Veterinary Parasitology Lecture PDF

Veterinary Parasitology Helminthology and Immune Parasitology Code: PAR314 Dr. Mohamed Abdelmoghny [email protected] / [email protected] https://linktr.ee/dr_vet98  Phylum: Platyhelminthes...

Veterinary Parasitology Helminthology and Immune Parasitology Code: PAR314 Dr. Mohamed Abdelmoghny [email protected] / [email protected] https://linktr.ee/dr_vet98  Phylum: Platyhelminthes Class: Cestoda (Tape worms) General Characteristic features: 1. They are elongate, ribbon-like worms, flattened dorsoventrally with neither body cavity nor alimentary canal. 2. They are endoparasites, found in small intestine of vertebrate definitive host except Anoplocephala (in large intestine of equines), Stilesia hepatica and Thysanosoma actinoides found in bile ducts of sheep and cattle. 3. The body is segmented (divided into segments or proglottid) with variable size from few millimetres to several meters. 4. Hermaphroditic worms; each mature segment, containing one and sometimes two sets of male and female reproductive organs. 5. Life cycle is mostly indirect, the larval worms (metacestodes) inhabit the tissues of vertebrates and invertebrates intermediate hosts. 6. This class includes two orders of medical and veterinary importance: a) Order Eucestoda (Cyclophyllidea); true tapeworms have a scolex with four suckers, non operculated egg. b) Order Cotyloda (Pseudophyllidea); pseudo-tapeworms have a scolex with two longitudinal slits, operculated egg. Veterinary Helminthology 107 General Morphology: Class: Cestoda (Tape worms) External Structure: 1. Size: Length differs from 3 mm (Davainea proglottina) to over 20 meters (Taenia spp.). 2. Colour: White creamy or yellowish adult tapeworms. 3. The body: The adult cestode consists of a head or scolex bearing attachment organs, a short unsegmented neck and a chain of segments. The chain is known as a strobila and each segment as a proglottid. Number of segments differs from 3 (Echinococcus) to 4000 segment (Taenia spp.). a) Scolex: globular or pyriform structure equipped for attachment to the intestinal wall of the host by mean of; Suckers: cup- like muscular sucking disks on the sides of the scolex (Taenia saginata). Rostellum or proboscis: a mobile protrusible cone armed with chitinous hooks (Taenia solium). Bothria: elongated suctorial groove or slit with a shallow depression(Diphyllobothrium latum). Pseudoscolex: a distortion of the anterior part of the strobila to form the hold fast organ in early developmental stages of cestodes. Hooks: An arming structure of rostellum, each consists of a blade (B), handle (H) and guard (G); Taenoid hooks (B=H), Hymenolepis hooks (H is very long), Rose-thorne hooks (B in the middle, H=G) as in Dipylidium and Hammer shaped hooks (B=H, guard is long) as in Davainea and Railietina. Veterinary Helminthology 108 General Morphology: Class: Cestoda (Tape worms) External Structure: B) Neck: The short unsegmented part, just behind the scolex. C) Strobila: The segments or proglottids which are continuously budded from the posterior neck region. ▪ They begin by undifferentiated immature segments gradually merge into large mature segments with 1 or 2 sets of completely formed sexual organs of both sexes and these in turn merge into gravid proglottids which consist essentially of a uterus distended with ova. ▪ The proglottids vary greatly in number, size and shape according to the species and the stage of development. The shape and internal structure of the proglottid is useful for species differentiation. ▪ They may be longer than they are broad, broader than long or square. ▪ The small Echioncccus granulosus has one immature, one mature and one gravid proglottids. In contrast, thousands of proglottids found in the large Taenia saginata. ▪ In Eucestodes, The gravid segments are usually shed intact from the strobila and pass out with the faeces. Outside the body, the eggs are liberated by disintegration of the segment or are shed through the genital pore. ▪ In Pseudocestodes, they have a uterine pore through which the ova are liberated form the ripe proglottids as the uterus does not have lateral branches distended with ova and the ripe segments are not shed of as in the true tapeworms. Veterinary Helminthology 109 General Morphology: Class: Cestoda (Tape worms) Internal Structure: 1. Excretory System: It is composed of flame cells distributed throughout the parenchyma leading to efferent canals (ventral longitudinal Canals), which extending along each of the lateral margins of the segments, unite at the posterior part of each segment by transverse duct and run through the strobila to discharge at the terminal segment. 2. Nervous system: Composed of two cephalic ganglia found in the scolex, one in each side and connected by a nerve ring from which six longitudinal, two dorsal and two ventral nerve cords run posteriorly. 