the

egg, the oncosphere will penetrate the gut wall of the intermediate host, migrate to one or more specific organs and

develop into one of the above intermediate stages. This constitutes the infective stage of cyclophyllidean tapeworms, and is dependent upon the species of cestode. Upon ingestion

of either a cysticercus, coenurus, hydatid, or cysticercoid (larval forms) by a final host, the bladder-like structure

disintegrate and only scolices survive. These turn right side out (evaginate), attach themselves to the mucosal lining of the intestine, and grow into mature tapeworms. This occurs within the alimentary canal of the final host, and at this site the mature worm develops and hermaphroditic fertilization

occurs.

Order Cyclophyllidea

Dipylidium caninum is cosmopolitan in distribution and is the most common tapeworm of dogs and

cats. It may also occur in wild carnivores and very rarely may infect man. D. caninum resides in the

small intestine.

Dipylidium caninum

Identification characteristics of tapeworms

Tapeworms that occur as the adult form in dogs and cats may be differentiated from one another

by morphology of the scolex (head) , the neck, the individual segments (proglottides) and

characteristics of the entire strobila (body).

The length of mature D. caninum specimens vary from 5 cm to 70 cm and the scolex is extremely small (1/4 - 1/2 mm in width). As with all cyclophyllidean tapeworms, immature segments "bud off” from the neck, pushing the older segments posteriorly where

they become progressively mature and then" gravid" toward the caudal portion of the strobila.The scolex of Dipylidium caninum has four circular suckers and a mobile, retractable rostellum which is "armed" with a number of small spines. These "hold-fast" organs serve as the means of attachment to the intestinal mucosa with the strobila extending freely into the lumen.

D. caninum scolex

D. caninum - Mature proglottid

Because of the unusual shape of the segments, which resemble cucumber seeds when relaxed in water, D. caninum is often

referred to as the "cucumber worm". The reproductive organs are double in each segment and can be seen grossly as two

dense, whitish areas which terminate at a genital pore on the lateral margin of either side. Tapeworms are hermaphroditic;

both male and female organs occur in each set of reproductive organs.

Dipylidium gravid proglottid

When segments become gravid, the uterus grows and

becomes convoluted and packed with eggs.

Shedding segment diagram

Entire gravid segments are continuously shed from the caudal end of the strobila. They remain motile and are found in the

feces or on the perineal area of the host after having crawled from the anus. Eggs are seldom shed individually, but are

contained in "packets" within mature proglottids. Dipylidium infections are therefore usually diagnosed by identification of

shed proglottids rather than by finding eggs by fecal examination. Segments which dry on the perineum of a dog leads to often observed "rice granules" on dogs infected with

cyclophyllidean tapeworms.

Eggs may be found by preparing "squash preparations" of gravid segments, and are less commonly found upon stool examination. The

membrane surrounding egg packets is derived by "pinching" off a portion of the uterus and contains up

to 20 eggs in a gelatinous matrix.

Egg of Dipylidium

Flea intermediate host

Motile proglottids crawl away from stools or from the perineum to other areas such as bedding in the

host's environment. When dry, proglottids rupture, releasing packets of eggs. Further development

depends on the presence of fleas or biting lice as intermediate hosts.

Flea larva

Infection of fleas is possible only at the larval stage which has biting mouth parts for

feeding on organic matter and debris. By the time the flea has become an adult, the

onchosphere has developed to an infective cysticercoid.

Biting louse

Biting lice (Trichodectes canis) serve as less frequent

intermediate hosts. Onchospheres penetrate into the body cavity of lice or fleas and

develop to infective cysticercoids in about thirty days

Cysticercoids

This larval form has a single depressed, (not invaginated) scolex in a small solid cyst without a cyst cavity. Upon

ingestion by the definitive host (while chewing on fleas), the scolex emerges and the rest is digested off.

Dipylidium caninum reaches maturity in a susceptible dog or cat host in approximately three weeks.

Public health

Dipylidium very rarely may infect man. Approximately 40 cases have been recorded in

the U.S. and nearly all of these have been in children, that accidentally ingest fleas that fall off dogs or cats or possibly as a result of being

licked on the face by a dog which has just crushed an infected flea. Human infections are

not considered pathogenic, although vague intestinal disturbances or colic have been

associated with infections.

Taenia Generalized life cycleA number of species of Taenia occur as adults in the small intestine of dogs and cats. Eggs have a thick striated shell

(embryophore) which surrounds a hexacanth embryo. Taenia life cycles involve a Cysticercus larval stage in one or more

mammalian intermediate hosts and infection of the final host occurs by ingestion. The following table lists important

characteristic of the Taenia species that occur in dogs, cats or man. Taenia saginata and T. solium of man are covered in a

separate handout.

