Taenia saginata (beef tapeworm)
Diagnostic Form:
The diagnostic form is the egg found in the concentrates of formalin preserved stool. The eggs are 31-43 µm in diameter, spherical with a characteristic thick striated shell and brown in color. The eggs are indistinguishable from those of Taenia solium.
When passed in the stool, the eggs are embryonated with a 6-hooked oncosphere contained inside the thick shell.
The scolex of Taenia saginata will characteristically have four suckers and lack a rostellum with a double crown of hooks. Taenia solium on the other hand will have four suckers and a rostellum with a double crown of hooks which functions to secure the nematode securely to the intestinal wall of the host. The scolex however is rarely obtained from either nematode for analysis.
Species differentiation of Taenia solium and Taenia saginata should be made from proglottids where species differentiation can be made by counting the uterine branches. When the proglottids have the uterine branches stained (as with india ink), the branches become visible. Taenia saginata uteri will have twelve or more uterine branches on each side while Taenia solium will only have five to ten uterine branches.
Geographic Prevalence:
The parasite is prevalent in Africa, South East Asia, South America, and some areas of Eastern Europe.
Disease It Causes And The Clinical Symptoms:
The infections fare generally asymptomatic but in heavy infections there can be a myriad of symptoms. These symptoms include abdominal discomfort, diarrhea, nausea, loss of appetite with weight loss, constipation, and headaches.
Infections can become so heavy that intestinal obstruction can occur neccesitating the need for surgical removal of the worm burden.
Antigens released by the worms can also innitiate an allergic reaction in the infected individual.
Location In The Host:
The intestine.
Primary Vector:
None. Resevoir is cattle and humans. The prevalence of the parasite is generally favored by an evironment in which cattle are raised by infected humans and there is poor hygiene, meat is improperly cooked or eaten raw, and the inspection of meat is poor.
Life Cycle:
Test Recommended For Detection/Diagnosis:
Detection/diagnosis is from an ova and parasite examination of fresh stool. The stool is examined for the presence of eggs. Eggs can only identify to the family Taeniidae and not to the species level. Therefore it is important to have the scolex and or a gravid proglottid to help in identifying Taenia saginata.
Histological observation of the uterine branches will most assuredly make a definitive identification. Taenia saginata's uterus stems out from its center and has 12 to 20 branches as oppose to Taenia solium's uterus that is far less in number and thicker.
Taenia solium (pork tapeworm infection or cysticercosis)
Diagnostic Form:
The diagnostic form is the egg found in the concentrates of formalin preserved stool. The eggs are 31-43 µm in diameter, spherical with a characteristic thick striated shell and brown in color. The eggs are indistinguishable from those of Taenia saginata.
When passed in the stool, the eggs are embryonated with a 6-hooked oncosphere contained inside the thick shell.
The scolex of Taenia solium will characteristically have four suckers and a rostellum with an impressive double crown of hooks which functions to secure the nematode to the wall of the host intestine (see above). Taenia saginata on the other hand will have four suckers but will not have the double crown of hooks. The scolex however is rarely obtained from either nematode for analysis.
Species differentiation of Taenia solium and Taenia saginata should be made from proglottids where species differentiation can be made by counting the uterine branches. When the proglottids have the uterine branches stained (as with india ink), the branches become visible. Taenia saginata uteri will have twelve or more uterine branches on each side while Taenia solium will only have five to ten uterine branches.
Geographic Prevalence:
The parasisite is found in Africa, Asia and Latin America where there are areas with poor sanitation and free ranging pigs that have access to human feces.
The disease is uncommon in the United States but it can occurr by the ingestion of tapeworm egg contaminated food that has been prepared by an asymptomatic tapeworm carrier with poor hygiene. There has been an increase in the incidence of neurocysticercosis in the United States due to an influx of refugees from areas where the disease is endmic such as Burma, Lao People's Democratic Republic, Bhutan, and Burundi where the seroprevalence is high.
Disease It Causes And The Clinical Symptoms:
The parasite causes two recognized diseases, taeniasis and cysticercosis. Taeniasis is the term used to describe the inestinal tapeworm disease while cysticercosis is the term used to describe the central nervous system disease caused by larval cysts infecting the brain and/or central nervous system. The larval cysts can also infect other areas of the host such as muscle, eyes, and other tissue.