3. Reproductive system: The Cestodes are hermaphroditic, each mature proglottid contains a one or two complete set of male and female reproductive organs. In Eucestoda, the genital pores usually opening on the lateral margin of the segments; unilateral or on the same side (Hymenolepes) or irregularly alternate (Taenia) or both margins of the segment when two sets of reproductive organs are present (Dipylidium). In Pseudocestoda, the male and the female genital pores have common opening on the ventral surface of the proglottid. Veterinary Helminthology 110 General Morphology: Internal Structure: Class: Cestoda (Tape worms) a) Male genital system is formed of a number of testes which differs from 3 (Hymenolepis) -500 or more (Taenia) situated in the dorsal part of the proglottid. Vasa efferentia arise from testes and join to form vas deferens leading to seminal vesicle followed by cirrus and cirrus pouch which open anterior to the vagina in the common genital atrium. b) Female genital system consists of bilobed ovary situated in the posterior part of the proglottid, ootype surrounded by Mehli’s gland, vitelline glands and uterus which has a characteristic shape in different genera (lobulate transverse sac (Hymenolepis), in a reticulate pattern (Moniezia), or extensively branched (Taenia)). The uterus arises up ending blindly (Eucestodes) or in uterine aperture (Pseudocestodes) while the vagina opens in the female genital pore. The vitelline glands either compact or diffused or absent in some genera and located in the lateral bands or at the posterior margin or spread over the segment. The fertilization takes place in the ootype. ▪ Both self-fertilisation and cross-fertilisation between proglottids of the same or other worms may occur. Veterinary Helminthology 111  General Life cycle and Developmental stages of Cestodes ▪ The cestode life cycle is indirect and needs one (Eucestodes) or two intermediate hosts (Psudocestodes). In case of Hymenolepis nana, direct type of life cycle is also reported. ▪ Eggs: - In Eucestodes, the intact gravid segments are detached either singly or in chain and non-operculated embryonated eggs liberated by disintegration of the segment (Apolysis). These eggs contain mature hexacanth embryo (onchosphere, having 6 hooks) covered by embryophore, a thick and radially striated envelop. Once ingested by intermediate host, oncospheres penetrate the intestinal wall with the help of their hooks and develop into metacestodes (larval stages of cestodes) in the body cavity (invertebrates) or different body parts (vertebrates). - In Pseudocestodes, the eggs are shed through the uterine pore from the ventral surface of mature segments. The eggs are light brown, operculated and contain immature embryo which need a certain period for maturation and then hatch in fresh water giving coracidium (onchosphere covering by ciliated embryophore, motile in nature). The metacestodes develop in the two intermediate hosts involved in the life cycle. Veterinary Helminthology 112  General Life cycle and Developmental stages of Cestodes ▪ Metacestodes (larval stages of cestodes): In Eucestodes (cystic larvae): 1. Cysticercoid: It’s a small solid cyst with double cyst-walled structure having single evaginated scolex. It’s the larval stage of non-taeniid eucestodes like Moneizia and Dipylidium and developed in the body cavity of the invertebrate intermediate host like oribatid mites and fleas. Cysticercoid may be either: Cercocystic cysticercoid with a tail-like appendage or Cryptocystic cysticercoid without tail. 2. Cysticercus: It’s a large fluid filled bladder-like cyst with single wall enclosing single invaginated scolex (Protoscolex). It is formed mostly between the muscles of the vertebrate intermediate host in taeniid worms. It differs in size according to species. Examples: Cysticercus cellulosae , C. bovis, C. taenuicollis, C. ovis, C. pisiformis. 3. Coenurus: It’s similar to cysticercus but is larger and having numerous invaginated scolices with very delicate membraneous wall. It is formed in different tissues of vertebrate intermediate host; Coenurus cerebralis in C.N.S. or Coenurus serialis in the subcutaneous tissues. 4. Strobilocercus: It’s a worm-like cyst with single evaginated scolex having along segmented strobila without sexual proglottids as Cysticercus fasciolaris, the larval stage of T. taeniaeformis developed in rodents. Veterinary Helminthology 113  General Life cycle and Developmental stages of Cestodes ▪ Metacestodes (larval stages of cestodes): In Eucestodes (cystic larvae): 5. Hydatid cyst: This is a large fluid-filled cyst lined with germinal epithelium from which are produced invaginated scolices which lie free or in bunches, surrounded by germinal epithelium (brood capsules). The contents of the cysts other than the fluid, i.e. scolices and brood capsules, are frequently described as ‘hydatid sand’. Daughter cysts are formed endogenously or, if the cyst wall ruptures, exogenously (unilocular or multilocular). It’s formed in the internal organs of vertebrate (Liver & lung) intermediate hosts as in Echinococcus granulosus. In Pseudocestodes (Solid larvae): 1. Procercoid: It’s developed from coracidium in the body cavity of the first intermediate host (Cyclop). It is sloid elongated body with a cephalic invagination and a posterior spherical appendage (Cercomer) with the embryonal hooklets. It is about 0.5 mm in length. 