Reference: Prof. Dr. Mahmoud Elseify

Dr. shimaa sobhy Ghareb

Lecture no.5II-Phylum: ApicomplexaB) Family: Sarcocystidae

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B) Family: Sarcocystidae

*In the family Sarcocystidae the species are heteroxenous• It contains the members of coccidia that form tissue cysts in the intermediate host (cyst forming coccidia).

• All members of the family produce oocyst, containing 2 sporocysts, each with 4 sporozoites.

• Oocysts are produced in the predator’s intestinal cells (final host).

• while the a sexual stages are in the tissues of the prey (intermediate) host.

1- Genus: Toxoplasma

*In this genus merogony occurs in both the intermediate and definitive hosts.

• It is facultative or obligatory heteroxenous.• Oocysts are produced in the intestinal cells of

definitive host and are not sporulated when passed. • Transmission may be either by sporulated oocysts or

by merozoites.

Toxoplasma gondii

* Intermediate hosts:• T. gondii was first found in the Gondi rat (Ctenodactylus

gundi).• It and then has since been found in over 200 species of

mammals and birds (It first described in 1909).• The intermediate host list includes rodents, insectivores, man,

pigs, sheep, horse, cat and other domestic animals and some of birds, including the chicken, pigeon and canary.

* Definitive hosts:• Only members of the family felidae have been found to be

definitive hosts of T. gondii.

• Developmental stages:• The oocysts:

• Are produced in the epithelial cells of the small intestine villi of cats and other felids only. The oocysts in cat faeces are unsporulated and spherical at first.

• After sporulation (1-4 days), they are subspherical 11-14 x 9-11 u; without micropyle, residuum, or polar granule. The sporulated oocyst contains 2

ellipsoidal sporocysts about 8.5 x 6 u, without a Stiedae body with a residuum, each sporocyst contains 4 sporozoites, these sporozoites are crescent or banana shaped, with one end pointed and the other rounded and are 8x2 u in size. The

nucleus is vesicular and more or less control. • They have all organelles of apical complex.

* Schizonts:• Occures mainly in the jejunum and ileum if cats, the nucleus of the trophozoite

divide followed by cytoplasm division leading to formation of 32 merozoites.

* Gamonts:• Most commonly occures in the ileum of cats, the macrogametocyte and

microgametocyte unit to form zygot, then oocyst which passes unsporulated in feces.

*Tachyzoites:• Tachyzoites are crescent or banana shaped, with one end pointed and the other

rounded and are 8x2 u in size. The nucleus is vesicular and more or less control. They have all organelles of apical complex.

• Occures in many types of cell of the intermediate host (Prey host), including neurons, endothelium, liver parenchyma cells, lung and glandular epithelial

cells, cardiac and skeletal muscle, foetal membranes, and leukocytes (any nucleated cell). In the acute infection they may be found free in the blood and

peritoneal exudates, the Tachyzoites are present in vacuoles formed by the host cells.

• May be around 8-16 tachyzoites together in one vacuole forming pseudocyst which measures 6-8um.

* Bradyzoites:

• Similar to Tachyzoites in shape, these are contained in cysts and occured mainly in liver, lungs and brain. The cyst may contain several thousands of

bradyzoites and measure up to 100um.

* Tissue cysts containing Zoites produced by endopolygeny in central nervous system, eye, myocardium, liver... etc.

*Modes of transmission:• Ingestion of sporulated oocyst in contaminated food, water…..with cat feces.

• spreading of the sporulated oocysts mechanically by some flies which can contaminate the food sources or water, meat…etc.

• Ingestion of tissue cysts or group of zoites containg Tachyzoites or bradyzoites in uncooked or improperly cooked meat (The bradyzoites are more infective

because they are more resistant gastric enzymes.• Congenital toxoplasmosis of the newborn resulting from infection of the mother

while she is pregnant is probably the most common form in man and perhaps sheep.

• Ingestion of transported hosts such as snails or flies which may have eaten oocysts.

• Accidentally in laboratory by wound contamination.

* By injection (the parenteral route) of merozoites. * By leucocyte transfusion.• In the last two methods, the merozoites invade the blood stream and cause a

generalized infection, susceptible tissue allover the body are invaded, and the parasites multiply in them, causing local necrosis.

• The parasitemia continues for some time, until antibodies appear in the plasma, after which the parasite disappear from the blood and more slowly from the

tissues. They finally remain only in merons (cysts) and only in the most receptive tissue.

