What Are Tapeworms? What Causes Tapeworm Infection?

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Main Category: Infectious Diseases / Bacteria / Viruses
Also Included In: GastroIntestinal / Gastroenterology;  Primary Care / General Practice;  Tropical Diseases
Article Date: 10 Nov 2009 - 0:00 PST

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Tapeworms, or cestodes, are intestinal parasites; they are worms that are flattened like a tape measure. A tapeworm cannot live freely on its own - it survives within the gut (intestine) of an animal, including a human.

A parasite is an animal or plant that lives in a host; another animal or plant.

Tapeworm eggs generally enter the human host from animals through ingested food, especially raw or undercooked meat. Humans can also become infected if there is contact with animal stools or contaminated water. When an infection is passed from an animal to a human it is called zoonosis.

Most people who have a tapeworm experience no symptoms and are unaware of hosting one. If signs and symptoms are present, they usually include tiredness, abdominal pain, weight loss and diarrhea.

A human who has a tapeworm will need treatment to get rid of it. Treatment is 95% effective and lasts just a few days.

The most common tapeworms to infect humans in Western Europe and USA/Canada are:

• Taenia solium - the pork tapeworm. Also known as the armed tapeworm or measly tapeworm.


• Taenia saginata - the beef tapeworm. Also called the unarmed tapeworm.


• Hemynolepis nana - the dwarf tapeworm.

Taenia solium and echinococcus granulosus (dog tapeworm) can cause other illnesses if their larvae get out of the host's intestine and settle elsewhere in the body.

According to the National Health Service (NHS), UK, in 2005 there were 71 reported incidences of beef and pork tapeworms among humans in England and Wales, and just 1 in Scotland. Authorities do not know whether the hosts became infected in the UK or while they were abroad. There were 11 cases of hydatid disease, an infection caused by the dog tapeworm in England and Wales in 2005 - two of these people had had a recurrence of the disease.

According to the CDC (Centers for Disease Control and Prevention), USA, tapeworm incidence in the USA has been rising, mainly because of increased raw fish consumption.

According to Medilexicon's medical dictionary, a tapeworm is:

"An intestinal parasitic worm, adults of which are found in the intestine of vertebrates; the term is commonly restricted to members of the class Cestoidea. Tapeworms consist of a scolex, variously equipped with spined or sucking structures by which the worm is attached to the intestinal wall of the host, and strobila having several to many proglottids that lack a digestive tract at any stage of development.

The ovum, entering the intestine of an appropriate intermediate host, hatches and the hexacanth penetrates the gut wall and develops into a specific larval form (cysticercoid, cysticercus, hydatid, strobilocercus), which develops into an adult when the intermediate host is ingested by the proper final host. A three-host cycle with a swimming coracidium, procercoid and plerocercoid (sparganum) larva, and adult intestinal worm is found in aquatic life cycles, as in Diphyllobothrium latum (broad fish tapeworm) and other pseudophyllid cestodes.

Other important species of tapeworm are Echinococcus granulosus (hydatid tapeworm), Hymenolepis nana or H. nana var. fraterna (dwarf or dwarf mouse tapeworm), Taenia saginata (beef, hookless, or unarmed tapeworm), T. solium (armed, pork, or solitary tapeworm), and Thysanosoma actinoides (fringed tapeworm of sheep)."

What are the risk factors for tapeworms?

A risk factor is something that increases the risk of developing an illness, condition or infection. For example, poor dental hygiene increases the risk of developing gum disease. Therefore, poor dental hygiene is a risk factor for gum disease. The following are considered risk factors for tapeworm infection:

• General lack of hygiene - if you wash your hands infrequently the risk of transferring infection into your mouth is greater.


• Working with or exposure too animals - this is especially the case in areas where feces are not disposed of effectively.


• Traveling to or living in certain parts of the world - countries, and parts of some countries where sanitation practices are poor, the risk of becoming infected with a tapeworm is much greater.


• Consuming raw or undercooked meats and fish - larvae and eggs present in meats and fish may infect people if eaten raw or undercooked. Experts say that sushi (raw fish) is safe if it has been frozen beforehand - the risk with fish is mainly freshwater fish.

What are the signs and symptoms of tapeworm infection?

A symptom is something the patient feels and reports, while a sign is something other people, including a doctor or nurse may detect. For example, pain may be a symptom while a rash may be a sign.

It is not uncommon for an infected person to have no apparent signs and symptoms. Even if symptoms are present, they may be so mild that many people believe they are caused by something else.

If signs or symptoms are present, they may include the following (may vary depending on the type of tapeworm):

• Eggs, larvae or segments from the tapeworm in stools. The segments will contain tapeworm eggs.


• Abdominal pain. This may include epigastric pain - pain in the abdomen, just above the stomach.


• Vomiting


• Nausea


• General weakness


• Inflammation of the intestine (enteritis), which often causes diarrhea as well.


• Diarrhea


• Weight loss


• Altered appetite - sometimes there may be a loss of appetite. Hosts with the pork tapeworm may experience a rise in appetite.