2. Plerocercoid: It is formed in the muscle or liver of the fish (second intermediate host). About 1.5-2 cm in length, elongated solid bodies, worm-like with superficial annulations bears the future adult scolex (almond shaped bothria). Some plerocercoids may develop the genitalia. ▪ When the metacestode is ingested by the final host the scolex attaches to the mucosa, the remainder of the structure is digested off, and a chain of proglottids begins to grow from the base of the scolex. Veterinary Helminthology 114  Difference between the two orders of Cestodes Character Cotyloda (Pseudophyllidea) Eucestoda (Cyclophyllidea) Scolex Almond or spoon-shaped with a slit like grooves Globular bear 4 Suckers and rostellum with or (bothria) without hooks Strobila Genital pore found on ventral surface Genital pore found on lateral surface (marginal) Vitelline gland is diffuse small follicles Vitelline gland is compact mass posterior to ovary Uterus is coiled with uterine pore Uterus is blind sac Method of egg via uterine pore by apolysis (detachment and disintegration of dissemination (No gravid segment) gravid segment) Diagnostic stage Ova only (operculated, unembryonated) Ova and proglottids (Non-operculated and embryonated) Embryo coracidium or ciliated larva oncosphere, hexacanth embryo (free swimming) (non–ciliated) Hatching occurs in water occurs after ingestion by intermediate host Intermediate host two (Cyclops & fish) one Type of larval stage solid bladder or cystic Veterinary Helminthology 115  Classification of Cestodes Order Pseudophyllidea (Cotyloda) Family Diphyllobothriidae The genus Diphyllobothrium is an important cestode of humans and fish- eating mammals. They are long tapeworms with an unarmed scolex, with two muscular bothria. The genus Spirometra are tapeworms of dogs, cats and wild carnivores and an occasional human zoonosis (sparganosis). Order Cyclophyllidea (Eucestoda) Family Taeniidae The adults are found in domestic carnivores and man. The scolex has an armed rostellum with a concentric double row of hooks (the important exception is Taenia saginata whose scolex is unarmed). The gravid segments are longer than they are wide. Genera of importance are Taenia (syn Multiceps) and Echinococcus. Family Anoplocephalidae These are essentially tapeworms of horses (Anoplocephala, Paranoplocephala) and ruminants (Moniezia). The scolex has neither rostellum nor hooks and the gravid segments are wider than they are long. Veterinary Helminthology 116  Classification of Cestodes Order Cyclophyllidea (Eucestoda) Family Dilepididae Family Thysanosomidae These are tapeworms of the dog, cat (Dipylidium), and the fowl Closely related to the Anoplocephalidae, this family (Amoebotaenia, Choanotaenia, Metroliasthes). The scolex contains several tapeworms of veterinary importance usually has an armed rostellum with several rows of hooks. The found mainly in sheep and other ruminants (Stilesia, intermediate stage is a cysticercoid. Thysanosoma, Thysaniezia and Avitellina). The intermediate stage is a cysticercoid present in forage Family Davaineidae mites of the family Oribatidae. These are mainly parasites of birds (Davainea, Raillietina, Cotugnia). These tapeworms usually have rows of hooks on both Family Mesocestoididae rostellum and suckers. The intermediate stage is a cysticercoid. Also of minor veterinary importance, these cestodes of carnivorous animals and birds have two metacestode Family Hymenolepididae stages. The first is a cysticercoid in an insect or mite, and These parasites are of minor veterinary importance. Members of this the second a solid larval form, a tetrathyridium, in a family, which have a characteristically slender strobila, infect birds, vertebrate. Genera include Mesocestoides found in dogs, man and rodents (Hymenolepis, Rodentolepis, Fimbriaria). The cats and wild mammals, and Dithyridium in chickens, intermediate stage is a cysticercoid present in an arthropod host. turkeys and wild birds. Veterinary Helminthology 117 Order Pseudophyllidea (Cotyloda) Family: Diphyllobothriidae ▪ Medium sized to large tapeworms. Genus: Diphyllobothrium ▪ Scolex has two groove-like bothria used for attachment. ▪ One set of reproductive organs in each proglottid. D. latum ▪ The ovary is bilobed and uterus is rosette shaped or spiral tube. Genus: Spirometra ▪ No gravid segments. ▪ The egg pass through a uterine pore situated on the ventral S. mansoni surface of the segments. They are operculated and unembryonated (contain immature embryo) like trematodes. ▪ Testes are scattered over the segments and the vitelline glands are distributed in the lateral fields of the segments. ▪ The onchosphere is ciliated, called coracidium and two intermediate hosts are needed for completing their life cycle. ▪ Larval stages are solid; procercoid (occurring in 1st I.H “copepods crustacean”) and plerocercoid (found in 2nd I.H host “ fish” ). Veterinary Helminthology 118 Genus: Diphyllobothrium D. latum Broad tapeworm ▪ Synonym: Dibothriocephalus latus. ▪ Common name: Broad tapeworm or bread-fish tapeworm. ▪ Final host: Man and fish-eating mammals, such as the dog, cat, pig and polar bear. ▪ Intermediate host: 1st I/H; Copepods crustacean (Cyclops). 