*Pathogenicity:

• In animals: • Young animals show hepatitis, myocarditis, myositis, pneumonia,

encephalitis, diarrhoea vomiting.• Cattle:

• Mainly nervous form is dominant, but in calves, characterized by dyspnea, cough, sneezing, nasal discharges, shaking of the head and

lymph nodes enlargement especially the prescapular lymph node.• In Sheep:

• If the infection occures in the early gestation (before 55 days) causes death in foetus expulsion.

• If the infection occures in mid gestation, abortion occures with white typical lesions contain the organisms, which are 2mm in size found on

cotyledons and on foetal tissues, also retained foetus, mummified foetus can occur.

• In dogs: • Marked fever. Anorexia, diarrhea, pneumonia and neurological signs.

• In pigs: premature birth, and abortion.• In poultry: Emaciation, nervous signs and necrosis of retina with cellular

infiltration.

• In humans: • The common form of the disease is the

A- The congenital type: found in newborn infants (It is characterized by encephalitis, rash, jaundice and hepatomegaly).

B- Acquired human toxoplasmosis: This has different forms:

1- Which characterized lymphadenopathy.

2- This is typhus-like exanthemata disease (Atypical pneumonia, myocarditis and meningoencephalities and end with death.

3- Is cerebro-spinal form (fever encephalities, convulsions and lymphadenopathy followed by death.

4- Ophthalmic form (chronic chrioretintis)

5- Cutaneous toxoplasmosis: While rare, skin lesions may occur in the acquired form of the disease, including erythema multiforme-like eruptions, prurigo-like nodules,

urticaria, and maculopapular lesions.

Ocular toxoplasmosis

Cerebral toxoplasmosis

*Diagnosis:1- Isolation of the parasite by intraperitoneal inoculation to a lab.

mice after being digested in a peptic digestive fluid. But it needs at least 3 weeks to form pseudo cyst.

2- Stained smears from exudate and sections from tissues.

4- By serological tests:• ELISA: one of the most reliable tests for Toxoplasma diagnosis

also It is capable of detecting a recent infection by the estimation of IgM compared to IgG antibodies

• Sabin-Feldman dye test: The test is based on the presence of certain antibodies that prevent methylene blue dye from entering the cytoplasm of Toxoplasma organisms. (Indirect Immunofluoresence test:

*Treatment and control:• There is no satisfactory treatment, Treatment of infected

animals and man by a combination of Sulfonamides, Pyrimethamine and Spiramycin…

• Preventive measures through:

• Cooking of meat very well (to 150 °C). Wash hand with soap & water. Keeping cats indoors.

• Change litter boxes of cats & clean. Use gloves while working in garden.

• Control of rodents.

ii) Genus: Sarcocystis

*General characteristics:• In this genus, the last generation meronts (Sarcocystis cyst) are found in the

striated and heart nuscles (and rarely in the brain) and are ordinarily divided into compartments by thin internal septa.

• The a sexual stages in the intermediate hosts are meronts of two types. In perhaps all species there are one or two preliminary generations that produce

tachyzoites without a "cyst" wall. These are followed by the typical sarcocystis in the muscles (meronts). They are enclosed in a wall, some are easily visible

to the naked eye, and others are microscopic• According to the species. The large ones are known as Miescher's tubules and

they are usually cylindroid or spindle-shaped and run lengthwise in the muscles, or may be ellipsoidal or rather irregular. There are 2 types of

Sarcocystis cyst (macroscopic and microscopic cysts)• The tachyzoites and bradyzoites are elongate and resemble the merozoites of

the Eimeriidae. The oocysts and sporocysts in the definitive host resemble those of Isospora.

*Developmental stages:* The oocysts;

• these are developed in the lamina propria of the small intestine of the predator host. Where sporulation take place there the oocysts have a smooth wall, lack a micropyle,

polar granule, and residum. The sporocysts are ellipsoidal, with relatively, smooth wall; without a stiedae body, but with a residuum. The sporozoites are elongate. The

nucleus is vesicular and more or less control. They have all organelles of apical complex.

* Schizonts:• Occures mainly in endothelial cells of the blood vessels of the prey host, measures

about 2-8um.

* Gamonts:• -Most commonly occures in lamina propria of the small intestine of the predator host,

the macrogametocyte and microgametocyte produced directly from the released sporozoites, then unit to form zygot, and then oocyst passes in feces.