Adult Prime Final Larva Prime Larval

Host Intermediate PredilectionHost Site

T. pisiformis dog Cysticercus Rabbit peritoneum pisiformis

T. hydatigena dog Cysticercus Sheep, Ox, Pig peritoneum tenuicollis

T. ovis dog Cysticercus Sheep muscleovis

T. (Hydadigera) cat Cysticercus Rodents liver taeniaeformis fasciolaris

T. saginata man Cysticercus Ox muscle bovis

T. solium man Cysticercus Pig, manmuscle cellulosae

The intermediate stages of Taenia spp. all have their own generic and specific names because

they were originally supposed to be distinct organisms with their own identities. Only in the past century has their relationship to the adult tapeworms been established, and the special

names have persisted though there is now no real need for them. The practice also persists in the trematodes, where there are many cercariae

whose final form is not known, and which are still designated as belonging to the hypothetical

genus Cercaria.

Taenia pisiformis in situ

Taenia pisiformis occurs in the small intestine and next to Dipylidium caninium, is the most

common tapeworm of dogs in the Southeast. It also occurs in cats, foxes, wolves and related

carnivores. Taenia spp. are more robust tapeworms than Dipylidium and segments are

more rectangular in shape.

The scolex is distinctly larger than Dipylidium and bears four suckers and a rostellum armed

with a double row of hooks arranged in a circular pattern.

T. pisiformis Scolex

The genitalia of Taenia spp. are single in each segment, and the genital pores occur in

irregular alternating sequence on either lateral margin.

T. pisiformis mature segment

Gravid segments contain a branched, convoluted uterus packed with individual eggs. Like Dipylidium and other cyclophyllidean tapeworms, gravid segments detach and are passed in the stool. It is unusual to find eggs in the feces and diagnosis is usually made by finding motile proglottids or dry “rice granules”. Placement of the genital pore on proglottids and finding typical eggs on a “squash preparation” allows identification of Taenia species. Identification of cestode species is necessary to knowledge of the probab1e source of infection and subsequent prevention recommendations.

T. pisiformis gravid segment

Eggs of Taenia spp. are small (about 4Ou) and spherical and the embryophore or shell consists of two layers, an outer vitelline layer which is brown and pitted and an inner chitinous layer . Tne embryophore has a typical radial striation, owing to the presence of cemented hexagonal prisms which form much of its thickness. The oncoshere contains 6 hooks (hexacanth embryo).

Taenia eggs

Rabbits are the most common intermediate host to T. pisiformis; it is found to a lesser extent in rodents and squirrels. Upon ingestion of eggs, the embryophore is digested off and very active onchospheres are carried to the liver via the hepatic portal blood. Here they migrate in the parenchyma for about a month before breaking through the capsule to the peritonium, where they grow to cysticerci. As the name indicates, the larva Cysticerci pisiformis is only pea-sized and usually occurs in bunches in the omenta, mesentery or other serosa1 surface. During the wandering phase in the liver, tissue

damage occurs (similar to juveni1e Fasciola migrations) and a condition called “hepatitis cysticercosa” may result in the intermediate host. Cysticerci become infective in approximately 2 months.

T. pisiformis cysticerci

Cysticerci consist of a single scolex invaginated into a fluid filled bladder.

When ingested by the final host, the scolex everts, the bladder structures are digested

away, the scolex attaches to the mucosa and goes on to maturity .

T. pisiformis cysticerci

The prepatent period before passage of eggs or segments is approximately 2 months.

Bovine intermediate host

Cattle, sheep and swine are the primary

intermediate hosts for Taenia hydatigena. T.

hydatigena is one of the largest Taenia species in dogs and may reach 5

meters in length.

Taenia hydatigena

Oncospheres carried to the liver in the portal blood stream, and wander in the parenchyma for about a

month before they break through G1isson's capsule and attach to the peritoneum. Here they grow singly or in

bunches to very large cysts of 7-8 cm diameters on the abdominal serosal surface, particularly on the omentum and mesentery . Damage due to migration in the liver

may lead to “hepatitis cysticercosa”, as with T. pisiformis in rabbits.

Infection of dogs and closely related carnivores occurs by ingestion of cysticerci in offal from cattle, sheep or pigs. It is not a common parasite in the Southeast. The prepatent period, from ingestion of eggs to passage of gravid proglottids is 2 months as with other Taenia species.

Cysticercus tenuicollis

T. ovis is found in the small intestines of dogs and measures about one meter in length when mature. After ingestion of eggs by sheep or goats, the oncosheres are bloodborne to the musculature. T. ovjs is similar in its development to T. saginata or T. solium, except that the dog, rather than man, harbors the adult tapeworms.

Taenia ovis

T. ovis infections in sheep are referred to as “sheep measles” and are similar in size and morphology to “beef measles” or “pork measles”. The most common sites leat sites of infection are the heart and diaphragm but they occur also in striated muscle anywhere in the body. Little is known regarding the effect on sheep, although one worker produced death experimentally by feeding as few as 10 gravid segments. The major losses due to T. ovis involve condemnation of carcasses at meat inspection.