Taeniasis can cause vague abdominal discomfort. In many individuals the infection is asymptomatic.
Neurocysticercosis however is a serious form of infection which can lead to seizures, headaches, confusion, vertigo, hydrocephalus, and even death. This is generally the primary cause of illness. Individuals who have lived in or have traveled to where the seroprevalence is high and present with neurological symptoms should be suspected of neurocysticercosis.
Cysticercosis with muscle involvement do not generally cause any symptoms but will produce palpable lumps under the skin that can cause some discomfort when pressed on and be cosmetically unappealing.
Location In The Host:
The tapeworm is generally located in the intestine in the case of taeniasis and is acquired by the ingestion of infected pork meat which is raw or undercooked.
In cysticercosis the disease is obtained by the ingestion of embryonated eggs. The oncospheres hatch from the eggs and penetrate the intestinal wall and circulate to musculature. Larva (oncospheres) however can migrate to other areas of the host body such as eye, and other tissue. Most importantly is the ability for it to migrate into the brain and central nervous system. Once there they develop into cysticerci and produce the disease cysticercosis.
Primary Vector:
None. Pigs and humans act as natural reservoirs and hosts to the parasite.
Life Cycle:
Test Recommended For Detection/Diagnosis:
Tapeworm infections (taeniasis) is detected/diagnosed by an ova and parasite examination. Egg shedding is variable and as such it is recommended that three specimens be submitted for analysis over a one week period.
Neurocysticercosis is more difficult to diagnosis and will require an MRI and/or CT brain scan in conjunction with blood tests. Blood tests alone are not reliable as light infections are many times negative.
Hymenolepis nana (dwarf tapeworm)
Diagnostic Form:
The eggs are the main diagnostic form of the parasite. The eggs are are ovoid to circular in shape and measure approximately 30µ to 47µ in diameter. The eggs are composed of a outer transparent shell and an embryonic oncosphere that is centrally suspended in a gelatinous layer. The oncosphere has three pairs of hooks characteristic of all larval cestodes. The membrane carries two polar knobs with 4 to 8 filaments attached to each knob.
On occassion mature proglottids can be obtained. The proglottids are short and wide, 0.22 by 0.85 mm. Each of the proglottids usually contain around 200 eggs. The proglottids are hermaphroditic with a central lobed ovary and three round testes. Gravid proglottids will normally break off and disintegrate to release the infective eggs.
The head of the adult tape worm, the scolex, is 0.3 mm wide and bears four suckers with a retractable rostellum arm containing a ring of 20 to 30 backward-pointing hooks which ensure the attachment of the worm to the intestinal mucosa. The adult worms are seldom recovered for identification.
Geographic Prevalence:
This tapeworm has a higher rate of infection in children that in adults mainly due to the transmission occuring via the fecal - oral route. That being said, the parasite is considered cosmopolitan in distributoin but is more common in the in temperate regions of the world than in the tropics.
Disease It Causes And The Clinical Symptoms:
Hymenolepsis, or dwarf tapeworm infection, induce gastrointestinal disturbances and allergic reactions in the host. The infection is transmitted from human to human or the ingestion of contaminated water or food. Some symptoms include anorexia, headache, abdominal pain, diarrhea, and generalized weakness. An eosinophilia may be present in the hematologic findings of the host due to an allergic reation to the parasite. Epileptoid convulsions and/or irritability can occur. In small children it is not uncommon for autoinfections to produce infections that can last for years.
Allergic reactions due to the antigens of the parasite can cause necrotioc ulcerations of the conjunctiva and cornea in up to 73% of children with Hymenolepsis nana infections.
Hosts with immune systems that are compromised may exhibit extraintestinal manifestations of the parasitic infection. Invasive disease in these patients is possible to all organs of the body.
Location In The Host:
Small intestine
Primary Vector:
None. Man is usually the resevoir for this parasite. The closely related Hymenolepsis diminuta has the rat-mouse as the resevoir and requires an arthropod as an intermediate host (flea, flour beeyle, earwig or millipede). Infection is acquired by the accidental ingestion of an infected arthropod. Hymenolepsis diminuta is normally asymptomatic.