• Sleeping difficulties


• Dizziness


• Convulsions


• Malnutrition - because the tapeworm is grabbing an important proportion of essential nutrients.


• Vitamin B12 deficiency - this is very rare and only among hosts infected with Diphyllobothrium latum (fish tapeworm)

Invasive infection signs and symptoms

If the tapeworm larvae made their way out of the intestines and formed cysts in tissues elsewhere in the body, there is a risk of tissue damage. The following symptoms may be possible:

• Fever
• Abdominal pain or discomfort
• Jaundice
• Cystic lumps or masses
• An allergic reaction to larvae
• Bacterial infections
• Seizures and other neurological symptoms
• Blindness
• Intracranial pressure (pressure inside the skull

Signs and symptoms will depend on what type of tapeworm it is, how severe the infection is, and which tissues (which part of the body) are infected.

What are the causes of tapeworm infection?

In human beings, tapeworm infection is most commonly caused by:

The pork tapeworm (Taenia solium), beef tapeworm (Taenia saginata), dwarf tapeworm (Hymenolepis nana), and fish tapeworm (Diphyllobothrium latum) from raw freshwater fish.

Most people become infected after ingesting tapeworm eggs or larvae.

• Ingestion of eggs - eggs get into humans via food, water or contaminated soil (mainly contaminated with infected animal feces). If a host, such as a pig, has a tapeworm inside, proglottids (worm segments) or eggs may be present in its feces, which drop onto the soil. Each segment may have thousands of eggs. A human can become infected by drinking contaminated water, being close to the animals and contaminated soil, or consuming contaminated food. The eggs hatch into larvae (baby tapeworms) and make their way into the gut, or even outside and infect other parts of the body. This type of infection is most common with tapeworms that come from infected pigs, and much less common if the original host was cattle or fish.


• Eating infected meat/fish - if the meat or fish has larvae cysts and is undercooked or raw, they can reach the intestine where they mature into adult tapeworms. An adult tapeworm can live as long as 20 years, they can also be up to 50 feet long. Many of them attach themselves to the walls of the intestine, while others will go straight through the digestive system and end up in the toilet when the human passes a stool.
  
  Fish tapeworm infection is more common in countries where the consumption of raw fish is common practice, such as Eastern Europe, Scandinavia and Japan. Undercooked or raw freshwater fish, such as salmon, are the most common sources.


• Human-to-human transmission - the dwarf tapeworm can be transmitted from human-to-human. It is the only tapeworm that can go through its entire life cycle, eggs-larvae-mature tapeworms, in one single host. Dwarf tapeworm infection is the most common tapeworm infection globally.


• Insect-to-human transmission - fleas and some types of beetles may pick up the eggs by eating the excrements (droppings) of infected rats or mice. These insects can infect humans. The insects are called intermediate hosts - the tapeworm exists in them in between the egg and adult stages. This type of infection occurs with dwarf tapeworms, and is much more common in areas where hygiene practices are poor.


• Re-infecting yourself - during treatment humans can reinfect themselves if they do not follow good hygiene practices. The eggs will be present in the human stools. If the individual does not wash his/her hands after going to the toilet, there is a risk of reinfection.


• Dog tapeworm - called echinococcosis, hydatid disease, or unilocular hydatid disease. Unilocular means the tapeworm larvae (cyst containing larvae) settles and stays in just one place in the body. Humans, especially children, may accidentally touch dog stools and eventually swallow the eggs when they touch their mouths with their hands. Infection is also possible by having close contact with dogs.
  
  This type of tapeworm is more common in some parts of Australia, Greece, southern Spain, North and South America, Turkey and Asia. It is also more common in rural, rather than urban areas. The National Health Service, UK, says that hydatid disease is rare in the UK, with virtually all cases occurring in sheep-farming areas.

Diagnosing tapeworm infection

Any individual who suspects tapeworm infection, or has the signs and symptoms described above should see their GP (general practitioner, primary care physician). Some patients may notice infection themselves by checking their stool for parts of the adult tapeworm. However, a doctor is still needed to check the stool (by sending samples to a lab).

Diagnosis of adult tapeworms - this is done by searching for and detecting eggs, larvae or segments of tapeworms in the patient's stool. If infection is with a pork or beef tapeworm the segments will be motile (they wiggle, move). The patient will be asked to provide a sample of his/her stool in a sterile container.

Laboratories may use microscopic identification methods to try to detect eggs or tapeworm segments in the feces. It may be necessary to collect two or more samples over a given period to detect the parasite because eggs and tapeworm segments are not released in a regular pattern into the stool.

The doctor may also examine the area around the patient's anus for signs of eggs or larvae.

Diagnosing tapeworm larvae infection - the following diagnostic aids may be used, depending on the type of tapeworm larvae infection:

• Blood tests - the aim here is to look for antibodies to infection.