Farm dogs are of greatest importance in transmitting T. ovis, and this species is restricted mainly to Western USA where most of the sheep and goat industry is found. Again, the prepatent period is 2 months.

T. ovis cysticercus

T. taeniaformis is the most common cestode of cats and is widely distributed throughout the U.S. It may also be found in the small intestines of dogs and related carnivores.

Taenia taeniaformis - cat host

This species has a relatively wide intermediate host range with rats, mice, and also rabbits, squirels, and other rodents being capable of harboring cysticerci. When blood-borne oncosperes arrive in the liver, they do not wander, but develop to encapsulated “strobilocerci” which are infective in about 2 months. Strobilocerci occur tightly packed in pea-sized cysts, embedded inliver tissue. Their identity is revealed upon opening the cysts, when they burst out.

T. taeniaformis strobilocercus I rat liver

The scolex of strobilocerus is not invaginated, and is seperated from a cyst or bladder by a chain of asexual proglottids. Upon ingestion by the final host, the entire larval structure except the scolex is digested off. Tapeworms of this larval type therfore make strobila twice in their life cycles.

Strobilocerci teased from rat liver

The prepatent period of 16 to 18 days before passage of gravid segments or eggs is short as

compared to other members of the genus.

T. taeniaformis egg

Multiceps spp. are basically similar to Taenia in life history except that the larval stage is a coenurus. A coenurus differs from a cysticercus only by the presence of

several scolices (rather than one) invaginated from its wall. Some authorities include Multiceps spp. in the genus Taenia. Key characteristics of the two

Multiceps species of dogs are as follows.

Multiceps spp.

Prime Prime larvalfinal intermediate predilection

Adult host Larva host site

Multiceps dog Coenurus sheep central nervous (=Taenia) cerebralis system multiceps

Multiceps dog Coenurus rabbit connective (=Taenia) serialis tissue serialis

T. saginata is the "beef tapeworm of humans" and is one of the largest cestodes, with an average length of 5-10 meters.

Cattle become infected when their feed, or pastures are contaminated with feces of humans infected with T. saginata.

Eggs swallowed by cattle hatch in the duodenum and the liberated onchospheres enter the lymphatics or blood vessels

of the hepatic portal system and are blood-borne to the muscles via the general

circulation. They develop to oval infective cysticerci in 60 to 75 days. After ingestion by man in

inadequately cooked beef, cysticerci attach and grow to

sexually mature tapeworms in about 3 months.

Taenia saginata life cycle

Two cyclophyllidian tapeworms parasitize the small intestine of man in the adult stage, Taenia saginata and Taenia solium. The larval stage (cysticerci) of these parasites occur in meat from cattle ("beef measles") and swine ("pork measles") respectively.

Taenia Cysticercosis

Gravid, actively crawling segments are detached from the strobilus in the

intestines of infected humans and these eggs containing segments are passed in the stool. Individual eggs are difficult to

find by fecal flotation procedures for this reason. The number of eggs

available for cattle infection may be great, since an infected person often expels 8 to 9 segments daily, each of

which contain 80,000 to 100,000 eggs. Eggs do not survive desiccation well,

but retain infectivity well in moist situations on pastures for 60- 70 days

at 2OC and 180 days at lOC.

T. saginata gravid segment

Note the contained onchosphere with six

(...hexacanth) hooks which will be released by the digestive process and migrate to muscles

(usually within 24 hours).

T. saginata egg

Cysticerci (formerly called Cxsticercus bois develop as small oval structures which are at first transparent but later white and opaque

from encapsulation. They measure 7-10 mm by 4-6 mm in diameter at 60 to 75 days. Note the

single scolex and transparent cysts for each cysticercus.

T. saginata free cysticerci

Sites of localization in order of decreasing importance are: heart,

masseter muscles, shoulder, tongue, and other skeletal muscles. A "measly

beef" carcass may contain many thousand cysticerci. Cysticerci are

thought to remain infective for about two years, after which they calcify.

Prenatal infection of calves with blood-borne onchospheres has been

documented and is not uncommon in high incidence areas. Criteria for

rejection of infected beef carcasses or acceptance with trimming has been

covered previously under "Disposition of Carcasses". Cysts are destroyed by

freezing at -15F for 15 consecutive days or heating to 140F.

T. saginata cysticerci in situ

Cysticerci in muscle.

T. saginata cysticerci in tongue

T. saginata in man is easily identified by the lack of both hooks and a rostellum. It is the only "unarmed" tapeworm that occur in man.

T. saginata scolex

Note the single lateral genital pore of Taenia spp opposed to the central genital pore of Diphyllobothrium latum segments. In the United States, 12,000 to 16,000 infected cattle were discovered by meat inspectors annually from 1959 through 1967. Many cases occur as "outbreaks" in the Southwestern US and most are traced to infected migratory farm workers.

Human T.saginata infections are far more prevalent in the US than T. solium.

T. saginata mature proglottid

Taenia solium - Life Cycle

The life history of Taenia solium is essentially similar to T. saginata except that cysticerci occur in swine. Man is infected by pork eaten in

a cured form (such as sausage) or inadequately cooked condition.