Test Recommended For Detection/Diagnosis:
The test of chioce for the detection/diagnosis is the ova and parasite examination of stool specimens. Three stool specimens collected consecutively on three different days should be submitted for the optimal detection of eggs in the stool. Stools should be submitted in the proper preservatives for ova and parasite examination.
Hymenolepis diminuta
Diagnostic Form:
The eggs are the main diagnostic form of the parasite. The eggs are are ovoid to circular in shape and measure approximately 30µ to 47µ in diameter. The eggs are composed of a outer transparent shell and an embryonic oncosphere that is centrally suspended in a gelatinous layer. The oncosphere has three pairs of hooks characteristic of all larval cestodes. The membrane carries two polar knobs. This species has no polar filaments.
On occassion mature proglottids can be obtained. The proglottids are short and wide (wider than longer), 0.22 by 0.85 mm. Each of the proglottids usually contain around 200 eggs. The proglottids are hermaphroditic with a central lobed ovary and three round testes. Gravid proglottids will normally break off and disintegrate to release the infective eggs.
The head of the adult tape worm, the scolex, is 0.3 mm wide and bears four suckers with a retractable rostellum arm containing a ring of 20 to 30 backward-pointing hooks (not visible) which ensure the attachment of the worm to the intestinal mucosa. The adult worms are seldom recovered for identification.
Geographic Prevalence:
This tapeworm has a higher rate of infection in children that in adults mainly due to the transmission occuring via the fecal - oral route. That being said, the parasite is considered cosmopolitan in distributoin but is more common in the in temperate regions of the world than in the tropics.
Disease It Causes And The Clinical Symptoms:
Hymenolepsis diminuta infections, unlike those of Hymenolepsis nana infections, are largely asymptomatic with occassional patients complaining of some abdominal distress. Infection is acquired by the accidental ingestion of infected arthropods which serve as intermediate hosts between the reservoir, rat-mouse.
Location In The Host:
Small intestine.
Primary Vector:
Hymenolepsis diminuta has the rat-mouse as the resevoir and requires an arthropod as an intermediate host (flea, flour beetle, earwig or millipede). Infection is acquired by the accidental ingestion of an infected arthropod. Hymenolepsis diminuta infections are normally asymptomatic.
Test Recommended For Detection/Diagnosis:
The test of chioce for the detection/diagnosis is the ova and parasite examination of stool specimens. Three stool specimens collected consecutively on three different days should be submitted for the optimal detection of eggs in the stool. Stools should be submitted in the proper preservatives for ova and parasite examination.
Echinococcus granulosus
Diagnostic Form:
The cyst is the diagnostic form and it is usually found in the liver or lung of the human host. The cyst are normally detected by radiological methods. A thorough clinical history and immunological testing can confirm the suspicion of the radiological test results.
These cyst are large sacs that contain the scoleces, daughter cysts, hooks and calcareous corpuscles of the worm. The contents of the cyst are extremely allergenic and can induce a fatal anaphylactic reaction in patients if the cyst were to rupture. For this reason the surgical removal of cyst require great care in avoiding their rupture.
Geographic Prevalence:
Mostly seen in Mediterranean countries but the parasite is considered cosmoplotan in distribution with human infections primarily seen in sheep-raising areas where domestic dogs are used in herding.
Disease It Causes And The Clinical Symptoms:
The parasitic disease is named echinococcosis, hydatid cyst, hydatid disease and hydatidosis. Some of the early clinical signs of infection are dependant on the location of the cyst as well as the size of the cyst. For example, cysts located in the liver can cause jaundice or portal hypertension once the cyst attains a large enough size (sometimes up to a year). Cysts in the lung can produce shortness of breath, coughing and chest pain with symptoms becoming more pronounced as the cyst gets larger. Alergic reactions due to the presence of cyst antigens can produce eosinophilia, urticaria and bronchospasm in the host.
Surgical intervention is necessary to remove the cyst but this must be done with great care. The accidental release of the contents of the cyst into the host can lead to anaphylactic shock and death.
The growth and location of the cyst are many times in a position within the host where the cyst may be easily prone to rupture spontaneously in which anaphylactic shock and death may also occur.
Location In The Host:
The main location of the organism is the liver, spleen, kidney, and lung and is in the form of a growing cyst.