2nd I/H; Freshwater fish (Salmon, trout, perch and pike). ▪ Habitat: Small intestine ▪ Disease/Pathological condition caused: Diphyllobothriasis or fish tapeworm infection. ▪ Geographical distribution: Parts of Scandinavia, Russia, Japan and North America. ▪ Morphology: Gross: A very long, yellowish grey tapeworm, up to 20 m in length, with several hundred proglottids and dark central markings caused by the rosette shaped uterus and eggs. The scolex is unarmed with two muscular longitudinal grooves or bothria; one dorsal and another ventral as organs of attachment. Microscopic: Mature segment is broader than long has bilobed ovary, diffuse testes mixed with vitelline glands in lateral side of the proglottid. Uterus is convoluted, rosette-shaped and centrally-located, open ventrally in the uterine pore which lying immediately posterior to the genital pore. Veterinary Helminthology 119 Genus: Diphyllobothrium D. latum Broad tapeworm ▪ Diagnostic stage: unembryonated Eggs in Faeces. Eggs are ovoid in shape, 70 x 50 µm, light brown, operculated, have rounded ends and contain immature embryo. It passed continuously into the faces of the host and take several weeks to be embryonated. ▪ Metacestodes: ▪ Procercoid: First larval stage of D. latum, solid larva. Elongated, 0.5 mm long, with a cephalic invagination and circular appendage containing the sex embryonal hoklets. ▪ Plerocercoid: The second larval stage of D. latum, solid larva, 1.5- 2 cm X 2-3 mm in size. Elongated in shape with evaginated anterior end which is followed by pseudo-segmented body. ▪ Infective stage: Plerocercoid in the liver or muscles of the fish. ▪ Mode of infection: Ingestion of infected fish or caviar containing the plerocercoid of D. latum. The plerocercoid can be clanged to the hands of fish cleaners and accidentally introduced into mouth. Veterinary Helminthology 120 Life cycle: ▪ Life cycle: Indirect (two intermediate hosts is required). ▪ Developmental stages: Eggs are continuously discharged from the genital pores of the attached segments of the strobila and pass to the exterior in the faeces. Eggs develop in fresh water after 2-3 weeks and the coracidia hatch and swim in water by their cilia. The coracidium is engulfed by water flea (Cyclops 1st intermediate host), in which the coracidium develops into procercoid in its body cavity. When the infected cyclop is ingested by a freshwater fish, salmon, the procercoid migrates to the muscles or viscera to form the second larval stage, the plerocercoid. The final host is infected by eating raw or imperfectly cocked or insufficiently salted fish. The adults are developed in the small intestine occurring within 3-4 weeks of ingestion of the plerocercoid. ▪ Prepatent period: 3-4 weeks. Pathogenesis and clinical signs: ▪ In man, infections are often asymptomatic but there can be fatigue, abdominal pain, vomiting and transient diarrhoea. Infection is usually asymptomatic in animals although occasionally vitamin B12 deficiency can occur. ▪ A pernicious anaemia may develop due to absorption of unsaturated fatty acid liberated by the worm and tendency of the worm to pick up vitamin B12. Intestinal obstruction may occur. Veterinary Helminthology 121 Epidemiology: ▪ D. latum is a parasite of man since in other hosts the cestode produces few fertile eggs. ▪ The epidemiology is therefore largely centred around two factors, the access of human sewage to freshwater lakes and the ingestion of uncooked fish. ▪ Domestic animals, such as dogs or pigs, become infected by eating raw fish or fish offal. Diagnosis: 1. Clinical symptoms (non-specific). 2. The detection of the characteristic eggs in the faeces (differential diagnosis from Fasciola eggs which are larger and without posterior knob). Egg 70 X 50 μm in size, Ovoid, yellowish brown, thin-shelled and contains one cell stage embryo surrounded by yolk cells with an inconspicuous operculum and a small knob-like thickening at the other pole. Treatment: ▪ Praziquantel (5-10 mg/kg) and niclosamide are effective against the adult tapeworm. Control: ▪ Eradication of the first intermediate host in endemic areas by filtration and boiling of water. ▪ In areas where infection is common, domestic animals should not be fed fish products unless these have been thoroughly cooked or deep-frozen. ▪ Perfect cooking and pickling of fish for human consumption with proper disposal of sewage. Veterinary Helminthology 122  Genus: Spirometra S. mansoni ▪ Synonym: Diphyllobothrium mansoni / Sparganum mansoni. ▪ Final host: Dogs, cat, wild carnivores and occasionally man. ▪ Intermediate host: 1st I/H; Copepods crustacean (Cyclops). 