Fully developed worms measure up to 7 meters long. It can be distinguished from T.saginata by the presence of

an armed rostellum.Note the double crown of 22 to 32 rostellar hooks

T. solium scolex

Massive infections are usual in swine and cysticerci show little predilection for specific muscle sites. In light infections,

greater numbers are found in muscles of the upper limbs, abdomen, and diaphragm. Cysticercus cellulosae is sometimes

used to refer to the larval stage in "pork measles".

T. solium cysticercus in ventricular myocardium

Taenia solium is unique among taenoid cestodes in having the potential for internal autoinfection of humans harboring adult worms. In some regions infection with the larval stage is as common as

infection with the adult worm.

Surgical removal of cysticerous from human

Cysticercus infection with T. solium can occur by two methods:1. by food or water contaminated by human feces, or self infection by transfer of eggs from the anal region to the mouth, and

rarely, reverse peristalsis results in gravid proglottids being carried to the stomach of humans harboring the adult worm.

The eggs are induced to hatch, and thousands of onchospheres are disseminated via the circulation. Massive

infections and even death has been documented, particularly in immunosuppressed or weakened individuals. Adult worms

in the intestine of man generally cause no serious damage for either T. solium or T. saginata but may result in loss of weight and mild digestive disturbances. Praziquantel is used to treat

adult Taenia spp. in man. Yomesan and a number of older preparations were used with mixed success in the past. In

some underdeveloped countries such as Mexico and Kenya, cerebral cysticerci are a major cause of CNS symptoms and

death. T. solium has an apparent predilection for brain localization in humans, especially after massive autoinfection .

Coenurus cerebralis in situ in sheep brain

The larval stage of Mu1ticeps multiceps, designated Coenurus cerebralis, arrives in the central nervous system as a blood-borne oncosphere. The coenurus is slow growing, and reaches maturity in 7 or 8 months at which time it may measure up to 5 cm in diameter. Signs are due to pressure necrosis, and a number of clinical effects may be seen depending on the site of the coenurus. Locomotor disturbances are the most common and include continuous or intermittent incoordination, exaggerated gait and circling, a condition commonly referred to as “gid” or “sturdy” by sheep raisers. Othersigns may include blindness, head

pressing, anorexia, and depression. Eventually recumbency and death ensue. “Gid” must be differentiated from listeriosis or louping-ill.

Dogs become infected by ingestion of infected brain or spinal cord tissues. Each scolex may develop to a mature tapeworm in the intestinal tract in 3-4 weeks. Multiceps multiceps is found primarily in the Western U.S. and in

countries with large sheep populations.

Coenurus cerebralis in situ in sheep brain

The life history of this cestode is esentially similar to M. multiceps, except that the intermediate host is a rabbit and the coenurus is located in the subcutaneous tissues. It differs from Coenurus cerebralis by the arrangement of the scolices in a line radiateing from a central point (thus “serialis”), and also by its propensity for both extemal and intemal budding. The adults are found in dogs and related canidae. Little is known of the geographic distribution in the U.S., but it has been occasionally reported in the Southeast.

Multiceps serialis - Coenurus in situ - rabbit connectiove tissue

Another important genus of the “taeniid” cestodes is one of the smallest tapeworms (up to 6mm) and consists of a scolex and three or four segments.

Because of its small size, this tapeworm is difficult to find at necropsy. The scolex is similar to that of Taenia spp. With a double row of hooks on the

rostellum.

Echinococcus

There is one immature, one or two mature, and one gravid segment. There are two important species, E. granulosus and E. multilocularis.

Echinococcus

The eggs, about 30 by 38u, are indistinguishable from those of dog Taenias. From the feces of dogs, wolves, or foxes they gain access to their intermediate hosts through contaminated forage or water. In addition to the animals noted above, pigs, horses, rabbits, and many other herbivores are susceptible. Human infection usually results from too intimate association with dogs; children are especially liable to infection by allowing dogs to lick their faces with a tongue which, in view of tbe unclean habits of dogs, is an efficient means of transfer of tapeworm eggs. Eggs transferred by the hands from an infected dog’s fur may also lead to infection.

Echinococcus life cycle

The intermediate host for Echinococcus granulosus include most of the domestic

animals and man. The most important host is the sheep, in which the highest proportion of

the cysts are fertile. Cattle and swine also serve as intermediate hosts, but many of the

hydatid cysts in these animals are sterile. In the United States, moose and deer are not

infrequently infected.

The larval stage of Echinococcus is the hydatid, tbe most complex of tapeworm larval forms. Germinal epithelium

produce individual scolices, brood capsules or daughter cysts. In older cysts, there is a granular deposit consisting of liberated

brood capsules and free scolices called “hydatid sand”.

Echinococcus Hydatid Cyst

After ingestion of eggs, the oncosphere becomes blood-borne and is filtered out in small capillary beds in any organ including

the liver or lungs (the most frequent localization sites) or in other tissues such as the brain, bone marrow, or other organs.