• Imaging scans - this could include a chest X-ray, ultrasound scan, computerized tomography (CT) scan, or a Magnetic Resonance Imaging (MRI) scan.


• Organ tests - the doctor may want to check that the organs are working properly.

What are the treatment options for tapeworm infection?

Treating tapeworm larvae infection is more complicated than treating an adult tapeworm infection. While the adult tapeworm stays in the gut, the larvae may settle in other parts of the body. When larvae infection finally produces symptoms, the infection may have been present for years. In some rare cases larvae infection can be life-threatening.

• Oral medications for treating tapeworms - oral medications such as, praziquantel (Biltricide) or albendazole (Albenza), and niclosamide may be prescribed. Niclosamide is not currently available in the USA (November, 2009). In the UK, niclosamide and praziquantel are only available on a named-patient basis - because tapeworm infections in the UK are so rare, the doctor or pharmacist may have to make special arrangements to get hold of the medication.
  
  Our digestive system does not absorb these drugs well. They either dissolve or attack (and kill) the adult tapeworm.
  
  The tapeworm's scolex (neck and head) needs to come out of the patient's intestine in their stools. If the scolex is not destroyed the tapeworm can grow again.
  
  A doctor may advise the patient to take a laxative to help the tapeworm come out in the stools. If the patient has a pork tapeworm infection, in order to prevent vomiting, which can lead to reinfection by swallowing the tapeworm larvae, they may be given an anti-emetic (prevents vomiting) medication.
  
  These medications to do not target the eggs. It is therefore very important for patients to wash their hands thoroughly after going to the toilet and before eating so that they do not reinfect themselves.
  
  The patient's stools will be checked several times one to three months after the course of medication. These medications, if procedures are followed properly, are 95% effective.
  
  Medication used for treating adult tapeworm infection is often referred to as anthelmintic medication. Anthelmintic means that it kills the parasitic worm, and makes the worm pass out of the gut in the patient's stools.


• Anti-inflammatory medication - if the infection affects tissues outside the intestine, the patient may have to take a course of anti-inflammatory steroid to reduce swelling caused by the development of cysts.


• Surgery - if the patient has life-threatening cysts that have developed in vital organs, such as the lungs or liver, surgery may be required. The doctor may inject a cyst with medication, such as formalin, to destroy the larvae before removing the cyst. In some cases the patient may need organ transplantation. If surgery to remove a cyst is not possible because it is too close to major blood vessels or organs, the doctor may prescribe albendazole to try to slow down or control the cyst's growth.

What are the possible complications of tapeworm infection?

The risk of complications depends on several factors, including the type of tapeworm and whether or not the patient receives treatment.

• Beef tapeworm - as the beef tapeworm lives in the gut and can easily be treated it is relatively harmless.


• Cysticercosis - if a human ingests pork tapeworm eggs there is a risk of larvae infection (cysticercosis). The larvae can exit the intestine and infect tissues and organs elsewhere in the body, resulting in lesions or cysts. Lesions or cysts can eventually affect the normal function of an organ. In some cases they can rupture.


• Neurocysticercosis - a dangerous complication of pork tapeworm infection. The brain and nervous system are affected. The patient has headaches and vision problems, as well as convulsions (seizures), meningitis, and possibly dementia. In very severe cases the infection can be fatal.


• Echinococcosis (hydatid disease) - the echinococcus tapeworm, which is most commonly found in sheep and dogs, can cause an infection called echinococcosis. The larvae leave the gut and infect organs, most commonly the liver. The infection can result in large cysts, which place pressure on nearby blood vessels and affect circulation. Sometimes the blood vessels may rupture. In severe cases surgery or liver transplantation is required. Infection may start during childhood, but symptoms may not become apparent for many years.

Prevention

• Good hygiene - wash your hands thoroughly with soap and water after using the toilet and before eating.


• Food precautions - if you are in an area where tapeworms are common, make sure you wash and cook all fruits and vegetables with clean water.


• Livestock - properly dispose of animal and human feces. Minimize animal exposure to tapeworm eggs.


• Meat - cook meat to a temperature of at least 66C (150F) thoroughly. This will kill larvae or eggs.


• Meat and fish - freeze fish for at least 24 hours and meat for at least 12 hours. This will kill tapeworm eggs and larvae.


• Raw foods - do not consume raw or undercooked pork, beef and fish.


• Dogs - make sure your dog is treated for tapeworms. Follow your veterinarian's advice about treating your dog regularly with de-worming medication. Take special care with your own personal hygiene. Sheepdogs are especially vulnerable to tapeworm infection because sheep are intermediate hosts for the dog tapeworm. Make sure your dog only eats cooked meat and fish.


• Kitchen hygiene - make sure all work surfaces are regularly cleaned and disinfected. Do not allow raw foods to touch other foods. If you have touched raw meat/fish wash your hands before moving on to touching other things.

Experts say that smoking or drying meat or fish are not considered reliable ways of killing larvae or eggs.

Written by Christian Nordqvist


Copyright: Medical News Today
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