Tapeworm Life Cycle

A tapeworm infestation of Taenia pisiformis in rabbits is actually called Tapeworm Cyst Infection, or Cysticercosis Pisiformis. This is because in a rabbit, the tapeworm goes from an egg, to a larva, to an immature tapeworm that resides in a ‘cysticercus’ in the rabbit, but not all the way to a mature tapeworm.

The tapeworm life cycle starts with the adult tapeworm (T.pisiformis), which inhabits the intestines of the dog, coyote, wolf or fox. The adult tapeworm sheds its eggs, and the infested canine excretes tapeworm eggs in their scat or feces.

Stage II of the tapeworm life cycle is the transmission of the eggs to the intermediate host, most often a rabbit, rodent or hare. This occurs through contamination of their fur with dog feces, or through contaminated food. Wild cottontails easily pick up tapeworm eggs as they run through the brush, and then meticulously groom themselves, eating the eggs.

The same mode of infection can be true of those domestic rabbits allowed to run in the same space as the family dogs. In the case of caged rabbits however, it is more likely that they ingest tapeworm eggs through contaminated hay.

Stage III of the tapeworm life cycle is the larval stage. In the rabbit’s guts, the eggs hatch, and the larvae migrate to the liver. It takes the larvae 15-30 days to mature to their next phase - a 'cysticercus' (plural = cysticerci) or fluid-filled cyst. During the 15-30 days, the larvae are changing and maturing, while they migrate through the liver. Sometimes they leave scars on or within the liver.

Stage IV of the tapeworm life cycle is the formation of multiple cysticerci within the secondary host - the rabbit. Cysts measure up to 2-3 cm (1 1/4 inches).

A cysticercus looks like a small balloon filled with clear fluid. They vary in size from that of a pea, to the size of your fingertip.

(Pictured is a rabbit's liver. The dark green object is the gallbladder; the whitish balloon in the center of the picture is a cysticercus (pictures courtesy of the rabbit breeder). The head of the immature tapeworm, or scolex, is to the right within the cyst. Also see pictures below from the same rabbit.)

Normally, you might find one or a few of these cysts (on average around 6-10) attached to the surface of the liver, intestines, lining of the gut and even the lungs. Each cysticercus contains a white floating head (scolex) of an immature tapeworm. Older cysts may be pus-filled.

(Pictured to left - the contents of a tapeworm cyst.)

Depending upon the severity of the infection, the rabbit may develop hepatitis leading to acute death or chronic wasting. It is possible for cysticerci to form in other areas of the body, such as the brain, and if so, symptoms such as seizures, or other signs of compromised organ function may be seen. This, however, is far less common than finding cysts in or attached to the liver, intestines or body cavity.

(Pictured at right: a group of infective cysts attached to the domestic rabbit's intestines.)

Wild eastern cottontails have occasionally been found carrying hundreds of these cysts in nearly every part of the body, resulting in a gaunt rabbit in ragged condition before they die. More usually, an infected rabbit carries the average number (6), but usually no more than up to 20 infective cysts. Usually the domestic rabbit manages fairly well despite the cysticerci, and it is uncommon that a diagnosis is made while the rabbit is alive.

Between 28% and 65% of all cottontails are infected with T. pisiformis, depending on species, location and age.

"Cysticercus pisiformis" - the condition of being infected with immature tapeworm cysts - is the extent of tapeworm infestation in rabbits. Tapeworms do not mature in rabbits. The immature tapeworms simply wait inside their cysts until a dog or coyote kills and consumes the rabbit, eating the cysts along with other rabbit parts.

Stage V of the tapeworm life cycle completes itself with the ingestion of the cysticercus by the primary host - a dog or other canid. The immature tapeworms finally mature into adult tapeworms. The canid begins shedding tapeworm eggs, and the cycle starts all over again....

The good news - T.pisiformis does not infect humans.

Treatment:
Mebendazole, 1 gm/kg of feed for 14 days (approx 50 mg/kg bodyweight per day), should kill both mature and immature tapeworm cysts of T.pisiformis. Withdrawal time is 48 hours. Please confer with your rabbit-savvy vet.

Prevent Reinfection:
To prevent reinfection, clean living spaces of all feces, especially dog feces, and prevent recontamination. If your rabbits are caged, consider discarding all hay, and purchasing fresh.

Tapeworm Life Cycle and Summary of Treatment:
When you recognize a tapeworm infestation:

• If you see something that looks like a fettucine noodle hanging out of the backside of your dog, you're probably looking at an adult tapeworm. There is, therefore, a possibility that one or more of your rabbits has become an intermediate host. (Can't assume, however - a cottontail could have been the source of your dog's unwelcome guest.)
  
  
• Treat your rabbits and dogs with de-worming medication when an infestation is recognized (you'll need vet assistance)
  
  
• If you butcher rabbits for meat, look for cysticerci in the guts of EVERY rabbit butchered. Even if a cysticercus is not found, check the liver for scarring, telltale signs of the larval stage within the liver
  
  
• Working sheepdogs should be regularly de-wormed as sheep can also host tapeworms
  
  
• Practice good hand-washing before and after handling dogs, rabbits and feeding rabbits
  
  
• Don’t feed the rabbit guts to your dog or cat
  
  
• Meat from infected rabbits is not necessarily condemned, however in heavily infested carcasses with many, or older, cheesy cysts, the carcass is condemned.
  
  
• Carefully inspect the raw meat you feed your dogs and cats. During a known infestation, freeze the meat and then thaw and feed to your carnivores
  
  
• According to the CDC, "Freezing (23° F, –5°C) meat for 4 or more days will kill cysticerci." The Mayo Clinic suggests freezing for 12 hours is sufficient.
  
  
• Cooking meat to 150 degrees F will kill tapeworms, states the CDC. Cook meat thoroughly, per the NHS.

• Cysticercus fasciolaris is the cystic stage of Taenia taeniaeformis, the cat tapeworm
• T.pisiformis (dog tapeworm) is occasionally found in cats
• Coenurus serialis is the intermediate stage of Taenia serialis, a tapeworm of the dog and fox, and is almost always fatal to hares, rabbits and other related rodents. It is passed into the connective tissue of the lumbar muscles, hind leg muscles and rarely into the jaw muscles. Coenurus serialis may also occur accidentally in the brain and muscle tissue of humans.
• For treatments, please consult your rabbit-savvy veterinarian.

This Tapeworm Life Cycle page is specific to Cysticercus pisiformis - an infestation of the common dog tapeworm Taenia pisiformis.

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