Hydatid cysts in horse liver

Hydatid cysts in sheep lung

Echinococcus hydatid cysts in situ

Hydatid cysts grow very slowly. The young larvae becomes a hollow bladder, around which the host adds an enveloping, fibrous cyst wall. At the end of a month cysts measure only 1mm; in 5 months they are about 10 mm and their inner surface begins producing brood capsules. As the cyst grows larger, brood capsules differentiate further and daughter cysts may be produced. Hydatids may eventually reach orange size or larger. After 10 or 20 years, they may contain many quarts of fluid and thousands of scolices.

Echinococcus hydatid cysts of various sizes

Note the brood capsules budding off from the delicate germinal epithelium and the thick

connective tissue wall produced by the host.

Echinococcus hydatid cyst - histosection

When cysts are ingested by dogs, very heavy infections with hundreds or thousands of adult E. granulosus results and patency occurs at 4-6 weeks. Clinical signs are minimal even when large numbers of adults are present. Due to the relatively short life of domestic animals and the long periods required for hydatids to mature, Echinococcus is of little economic importance to the livestock industry and its main importance is a public health hazard to man. New Zealand and Iceland have successfully controlled human echinococcosis by requiring frequent vermifuges for dogs and proper disposal of offal from livestock. In the U.S., Echinococcus is of highest incidence in Basquesheepherders in western mountain areas. Incidence in Argentina is 2-4.6 per hundred thousand people and 8.3 per hundred thousand in Greece. The greatest danger of human hydatidosis is loss of respiratory function in lung infections, and anaphylaxis from rupture of a cyst due to hypersensitivity to cyst antigens. The latter is an important consideration during surgical excision of cysts.

E. granulosus egg

E. multilocularis is closely related to E. granulosus and occurs in subarctic regions of Canada, Alaska, Europe and Asia as a

parasite of wild and domestic canidae. It has been found as far south as the Dakotas and Illinois of the U.S. and there is

concern this species is extending its range into the U.S. and also in Europe and may soon exceed E. granulosus as a public

health problem. The basic intermediate host is the vole. Recent spread may be due to re-establishment of former numbers and

range of foxes, other canidae.

E. multilocularis - exogenous budding

E. multilocularis differs from E. granulosus by exogenous budding to the outside of the cyst (as diagrammed here) rather than the

endogenous budding of E. granulosus.

Due to exogenous budding E. multilocularis has a growth pattern much like that of a neoplasm. This species is highly

invasive and metastases from primary liver hydatids may occur in distant organs. Although most domestic and wild animals are refractory to this parasite, man may be infected. The species is a very severe zoonotic disease transmitted from dogs to people in the endemic area. It initiates a highly invasive process in the liver and other body organs which is exceptionally difficult to

treat, since there is no drug available that affects the cyst stage.

E. multilocularis - histosection of vole liver

Order Pseudophyllidea

Two species of pseudophyllidian tapeworms occur to a limited extent in dogs and cats in the

U.S., Diphyllobothrium latum and Spirometra mansonoides. Both are covered in a handout

entitled “Meat, Fish and Water-borne Diseases of Public health Significance.”

Several key characteristics may be used to identify and diagnose pseudophyllidian

tapeworms.

The scolex is very small and has two slit-like bothria (rather than four circular suckers) which

serve as hold fast organs.

D. latem - scolex

Segments are retained and not shed continuously by pseudophyllidian tapeworms. Proglottids are of nearly uniform size and maturity and passage of individual

operculated eggs rather than segments are the means of egg dispersal. Genital structures and the genital pore are

located centrally on each segment (as seen here) and may be seen grossly.

D. latum - segment

Diphyllobothrium latum is a pseudophyllidian tapeworm which is commonly known as the "broad fish tapeworm " of man and other fish-eating mammals such as dogs, cats, bears, etc. The life cycle involves two intermediate hosts, small fresh water crustaceans known as "copepods" and various fresh water fish.Operculate eggs hatch outside the final hosts' body in water in about 2 weeks, liberating the first larval stage, a free-swimming, ciliated coracidium. After ingestion by certain copepods (i.e. Cyclops) the coracidium develops in another two weeks to the procercoid stage. When the copepod is eaten by fish, the second intermediate host, the procercoid migrates to the muscles and other organs and develops to the plerocercoid stage. The plerocercoid is about 5mm long and is visible in exposed muscle of infected fresh-water fish, including pike, perch, trout, salmon and others. If small fish infected with plerocercoids are ingested by larger fish, the larval tapeworms, having paratenic tendencies, migrate to the muscles and viscera of the new host and re-encyst, a process that can be repeated in a long series of fish hosts. Man and other hosts are infected by ingestion of the plerocercoid in uncooked, pickled or "cured" fish.