Primary Vector:
None. Sheep are the resevoir and dogs serve as an intermediate host. Humans can be described as accidental intermediate hosts. Humans as an intermediate host, ingest material contaminated by feces from a carnivore; as a definitive host, ingestion of uncooked meat (offal) from a herbivore.
Life Cycle:
Test Recommended For Detection/Diagnosis:
Serological tests serve to help in making a diagnosis along with a good clinical history. The confirmation of a cyst in the liver and/or lung by radiologic methods is also useful.
Surgical biopsy of the mass to extract hydatid cyst fluid can be done to examin for the presence of scolices, brood capsules, hydatid sand, or daughter cells, but is highly discouraged because the procedure has a high risk for the release of hydatid cyst fluid into the host leading to anaphylactic shock and/or death.
Diphyllobothrium latum
Diagnostic Form:
The diagnostic form is the egg found during ova and parasite exminations of the stool. The eggs are fairly numerous in the stool however few eggs are produced at the beginning of the patent period in the egg-discharging periodicity.
The egg is ovoid in shape, thin shelled, measure 60 to 70 µm by 40 to 50 µm, and is yellowish brown in color. There is a characteristic "knob" at the abopercular end of the egg and an operculum present at the other end. See below:
The adult worm itself is 2 to 15 m long with a width of about 20 mm. There are about 3,000 proglottids. The examination of the gravid proglottid, if obtained, will also provide a definitive diagnosis. Proglottids are wider than longer and have a centrally located rosette uterine structure. The anterior of the uterus contains fully-developed eggs and forms four to eight large loops to each side of the midline. The anterior of the uterus will contain fully developed eggs.
The scolex has dorsal and ventral depressions called "bothria" which serve as holdfast and locomotor organs. These sucking grooves are almond shaped. No hooks are present.
Geographic Prevalence:
The parasite is commonly encountered in the subarctic and temperate regions of the Northern Hemisphere. The consumption of raw fish or fish products is always found to be responsible for infections due to Diphyllobothrium latum. Because of the importation of these products to other areas of the world, one cannot rule out infections occuring elsewhere.
Disease It Causes And The Clinical Symptoms:
Clinical symptoms vary. Some individuals experience little symptoms at all. But in those patients exhibiting symptoms, the symptoms include the following: epigastric pain; mild fever; weakness and/or fatigue; cravings for salt; hunger; diarrhea; numbness of extremities.
The worms on occassion can produce intestinal obstruction. Vomiting of worms can occur. Acute pain to the abdominal area can also be a symptom.
The worm can in some cases also cause the malabsorption of folates and/or vitamin B12 due to either competition for available nutrients or a direct mechanical irritation of the intestinal mucosa causing a malabsorption syndrome. This condition is sometimes referred to as "tapeworm pernicious anemia".
Location In The Host:
Most commonly attaches to the wall of the ileum. Less commonly it can attach to the jejunum. Rarely it will find its way to other levels.
Life Cycle:
Primary Vector:
None. The parasite requires a 1st intermediate host, a copepod, for the procercoid stage. A 2nd intermediate host, fish, for the plerocercoid stage. Large predatory fish feeding on smaller fish that consume the copepods, then become infected with large amounts of plerocercoids. These large predatory fish are the carriers or paratenic hosts.
The final host, man, is infected by ingesting raw or insufficiently cooked fish. At about the third week or later eggs begin to appear in the stool. Eggs are thereafter discharged periodically according to negative phases and patent periods of irregular intervals of egg discharge. Other animals can serve as a final host to the parasite such as dogs, cats, and pigs. Studies have also found other mammals such as bear, foxes, wolves to be hosts.
Test Recommended For Detection/Diagnosis:
The detection of the charateristic eggs in an ova and parasite examination is the best method for detection and diagnosis. Since the discharge of eggs can be atirregular intervals, it is important to have at least three different stool specimens submitted for examination, collected at three separate days.
The examination of the proglottids, if obtained, will also provide a definitive diagnosis. Proglottids have a seminal vesicle visible from the ventral side, which is situated dorsally and caudally to the cirrus sac. The anterior of the uterus contains fully-developed eggs and forms four to eight large loops to each side of the midline.
