Most tapeworms need two different hosts to complete a life cycle. One host is the place where a parasite grows from egg to larva, called the intermediate host. The other host is where the larva become adults, called the definitive host. For example, beef tapeworms need cattle and humans to go through a complete life cycle.
The beef tapeworm eggs can survive in the environment for months or years. If a cow, the intermediate host, eats grass with these eggs on it, the eggs hatch in its intestines. The young parasite, called a larva, passes into the bloodstream and moves to muscles. It forms a protective shell, called a cyst.
When people, the definitive host, eat undercooked meat from that cow, they can develop a tapeworm infection. The larval cyst develops into an adult tapeworm. The tapeworm attaches to the wall of the intestine where it feeds. It produces eggs that pass in the person’s stool.
In this case, the cow is called the intermediate host, and the person is the definitive host.
Tapeworm infections
Humans are the definitive hosts for some species of tapeworms. They may get a tapeworm infection after eating raw or undercooked:
Larval cyst infections
Humans may be the intermediate hosts for other tapeworm species. This usually happens when they drink water or eat food with tapeworm eggs. Humans also can be exposed to eggs in dog feces.
An egg hatches in the person’s intestines. The larva travels through the bloodstream and forms a cyst somewhere in the body.
The larval cyst matures. But it won’t become a tapeworm. Cysts vary by species. Some cysts have a single larva. Others have several larvae. Or they can make more. If a cyst bursts, it can lead to cysts forming in other parts of the body.
Symptoms usually show up years after the infection began. They happen when the immune system responds to the cyst shedding debris, breaking down or hardening. Symptoms also appear when one or more cysts keep an organ from working correctly.
Exceptions
There are two exceptions to the typical life cycle of tapeworms that can infect humans.
- Pork tapeworms. Humans can be a definitive host or an intermediate host for pork tapeworms. For example, a person can have adult pork tapeworms from eating undercooked pork. The eggs pass in the person’s stool. Poor handwashing may lead to the same person or another person being exposed to the eggs. If this happens, a person can get a larval cyst infection.
- Dwarf tapeworm. The dwarf tapeworm enters humans as eggs from food or water. Exposure also may happen because of poor handwashing. The egg hatches in the intestines. The larva burrows into the wall of the intestines and forms a larval cyst. This becomes an adult dwarf tapeworm. Some eggs from the tapeworm pass in stool. Other eggs hatch in the intestine to make a repeating cycle.
Factors that may put you at greater risk of tapeworm or larval cyst infection include:
- Eating raw or undercooked meats. The main risk factor for tapeworm infection is eating raw or undercooked meat and fish. Dried and smoked fish also may have larval cysts in them.
- Poor hygiene. Poor handwashing increases the risk of getting and spreading infections. Unwashed fruits and vegetables also can carry tapeworm eggs.
- Lack of sanitation and sewage. Lack of sanitation and sewage for human waste increases the risk of livestock getting tapeworm eggs from people. This increases the risk of people eating infected meat.
- Lack of clean water. A lack of clean water for drinking, bathing and making food increases the risk of exposure to tapeworm eggs.
- High-risk regions. Living in or traveling to regions with high rates of infection is a risk factor.
From tapeworm infections
Tapeworm infections usually don’t cause complications. Problems that may happen include:
- Anemia. Long-term infection with a fish tapeworm may lead to the body not making enough healthy red blood cells, also called anemia. This can happen because the tapeworm keeps the body from getting enough vitamin B-12.
- Blockages. In some cases, a part of a tapeworm can block a duct that connects another organ to the intestines.
- Anxiety. People may be anxious or stressed about having a tapeworm infection, seeing parts of tapeworms in stool or passing long tapeworms.
- Severe allergic reaction. Larval cysts may shed debris or break down. When the immune system reacts, it may cause symptoms of severe allergy. Symptoms may include difficulty breathing, fainting, fever and a drop in blood pressure.
From larval cyst infections
Complications from larval cysts vary depending on what organ is affected. Serious complications include the following.
- Larval cysts in the brain or central nervous system. These can cause:
- Inflammation, or swelling, of the fluids and membranes surrounding the brain and spinal column, also called meningitis.
- Buildup of fluid in the brain, also called hydrocephalus.
- Pressure on the spinal cord.
- Damage to nerves, blood vessels or the brainstem.
- Larval cysts in other organs. These can lead to:
- Cyst growth that damages organ tissue.
- Bacterial disease in cysts.
- Bacterial disease related to blockages caused by cysts.
These steps can help prevent infections with tapeworms or tapeworm larval cysts.
- Wash your hands. Wash your hands with soap and water for at least 20 seconds. This is very important after using the toilet, before eating, and before and after handling food.
- Wash fruits and vegetables. Rinse fruits and vegetables under running water before eating, peeling or preparing them.
- Wash kitchen utensils well. Wash cutting boards, knives and other utensils with soapy water after contact with raw meats or unwashed fruits and vegetables.
- Don’t eat raw or undercooked meat or fish. Use a meat thermometer to make sure meat is cooked enough to kill larval cysts. Cook whole meats and fish to at least 145 degrees Fahrenheit (63 degrees Celsius) and let rest for at least three minutes. Cook ground meat to at least 160 degrees Fahrenheit (71 degrees Celsius).
- Freeze meat. Freezing meat and fish can kill larval cysts. Freeze at minus 4 degrees Fahrenheit (minus 20 degrees Celsius) or below for 7 days.
- Treat infected dogs. Treat dogs with tapeworms right away.