Diphyllobothrium latum life cycle

The egg is oval, yellowish and operculated, and is somewhat similar to Fasciola hepatica in appearance but is much smaller (70u by 45u). A posterior "knob" is sometimes visible opposite the operculated end (as

seen here).

Diphyllobothrium egg


seen here).


The coracidium is an apparent biologic analogy to the trematode miracidium, but consists of a hexacanth onchosphere with a ciliated coat.

D. latum coracidium emerging from egg


seen here).


Like miracidia, the coracidium requires a water environment and must be ingested by a copepod

intermediate host within 24 hours or it dies.

Cyclops- lst intermediate host


seen here).


D. latum attaches to the mucosa of the small intestine and is the longest known cestode, reaching a length of 15 meters and consisting of more than 4000 segments. It is a very fast-growing cestode and can reach a length of a meter in three weeks. The first eggs appearing in the feces in about four weeks after ingestion of pleurocercoids and the worm may survive ten years or more. As a rule eggs can be found in the feces of the definitive host, in contrast to infection with

Adult Diphyllobothrium latum

cyclophyllidian tapeworms in which eggs are released in gravid segments passed from the body . D. latum segments are shed only when they are old and no longer capable of producing eggs. The majority of segments are in the same stage of development and are more uniform in size than cyclophyllidian tapeworms.


seen here).


D. latum is easily recognized by its large

size, central genital pore in square segments

and long unarmed scolex with two

elongate, groove-like suckers called

bothria.

Genital pores are lateral in cyclphyllidian tapeworms.


seen here).






bothria.


Diphyllobothrium latum is unusual among cestodes in being pathogenic in the adult stage. The capacity of D.latum for

depriving its human host of vitamin B12 to produce pernicious anemia (macrocytic, hyperchromic) is well documented. It

does this by two mechanisms: (1) it interferes with absorption of B12 by blocking the combination of B12 and an intrinsic factor

from the gastric mucosa and (2) it absorbs and binds large amounts of B12 in its own tissues. D. latum contains 15 times as much B12 as other cestodes and a powdered preparation of its segments may actually be used to treat victims of an active

infection.

Infection rates are highest in cultural groups which traditionally eat roe or fresh water fish raw, lightly salted, or pickled without

cooking. Incidence is highest in the US in people of Scandinavian extraction in the Great Lakes region. Eskimos in Alaska and Jewish people fond of gefilte fish (spiced minced

fish) are also prone to infection. Plerocercoids are killed in fish subjected to freezing at -l0°C for 24-48 hours or cooking at

over 56 °C for 5 minutes.


seen here).






bothria.






infection.





Although dogs, cats, and other mammals may be infected the importance of wild and domestic

animals as reservoirs is unknown and man is thought to be the main host for D. latum. There are differing opinions on the capacity of eggs

produced in animals to hatch and infect copepods. Quinicrine (®Atabrine) and niclosamide (®Yomesan) are effective

treatments in man. Dogs may be successfully treated with arecoline preparations (®Nemural)

and cats may be treated with kamala. Praziquantel at 3 times label dose is the

treatment of choice for dogs, cats and man.

Diphyllobothrium Treatment


seen here).






bothria.






infection.





Spirometra spp. are pseudophyllidian tapeworms that occur in the adult stage in the intestine of cats, dogs and certain wild carnivores. The life cycle is similar to Diphyllobothrium. Unlike D.

latum, it is the opportunistic plerocercoid stage which is of importance as a public health

problem, not the adult stage. The plerocercoid larvae of worms of the genus Spirometra were designated as Sparganum spp. before the adult

forms and life cycle became known. "Sparganosis" is still used to refer to infection by

plerocercoids of Spirometra.

Spirometra (sparganosis)


seen here).






bothria.






infection.





Spirometra spp. are pseudophyllidian tapeworms that occur in the adult stage in the intestine of cats, dogs and certain wild carnivores. The life cycle is similar to Diphyllobothrium. Unlike D.

latum, it is the opportunistic plerocercoid stage which is of importance as a public health

problem, not the adult stage. The plerocercoid larvae of worms of the genus Spirometra were designated as Sparganum spp. before the adult

forms and life cycle became known. "Sparganosis" is still used to refer to infection by

plerocercoids of Spirometra.

Spirometra (sparganosis)

As with D. latus, eggs laid in water hatch to coracidia, are ingested by fresh water copepods, in which development to the procercoid stage occurs. When infected copepods are swallowed by mice, water snakes or amphibians (depending on the species of Spirometra) the plerocercoid stage develops. Cats or dogs may become infected by ingesting infective plerocercoids and begin passing operculated eggs in about 2 weeks. Spirometra mansonoides has a wide distribution in wild and feral cats in the Eastern USA and uses wild species of mice for the plerocercoid (spargana) stage. Man on rare occasion enters this life cycle as an accidental host, as can a wide variety of other warm or cold blooded animals. While procercoids and adult Spirometra are restrictive in the copepods or definitive host(s) they can develop in, the plerocercoids have the capacity to develop in almost any animals and almost indefinite serial plerocercoid transmission may occur (frog, mouse --- snake --pig --- man, etc.). Man and other animals therefore act as paratenic hosts for plerocercoids (spargana) in which the parasite is unable to develop beyond this stage to sexual maturity . Plerocercoids of Spirometra mansonoides enter the human gut migrate to body tissues and appear as spargana. Animals incriminated in transmission to man include poorly cooked tissues of domestic and feral pigs, chickens and other fowl, frogs and snakes. An alternate mode of infection for some Spirometra spp. is by ingestion of infected copepods in water in which case development to migrating plerocercoids occurs. In Asia, infections occur by migration of spargana from raw flesh of frogs which are applied to wounds as poultices by local inhabitants.