2nd I/H; Amphibia, reptiles, birds and mammals. ▪ Habitat: Small intestine ▪ Disease/Pathological condition caused: Human Sparganosis (No disease in D/H but in 2nd I/H). ▪ Geographical distribution: South America and Asia. ▪ Morphology: The morphology and life cycle of these tapeworms is similar to that of D. latum, only differentiating characters are smaller (60-120 cm), convoluted spiral uterus (2-6 coils), uterine pore & vagina open separately on the ventral surface of the proglottid. ▪ Life cycle: The life cycle are similar to that of D. latum except the second intermediate host and PPP= 10-30 days. ▪ Diagnostic stage: Eggs are operculated unembryonated pointed, rather than rounded at each end. ▪ Metacestodes: The procercoids being found in crustaceans, such as Cyclops, and the plerocercoids (Sparganum, Sparagna) develops in frogs, snakes, birds and mammals including man, white ribbon- like structures may reach several centimetres in length (10–20 cm) occur in muscles and subcutaneous tissues especially around the eye. ▪ Pathogenesis and pathology: The tapeworm usually causes little effect in the intestine of dogs and cats. ▪ Clinical signs: Usually asymptomatic in animals. Veterinary Helminthology 123  Human Sparganosis ▪ Definition: Infestation of the human tissue by the larval stages of Diphyllobothrium (= Spirometra) mansoni which is called Sparganum. It is identical with Plerocercoid but it is up to 10-20 cm long. ▪ Methods of infection: 1. Eating of insufficiently cooked or salted fish, pigs, frogs and reptiles infected with plerocercoid (sparganum) stage, which migrate inside the body of man and can settle in any organ (cannot develop into adult worm). 2. Accidental ingestion of infected Cyclops with drinking water containing procercoid which penetrates the intestinal wall and migrates to subcutaneous tissues or any vital organs and develops into sparganum. 3. Applying the infected flesh of frogs, snakes and birds (paratenic hosts) which contain the sparganum stage to the ulcerated parts of the body (wounds) or the eyes. Sparganum directly migrates to human tissue and can settle in the skin or eye causing cutaneous or ocular sparganosis respectively. ▪ Pathogenesis: It is characterised by the presence of larvae up to 35 mm long in the muscles and subcutaneous tissues, particularly the periorbital area, in form of irregular nodules (1-2 cm), persist for months or even years. The ocular sparganum produces severe pain, irritation, swelling of the eye-lids with excess lacrimation. Inflammation and oedema according to the organ invaded. ▪ Diagnosis: Not easy, serological tests may be helpful. Characteristic sparagnum in the subcutaneous tissue by microscopical examination. Most cases are identified post-operative. ▪ Treatment: Surgical removal. ▪ Control: Boiling or filtration of water. Avoid using frog’s or snake’s flesh as fomentations. Avoid eating raw frogs or snakes. Veterinary Helminthology 124  Order Cyclophyllidea (Eucestoda) Family Taeniidae Genus: Taenia ▪ The taeniid adult live in the small intestine of carnivores and man. T. saginata ▪ The metacestodes are cystic (cysticercus, strobilocercus, coenurus and hydatid) develops in the vertebrate intermediate host. T. solium ▪ Scolex has four cup-shaped suckers and the presence of rostellum which is armed with double rows of hook except T. saginata. T. hydatigena ▪ Single set of genital organs present in each proglottid and the genial pores are irregularly alternate. T. ovis ▪ Testes are numerous and scattered over the segments, uterus has lateral branches and the vitelline glands are in the form of a compact mass. T. pisiformis ▪ The gravid proglottids are longer than broad. The eggs are liberated by T. taeniaeformis disintegration of the gravid segments. No uterine pores. ▪ The eggs are small non-operculated, brown in colour, spherical shaped, T. multiceps mature and contain hexacanth embryo (onchosphere; not ciliated) covered by a thick and radially striated embryophore). The eggs may have an outer T. serialis envelope and a capsule, which is usually lost in faecal eggs. ▪ Two genera (Taenia and Echinococcus) are under this family. T. hyaenae Veterinary Helminthology 125  Order Cyclophyllidea (Eucestoda) Family Taeniidae Genus: Taenia ▪ The species are difficult to separate and the basis of identification is the number of lateral uterine branches in the gravid segment and the number and size of rostellar hooks. ▪ Both adult and larval stages being of importance in human health and veterinary medicine. Adult tapeworm Definitive host Larval stage Intermediate host Larval site T. saginata Man Cysticercus bovis Cattle Muscles T. soluim Man C. cellulosae Pig and man Muscles T. hydatigena Dog C. taenuicollis Sheep ,goat, cattle and pig Peritoneum T. ovis Dog C. ovis Sheep and goat Muscles T. pisiformis Dog C. pisiformis Rabbit Peritoneum T. hyaenae Dog C. dromedarii (C. cameli) Camel Muscle, liver and other organs T. taeniaeformis Cat C. fasciolaris (Strobilocercus) Mouse and rat Liver T. multiceps Dog Coenurus cerebralis Sheep, goat and man Central nervous system T. serialis Dog Coenurus serialis Rabbit and man Subcutaneous tissues Veterinary Helminthology 126  Genus: Taenia T. saginata Beef tapeworm ▪ Common name: Beef tapeworm ‘beef measles’. ▪ Final host: Man. ▪ Intermediate host: Cattle. ▪ Metacestode: Cysticercus bovis. ▪ Habitat: Small intestine (definitive host); muscle like Masseters, heart, diaphragm, tongue, liver and kidney (intermediate host). ▪ Geographical distribution: Worldwide. Particularly important in Africa and South America. ▪ Morphology: ▪ Gross: It’s the largest tapeworm of man with 5-15 m in length. The scolex is globular in shape with 4 cup shaped suckers and exceptional among the species of Taenia, has neither rostellum nor