* Bradyzoite cyst (Sarcocyst, Miescher’s tubules or zoitocyst):• They are present in the muscles of the prey host, skeletal muscles or cardiac muscles.

It can be either microscopic or macroscopic cysts. Which appear as white streaks with spindle or fusiform shape, running in the direction of the muscles fibers. The cyst may

contain several thousands of bradyzoites and measure up to 0.5mm till few cm.

*Habitat and species: • The nomenclature is complex, usually the name includes the intermediate and

final hosts.• Sarcocystis bovicanis; the final host is dog (where the oocysts are present in

the intestine) and the intermediate host is cattle (where the cysts are present in the muscle).

• Sarcocystis bovifelis; the cat is the final host.• Sarcocystis bovihominis; the man is the final host.

• Sarcocystis ovicanis; the sheep is intermediate host.• Sarcocystis ovifelis; the sheep is intermediate host and cat is the final one.

• Sarcocystis tenella; the sheep is intermediate host.• Sarcocystis equicanis; the equines are intermediate host.

• Sarcocystis suihominis; the pigs are intermediate host and man is the final host.

• Sarcocystis dispersa; the birds are intermediate hosts.• Sarcocystis camelcanis; the camels are intermediate hosts.

*Pathogenicity:• For final host it is mild or non pathogenic results in mild

diarrhea, while in intermediate hosts (prey host) the principle pathogenic effect is due to the schizogony cycle which occures in the vascular endothelial cells, which leads to degenerative myositis.

• Also the parasite is able to produce a powerful toxin called Sarcocystin which has a selective action on the spinal cord when injected in rabbit.

• It can produce an acute lethal disease in domestic animals and abortion in sheep.

• In heavy infection it causes anorexia, fever, and anaemia.• In Ewes, S. ovicanis can cause abortion.

*Diagnosis:• Careful meat inspection at abattoir, using both

macroscopic and microscopic examinations due to presence of hidden) microscopic cysts)

• Muscle biopsy for microscopical and histological examinations

• Serological tests: ELISA and IHA and PCR

*Control:• Raw meat should not be fed to dogs

• breeding of dogs far away from livestock

iii) Genus: Besnoitia

*General characteristics:• Members of this genus are heteroxenous, producing unpopulated

oocysts in felids and multiplying by merogony in a variety of prey animals.

• Sporulation occurs outside the host (disporcystic teterazoic oocyst).

• This genus differs from Toxoplasma in that the meront wall is thick and contains a number of flattened, gaint host nuclei.

• The merozoites are banana-shaped, crescentic, or elongate ovoid, and slighty pointed at one end. They move by flexion.

They reproduce by binary fission or endodyogeny.

*Habitat and species: • Besnoitia besnoiti: Definitive host is cat while intermediate

hosts are cattle, horse, goats and other animals.

• The first generation of meronts is in the endothelial cell of the blood. The pseudocyst or cyst is found in the cells of cutis, subcutis, scleral conjunctiva, connective tissue, fascia, serosae, nasal mucosa, larynx, trachea and other tissues of the intermediate hosts.

• Trophozoites (bradyzoites) are found in the blood either extracellular or in monocytes and in smears or lymph nodes, lungs & testes.

*Life cycle:• The final host (cat) is infected by ingestion of cysts from the

intermediate host (cattle ... etc).• The merozoites develop into schizonts in the lamina propria and

intestinal epithelial cells of the small intestine.• The number of generation of schizogony has not yet been

determined.• Macrogametocytes were seen in goblet cells, while

microgametocytes not yet seen.• The oocyst is 12x17u and is shed unsporulated in cat faces and

sporulation outside (within 24 days).• The intermediate hosts are infected by ingesting the oocyst (The

cat not act as intermediate host). • The sporulated oocyst contains 2 sporocysts, each with 4

sporozoites.

*Diagnosis:• Muscle biopsy.

• Blood smear.

*Pathogenicity:• It may cause serious disease in cattle and can be divided clinically to:

a- Febrile stage in which fever, photophobia and diarrhea and swelling of lymph nodes.

b- Chronic phase: there are painful cutaneous swellings, hair thickenings, loss of hair. In sever cases death occured.

*In cattle: Most infections are mild or subclinical, characterized by the formation of numerous cutaneous and sub-cutaneous microcysts, lowering the quality of skins for the leather industry. Male sterility or impaired fertility is a common sequela in breeding bulls, and is one of the most negative aspects of the disease in animals that survive infection due to the oedema of the skin and acute orchitis.