Spirometra Life Cycle

In this species which occurs in the Eastern USA,

"spargana" are found in SQ tissues and musculature of

mice.

Spirometra mansonoides plerocercoid

The scolex occurs in the blunt, thicker

anterior end.

Dracunculus medinensis (guinea worm, fiery serpents). This nematode has been known since

ancient times and is referred to in the Bible as the "fiery serpents" afflicting the Israelites by the Red

Sea. They occur as very long (2-4 feet) worms coiled in the subcutaneous tissues, especially on the

extremities. Toxic materials are excreted which cause a blister which ulcerates. Under the stimulus

of contact with water, female worms eject milky fluid, containing myriads of larvae from the uterus

into the water. If ingested by copepods, larva develop to infective larvae which may then infect a new host by ingestion in drinking water. A similar species, Dracunculus insignia occurs in raccoons

and occasionally dogs in the USA.

Dracunculus medinensis

Another nematode which occurs in marine fish is Anasakis marina. This parasite causes severe eosinophilic granulomas or ulceration in the

gastrointestinal tract of man following accidental ingestion of encapsulated larvae (2 cm long) in the viscera and flesh of raw, salted or pickled herring, cod, mackeral and other fish. Marine

mammals, (dolphins, porposes, seals) are thought to serve as the normal definitive host for the adult stage of Anasakis. Larvae are killed by

deep freezing (-2OC for 24 hours). Infections occur mainly in Japan and the Netherlands who

customarily eat raw marine fish.

Anasakis

Two cyclophyllidian tapeworms parasitize the small intestine of man in the adult stage, Taenia saginata and Taenia solium. The larval stage (cysticerci) of these parasites occur in meat from cattle ("beef measles") and swine ("pork measles") respectively.

Taenia Cysticercosis

Individual eggs develop in water to produce a ciliated coracidia. Eggs of Diphylobothrium and Spirometra are very similar in size

and appearance and are easily overlooked in routine fecals because they approximate the size of a hookworm egg (see Sloss p. 68). Eggs of both species float with NaNO3 solution.

Diphyllobothrium latum is not thought to occur in dogs and cats in the Southeast, but Spirometra mansonoides is widespread in

wild animals in the eastern U. S ., including the Gulf Coast States.

Pseudophylidian operculated egg

The life cycle of Spirometra mansonoides is similar to that of D. latum, except for the second intermediate

host. Plerocercoids develop primarily in mice and snakes rather than fish. Infections occur in cats (to a lesser extent in dogs) by ingesting infected tissues. The bobcat is thought to be the primary definitive

host. Adult Spirometra are relatively small in comparison to D. latum and they seldom exceed 1

meter in length.

Mesocestoides is a seldom reported tapeworm of dogs and other carnivores (Williams et al (1975), JAVMA 166, 997). The classification, life cycle and transmission of Mesocestoides is controversial but these tapeworms seem to occupy a position interposed between the cyclophyllidean and pseudophyllidean

tapeworms. Two intermediate hosts are thought to be required, an arthropod (possibly orbatid mites) and a

vertebrate (birds, small rodents, reptiles). Unique larval forms occupy the serous cavities and when ingested by the final

host, develop to maturity in about 3 weeks.

The clinical features of the infections and gross appearance of shed proglottids may lead to diagnositic confusion with

Dipylidium. Eggs are seldom shed; squash preparations of segments reveal individual thin shelled eggs containing a

hexacanth embryo (see Sloss). The genital opening is centrally (not laterally) placed on segments and the scolex of adults has

four suckers but no hooks.

Mesocestoides spp.

Despite their dramatic impact on clients and their frequently large size, adult tapeworms in general cause very little harm in dogs and cats and their importance is often exaggerated. Competition with the host for nutrients by tapeworms (by direct absorption through the tegument) occurs, but is serious only with Diphyllobothrium latum (B12 deficiency results). Usually, the signs due to the common tapeworms consists only of vague gastrointestinal upsets, perhaps with diarrhea and emaciation due to mild enteritis with heavy infections. Gravid segments of cyclophyllidean tapeworms may migrate through the anal sphincter onto the perineum causing pruritis. Affected animals assume a sitting position and scoot on the ground to relieve irritation. (A far more common cause of scooting, however, is impacted anal glands). Rarely, segments may cause impaction by lodging in the anal glands.