hooks. In cattle, the mature cysticercus, C. bovis, is greyish white, oval, about 1 cm in diameter, and filled with fluid in which the scolex is usually clearly visible, invaginated without rostellum nor hooks. ▪ Microscopic: Mature segment; Slightly broader than long (nearly squarish). Ovary bilobed in the posterior part of the segment. Uterus, simple tube in the median plane. Vitelline glands compact and posterior to the ovary. Testes numerous, spherical and scattered throughout the segment. The genital pores are irregularly alternating on the lateral margins of the segments. Gravid segment; The uterus has 15–30 lateral branches on each side of the central stem. Veterinary Helminthology 127 Life cycle: ▪ Life cycle: Indirect (one intermediate hosts is required). ▪ Developmental stages: The infected man passes several thousands of eggs daily either free in the faeces or as single or chain of intact gravid segments each containing about 250,000 eggs, and these can infect and survive on pasture for several months. The susceptible cattle get the infection by ingestion of grasses contaminated with the eggs. After ingestion, the onchospheres come out in intestine, and then penetrate the intestinal wall with the help of their hooks and spread throughout the striated or cardiac muscles via the blood circulation and metamorphose to cysticerci (Cysticercus bovis) which reached its fully infective form in 10-12 weeks from ingestion. Man gets the infection by ingesting raw or inadequately cooked beef meat containing the infective C. bovis. The scolex evaginates completely and attaches by suckers to the wall of intestine, the remain of metacestodes are digested away and segmentation occurs from behind the head to form strobila. ▪ Prepatent period: 2-3 months. ▪ Pathogenesis and clinical signs: Pathogenesis are related to secondary bacterial infections in injured mucosa, mechanical obstruction, nutrient competition with the host and toxin production affect the vascular and nervous system. ▪ In cattle: Under natural conditions the presence of cysticerci in the muscles of cattle is not associated with clinical signs. From the viewpoint of routine meat inspection, partial/total condemnation. Experimentally, calves given massive infections of T. saginata eggs have developed sever myocarditis and heart failure associated with developing cysticerci in the heart. ▪ In man: Intestinal disorders, hunger feeling, diarrhoea, loss of weight and weakness. Veterinary Helminthology 128 Epidemiology: ▪ Although, the infection is distributed throughout the world but more common in developing countries as a result of extensive cattle rearing and poor human sanitation. ▪ The infection rate in meat is often around 30–60% or higher and the incidence of human infection is high, in certain areas being well over 20%. Diagnosis: ▪ Cattle: Meat inspection of slaughtered animals to detect the cysticerci, usually after incision in the tongue, masseter, diaphragm, intercostal muscles and heart are examined. Anti-mortem diagnosis based on Immunoserology for screening infected herds. ▪ Human: Clinical signs, laboratory diagnosis based on stool examination to detect the eggs and the gravid segment. Segments pressed between two slides show 15-25 main lateral uterine branches. Egg; spherical, 30-40 µm in diameter, smooth thick shell with an outer brownish, radially striated embryophore which surrounds the hexacanth embryo (oncosphere). Treatment: ▪ There is no available effective drug to destroy the cysticerci in the muscle although praziquantel (50 mg/Kg orally as a single dose) has shown efficacy in experimental situations. ▪ For adult infection in man, niclosamide (2 g /person) or praziquantel (10 mg/Kg) are effective. Control: ▪ Treatment of the infected persons. ▪ Avoid cattle from grazing on pasture, fertilized by infected human manure. ▪ Proper meat inspection in slaughter houses, refrigeration of meat at -10 C for 5 days and thorough cooking of beef. Veterinary Helminthology 129  Genus: Taenia T. Solium Pork tapeworm ▪ Common name: Pork tapeworm. ▪ Final host: Man. ▪ Intermediate host: Pig and man. ▪ Metacestode: Cysticercus cellulosae. ▪ Habitat: Small intestine (definitive host); muscle of pig and occasionally in subcutaneous tissue, brain, eye, liver lung and muscle of man (intermediate host). ▪ Geographical distribution: South and Central America, India, Africa and parts of the Far East. ▪ Morphology: ▪ Gross: The adult tapeworm is 3–5 m long with a scolex, with 4 cup-shaped suckers and rostellum armed with two rows of taenoid hooks (25 – 30 hooks). In pig and man, the mature cysticercus, C. cellulosae, is milky white bladder like cyst and 6-15 X 5-10 mm in size with invaginated scolex bearing a rostellum and hooks similar to the adult. ▪ Microscopic: Mature segment; Similar to that of T. saginata but the ovary is trilobed in the posterior part of the segment, the circus sac is large and extends to the excretory vessels. The vagina don’t have a vaginal sphincter. Gravid segment; The uterus has 7–13 lateral branches on each side of the central stem. Veterinary Helminthology 130 Life cycle: ▪ Life cycle: Indirect (one intermediate hosts is