Besnoitia cyst is present in the epididymal duct of goat

IV) Genus: HammondiaH. hammondi

*General characteristics:• Hammondia harnmondi is an intestinal coccidium of cats.

• It is structurally similar to Toxoplasma gondii.

• Unlike T. gondii, it has an obligatory two-host cycle.

• Cats are the definitive host and white mice, deer mice, rate, guinea pigs, hamster, and dogs are act experimentally as intermediate host (The nature intermediate hosts are not known).

*Other Spp.: H. heydorni and H. triffittae use canids (wolf, fox and dogs) as final host

*Life cycle:• Unsporulated oocysts are shed in cat faeces, and measure 11 x 13u.• The oocyst sporulated within, 2-3 days (22-26 °C).• The sporulated oocysts are similar to those of T. gondii.• After oral admistration of sporulated oocysts to intermediate hosts this only

method of infection, the sporozoites are released in the intestine.• Sporozoites penetrate the intestine, divide, and become tachyzoites.• The tachyzoites multiply intracellular by endodyogeny in the intestinal lamina

propria, muscularis and mesenteric lymph nodes for up to 11 days after infection causing cell necrosis.

• By day 10-11 cysts form in sketetal and cardiac muscle of mice.

* The definitive hosts (cats) become infected by ingesting cysts found in the tissues of infected intermediate hosts.

• After ingestion, bradyzoites are released from cysts and schizogony is initiated in the epithelium of the small intestine of cats.

• Merozoites released from schizonts produce male and female gametocytes. • The gametocytes and oocysts of H. hammondi resemble those of T. gondii. • The oocysts are shed 5-14 days after the ingestion of cysts.

V) Genus: Frenkelia

Frenkelia microti

*Frenkelia is a genus of parasitic protozoa in the phylum Apicomplexa. The protozoa in this genus infect the gastrointestinal tract of birds (definitive hosts) and the tissues of small rodents (intermediate hosts).

*Predator host: red tailed hawk, while the

* prey host is: Field mouse.

*Life cycle• The parasites undergo sexual reproduction in the gut of the definitive

host (a predator bird prey).

• They form cysts and are then eaten by a small rodent. Within the gut of the rodent the parasites decyst.

• They invade the intestinal wall and are carried to the liver. They undergo schizogony in the hepatocytes and Kupffer cells.

• They then invade the nervous tissue of the rodent host forming cytic structures.

• The infected rodent is then eaten by a bird when the tissue cysts are digested releasing the parasites.

• The parasites invade the enterocytes, undergo merogony and Gametogony. Gametes are formed which then fuse forming a zygote that undergoes encystations.

V) Genus NeosporaNeospora caninum

*Neospora is an important pathogen in cattle and dogs. It was not discovered until 1984 in Norway, where it was found in dogs. It is highly transmissible and some herds can have up to a 90% prevalence.

*Final host: Dog, coyotes and gray wolves.

*Intermediate hosts: cats, sheep and cattle, fox and other animals

*Life cycle:• The life cycle is similar to Toxoplasma. An infected

dog will pass the oocysts through its feces and infect food or water.

• A cow or other animal will then up take the parasite. The parasite will undergo asexual reproduction in the animal's muscle until it is eaten by a dog. There, sexual reproduction will occur and oocysts will be created and passed through the feces

*Epidemiology:

• Dogs are often the definitive host but can act as an intermediate host as well.

• Cows are usually the intermediate host. No horizontal cow-to-cow transmission have been shown, although salival interactions have been suggested.

• Vertical transmission can occur when an infected cow gives birth to an infected calf; the calf survives the infection and grows into an adult.

*Pathogenicity: • In cattle: it causes storms of abortion, low milk yield, and are

more likely to suffer retained fetal membranes. The overall economic effect of Neospora infection in a herd is not clear, although direct costs are due to abortion, infertility, returns to service and loss of milk yield and indirect costs through replacements.

• Symptoms in dogs: clinical signs of Neosporosis are usually focused to neural and muscular tissues in the dog, but can also include the heart, liver, lungs and skin. The most severe and frequent infections – including the ones that lead to ascending paralysis of the limbs – are seldom seen in adult dogs; 

*Diagnosis: ELISA, IFAT (immunofluorescent antibody test)