It is important to identitfy tapeworms to species or atleast genus level to be able to identify the probable source of infection and to make sound recommendations on control measures. This can be done by identifying eggs in fecal flotation of squash preparations, by finding proglottids or “rice granules” on the perineum, or by identification of whole worms passed after treatment. The latter is best done by placing segments in water in the refrigerator overnigth to “relax” proglottids (or “unwrap” rice granules) to allow them to assume typical shape.

Clinical Signs and Diagnosis

Treatment and Control of Common Cestodes Qf Dogs and Cat

For many years the only treatment available for cestodes were old-time drug preparations of vegetable origin (Kamala, Kousso, felix mas, arecoline hydrobromide), organic heavy metal preparations, (Nemura1; Anthelin) or combinations of these drugs. These drugs act by purgation (parasympathomimetic), have little or no efficiency against other helminths, have low safety margins, and often result in only shearing the strobila off, leaving the scolex to regenerate. Two commercial products, Yomeson (no longer available) and Scolaban act on the scolex with a high safety margin in dogs and cats. Praziquantil (Droncit) and Epsiprantel (Cestex) are the most effective and widely used cesticide in current use. Tapeworms are killed and digested after treatment and are therefore not often found in the stool (unlike the more dramatic passage of tapeworms with vermifuges).

The following may be used in dogs for Taenia spp. and or Dipylidium. A repeat treatment should be given in 2-4 weeks.

1. Di-phenthane- 70- (in ® Vermiplex) "Aid in Removal Only"2. Di-phenthane - 70 plus arecoline hydrobromide 3. ®Nemura1 (brand of Drocarbil-Winthrop Labs;an organic arsenical combined with arecholine = “vermifuges”4. ® Anthelin (an organic antimonial with arecholine)5. ® Yomesan (Niclosamide) - Removed from market6. ® Scolaban (Bunamidine HCL) – Removed from market7. Fenbendazole (®Pancur), febantel (® Rintal) Affects taeniid tapeworms only.8. ® Droncit (praziquantel) - Cyclophyllidian & Pseudophyllidian; current drug of choice for human schistosomiasis - (®Drontal is pyrantel + praziquantel ± febantel) 9. ®Cestex (Epsiprantel) - Enteric tapeworms only

Checklist: Tapeworms of Domesticated Animals

Adult Definitive Larval Intermediate Larval

Parasite Host Stage Host Predilection

SiteTaenia hydatigena Dog Cysticercus tenuicolli Sheep, Cattle, Pig Peritoneum

Taenia pisiformis Dog Cysticercus pisiformis Rabbit Peritoneum

Taenia ovis Dog Cysticercus ovis Sheep Muscle

Multiceps multiceps Dog Coenurus cerebralis Sheep C.N.S.

Multiceps seralis Dog Coenurus seralis Rabbit Connective

tissue

Taenia taeniaformis Cat Cysticercus fasciolaris Mouse, Rat Liver

Echinococcus granulosus Dog, Cat, Hydatid cyst Cattle, Sheep, Pig Liver, Lungs

Canids

(Continued on Next Slide)



SiteDipylidium caninum Dog, Cat, Fox Cysticercoid Flea ( dog or cat) Body Cavity

Mesocestoides spp. Dog, Cta, Canids Cysterceroid 1 st: Mite Peritoneum and 2nd: Mammals , Pleura

Birds, Reptiles

Spirometra spp. Dog, Cat, Canids Procercoid 1 st: Cyclops Body Cavity

Plerocercoid 2 nd: Mammals and SubQ

Amphibians, Reptiles

Diphyllobothrium latum Man, Dog, Cat, Procercoid 1 st: Cyclops Body Cavity

Pig Plerocercoid 2 nd: Fresh water fish Muscle

Moniezia expansa Sheep, Cattle, Goats Cysticercoid Orbatid mites Body cavity

Moniezia expansa Sheep, Cattle Cysticercoid Orbatid mite Body cavity

Thysanosoma actinioides Sheep, Goats, Cysticercoid Orbatid mite Body cavity

Cattle

( CONTINUED ON NEXT SLIDE)



Site

Anoplocephala perfoliata Horses Cysticercoid Orbatid Mite Body Cavity

Anoplocephala magna Horses Cysticercoid Orbatid Mite Body Cavity

Paranaplocephala mamillana Horses Cysticercoid Orbatid Mite Body Cavity

Taenia saginata Man Cysticercus bovis Cattle Muscle

Taenia solium Man Cysticercus cellulosae Swine Muscle

Hymenolepis spp. Rat, Man, Mouse Cysticercoid Grain Beetles Body Cavity

tapeworms of dogs and cats. "tapeworms" are members of the class cestoda which are...

Documents

mature tapeworms

tapeworms of dogs

cats tapeworms

pseudophylidean tapeworms

scolex of dipylidium

caninum specimens

caninum scolexd

final host