required). ▪ Developmental stages: This is similar to that of T. saginata with the important differences that man, the final host, may be also become infected with cysticerci so act at the same time as intermediate and definitive host. This is most likely to occur from the accidental ingestion of T. solium eggs via unwashed hands or contaminated food. There is also a minor route of autoinfection, apparently, in a person with an adult tapeworm, from the liberation of oncospheres after the digestion of a gravid segment, which has entered the stomach from the duodenum by reverse peristalsis. Gravid segments passed in the faeces each contain around 40,000 eggs. After ingestion by a susceptible pig the oncosphere travels via the blood to striated muscle and may also develop in other organs, such as the lungs, liver, kidney and brain. ▪ Prepatent period: 2-3 months. ▪ Pathogenesis and clinical signs: ▪ In pigs: As in T. saginata, clinical signs are inapparent in pigs naturally infected with cysticerci. ▪ In man: Generally insignificant in humans with adult tapeworms (Taeniasis); Intestinal disorders, hunger pain, weakness, anaemia and diarrhoea alternating with constipation usually accompanied with increased appetite. However, when humans are infected with cysticerci (Cysticercosis), various clinical signs may occur depending on the location of the cysts in the organs, muscles or subcutaneous tissue. Cysticerci may be found in every organ of the body in humans but are most common in the subcutaneous tissue, eye ( intracranial pressure to loss of vision), brain (mental disturbances or epilepsy). Veterinary Helminthology 131 Epidemiology: ▪ In developing countries this depends primarily on the close association of rural pigs with man, and in particular, their often unrestricted access to human faeces. ▪ Poor human sanitation, improper pork meat inspection and consumption of raw or undercooked pork are the major factors in the spread of the infection. ▪ In Latin America alone it is estimated that almost 0.5 million people are affected, either by the nervous or ocular forms of cysticercosis. Diagnosis: ▪ Pigs: Meat inspection of slaughtered animals to detect the cysticerci, usually after incision in the tongue, masseter, diaphragm, intercostal muscles and heart are examined. C. cellulosae are larger and more numerous than C. bovis. ▪ Human: Clinical signs, laboratory diagnosis based on stool examination to detect the gravid segments which come out with stool in chain of 2-3 segments. They are cleared in saline and pressed between two slides to show the uterine branches (7-13). The eggs are rarely present in stool and are similar to those of T. saginata. The cysticerci in human diagnosed by scanning techniques of the affected organ. Treatment: ▪ No effective drugs are available to kill cysticerci in the pig although in man praziquantel and albendazole are considered to be of some value as possible alternatives to surgery. Control: ▪ Treatment of the infected persons. ▪ Breeding pigs under sanitary conditions. ▪ Proper meat inspection in slaughter houses, avoid eating of insufficiently cooked pork. Veterinary Helminthology 132  Cysticercosis ▪ Definition: This is the invasion of human tissues by the larval stage of T. solium (Cysticercus cellulosae). ▪ Methods of infection: 1. Ingestion of raw vegetables or water contaminated by infected faeces containing eggs of Taenia solium. 2. Auto infection: a) Internal autoinfection as a result of regurgitation of eggs released by disintegration of gravid segment into the stomach due to anti-peristalsis. b) External autoinfection as results of hand to mouth way. Infected food handlers may disseminate the eggs to healthy person’s food. ▪ Pathogenesis and signs: 1. When man is infected with cysticerci, various clinical signs may occur depending on the location of the cysts in vital organs, muscles or subcutaneous tissue. 2. Most seriously neurocysticercosis may develop when the cysticerci localize in central nervous system producing mental disturbances or clinical signs of epilepsy or intracranial hypertension. 3. They may also develop in the eye with consequent loss of vision. ▪ Diagnosis: Usually post-operative, X-ray and CAT (computerized axial tomography) and serology (IHT, IFT. ELISA) by finding the antibody to cysticerci in cerebrospinal fluid. ▪ Treatment: Praziquantel and albendazole / Surgical removal wherever possible. ▪ Control: Proper treatment of patients infected with T. solium to avoid vomiting, avoid using human manure as fertilizer and personal hygiene and periodic examination of food handlers. Veterinary Helminthology 133  Genus: Taenia T. hydatigena Taenia of Dog ▪ Common name: Taenia marginata. ▪ Final host: Dogs. ▪ Intermediate host: Ruminants and pigs. ▪ Metacestode: Cysticercus tenuicollis. ▪ Habitat: Small intestine (final hosts); abdominal cavity, liver (intermediate hosts). ▪ Geographical distribution: Worldwide. ▪ Morphology: ▪ Gross: The adult tapeworm is a large tapeworm measuring up to 5 m in length. The scolex is large and has two rows of rostellar hooks. In ruminants and pigs, the mature cysticercus, C. tenuicollis, is present in the peritoneal cavity, attached to the liver. It is thin-necked bladder containing fluid, has long neck and invaginated scolex. It is about 8 cm in diameter. ▪ Microscopic: Mature segment; Similar to that of T. saginata, Gravid segment; The uterus has 5-10 lateral branches on each side of the central stem. ▪ Life cycle: is similar to Taenia saginata. Pathogenesis: Infection is prevalent, particularly in sheep, but is detected only at meat inspection. In frequently large numbers of developing cysticerci migrate in the liver of the sheep or pig producing hepatitis cysticercosa, a condition whose gross pathology resembles acute fascioliasis, and which is often fatal. Occasionally the developing cysticerci are killed in the liver of sheep previously exposed to infection; in these cases the subcapsular surface of the liver is with greenish nodules of around 1 cm in diameter and the animal becomes weak and emaciated. The liver is totally condemned in the meat inspection. Veterinary Helminthology 134  Genus: Taenia T. ovis Taenia of Dog ▪ Common name: Ovine cysticercosis, ‘sheep measles’ ▪ Final host: Dogs. ▪ Intermediate host: Sheep and goats. ▪ Metacestode: Cysticercus ovis. ▪ Habitat: Small intestine (final host); muscle (intermediate host). ▪ Geographical distribution: Worldwide. ▪ Morphology: ▪ Gross: The adult tapeworm is large, measuring 0.5–1.5 m in length. In sheep and goats, the mature cysticercus, C. ovis, infects the musculature and cysts are usually located in the skeletal muscle, heart, diaphragm and intermuscular connective tissue. ▪ Microscopic: Mature segment; Similar to that of T. saginata, Gravid segment; The uterus of the gravid proglottids has 20–25 lateral branches on either side. ▪ Life cycle: is similar to Taenia saginata. ▪ Pathogenesis: Heavy infections in young dogs can sometimes cause diarrhoea and ill-thrift. It can be a significant cause of economic loss through condemnation at meat inspection. ▪ Diagnosis: Tapeworm infection in dogs is often recognised through the presence of shed proglottids and/or tapeworm segments in fresh faeces. ▪ Treatment: As for other taeniid species. ▪ Control: Regular treatment of dogs with an effective anthelmintic will reduce contamination of the environment. Dogs should be denied access to raw sheep and goat meat and carcases. Veterinary Helminthology 135  Genus: Taenia T. pisiformis Taenia of Dog ▪ Final host: Dogs. ▪ Intermediate host: Rabbit. ▪ Metacestode: Cysticercus pisiformis. ▪ Habitat: Small intestine (final host); peritoneum, liver (intermediate host). ▪ Geographical distribution: Worldwide. ▪ Morphology: ▪ Gross: The adult tapeworm can measure up to 2 m in length. In rabbit, the mature cysticercus, C. pisiformis, infects the liver, attach to the wall of the mesentery and omentum, small pea-like transparent cyst with an invaginated scolex. There is usually grouping of a number of cysts giving the shape of a bunch of grapes. ▪ Microscopic: Mature segment; narrow strobila with a large scolex, Gravid segment; Gravid segments have a uterus with 8–14 lateral branches on either side. ▪ Life cycle: is similar to Taenia saginata. ▪ Pathogenesis: Infection is usually asymptomatic in both the final and the intermediate host. However, in heavy infections liver damage can occur in the intermediate host as a result of migration of juvenile worms through the liver parenchyma. This can lead to hepatitis and cirrhosis. ▪ Epidemiology: There is a high prevalence in hunting dogs. ▪ Diagnosis: Infection of the intermediate host is detected through the presence of a single cyst or a cluster of several cysts in the abdominal cavity. ▪ Control: Hunting dogs should be de-wormed regularly with an effective anthelmintic and should not be fed raw carcases or offal from rabbits Veterinary Helminthology 136  Genus: Taenia T. hyaenae Taenia of Dog ▪ Final host: Dogs and Hyena. ▪ Intermediate host: Camel. ▪ Metacestode: Cysticercus dromedarii, Cysticercus cameli. ▪ Habitat: Small intestine (final host); Muscle, liver and other organs (intermediate host). ▪ Geographical distribution: Tropical Africa ▪ Morphology: Cysts are 12–18 mm in length and has an armed protoscolex with a double row of hooks. ▪ Pathogenesis and clinical signs: Infection is usually asymptomatic. Genus: Taenia T. taeniaeformis Taenia of Cat ▪ Common name: Hydatigera taeniaeformis. ▪ Final host: Cat. ▪ Intermediate host: Rats, mice and sometimes rabbits. ▪ Metacestode: Cysticercus fasciolaris, Strobilocercus fasciolaris. ▪ Habitat: Small intestine (final hosts); liver (intermediate hosts). ▪ Geographical distribution: Worldwide. ▪ Morphology: Adult is 0.5 m with large 4 suckers and armed rostellum with hooks, no neck and the segments is bell shape and 5-9 lateral branches of uterus in gravid segment. The metacestode stage is a small vesicle, pea-sized nodule partially embedded in the liver parenchyma, 1 cm in diameter, in which the scolex is not invaginated but connected to the vesicle by a segmented strobila without any genital organs (false segments) so that, the whole larva looks like a small tapeworm. On puncture, it releases yellowish material & the strobilocercus larva reaches few centimetres in length. Veterinary Helminthology 137