BEWARE OF THIS PARASITE!


*Image of courtesy of
www.emedicine.com

Name: Dipylidiasis (DIE-pih-lih-DIE-uh-sis)
AKA: Dog Tapeworm, Double-pored Tapeworm
Length: 10-70 cm
Diameter: 2-3 mm
Target: children under eight
Accomplices: Fleas, Lice, Dogs, Cats
Location: worldwide

For more information about this parasite and how to protect yourself, explore this website.



Introduction

Welcome to the Dipylidiasis paraSite for Human Biology 103. In this website you will find all the information you need on this parasite, including the morphology and life cycle. More importantly, you will find information on the interaction between this parasite and humans. Finally, the Websites and References section will provide you with additional sources to expand your knowledge of this parasite.

Dipylidium caninum (DIE-pih-LID-ee-um k-nine-um) is the common tapeworm of cats and dogs. It is classified with other tapeworms in the class of Cestoda and more specifically in the family Dilepididae. It is also commonly known as the double-pored tapeworm. It was first discovered by Linnaeus in 1758 to infect humans.

Parasite Information


Morphology

Adult: The adult worm is hermaphroditic and can reach an average length of 30cm (10-70cm) and 2-3mm in diameter. The parasite has a conical, retractable rostellum on the scolex with an average of 4-6 rows of hooks, although they may range from one to eight rows. These hooks function in securing the tapeworm into the wall of the small intestine. Additionally, four suckers are located on the scolex to feed. This tapeworm is easily distinguishable from others by its characteristic proglottids (tapeworm segments), which has two sets of reproductive organs located on opposite ends.

*Image of adult tapeworm courtesy of www.emedicine.com *Image of tapeworm scolex courtesy of cal.vet.upenn.edu
*Image of proglottid courtesy of www.emedicine.com *Image of carmine stained proglottid courtesy of www.emedicine.com


Eggs: The eggs are released from gravid proglottid in packs of 5-30 eggs. Each gravid proglottid may contain up to 50 or more egg packets. The egg packets form after sexual reproduction as the uterine lining encapsulates the eggs.

*Image of egg courtesy of www.emedicine.com *Image of egg packet courtesy of www.emedicine.com *Image of egg packet courtesy of www.emedicine.com

Larva: The cysticercoid larvae develop within the stomach of the larval intermediate hosts (dog and cat fleas). The cysticercoid larvae become infective when the intermediate hosts mature into adults and reside in the body cavity of the flea.


Transmission

Transmission occurs by ingestion of fleas infected with larval cysticercoids.


*Image of dog ingesting flea courtesy of www.marvistavet.com

Intermediate Host

Fleas of the Pulex and Ctenocephalides species (C. canis and C. felis respectively) are the most common intermediate hosts. Occasionally, the dog louse (Trichodectes canis) will also act as an intermediate host.


*Image of a flea courtesy of www.ipmalmanac.com

Reservoir

There is no reservoir for this parasite.


Incubation Period

It takes approximately 10-25 days for the larva to mature into adulthood within the small intestine. As an adult, the lifespan is approximately one year.


Life Cycle


*Image of life cycle courtesy of www.cdc.gov

The life cycle begins when egg packets within the proglottid are released into the environment. Larval dog and cat fleas then ingest the egg packets. Inside the stomach of the larval fleas, oncospheres develop and hatch from the eggs where they penetrate the stomach wall of the flea larvae. Cysticercoid larvae of the tapeworm then develop within the body cavity of the larval flea. The infected larval flea develops normally to an adult flea, which harbors the infective larval cysticercoid. Transmission of the tapeworm to dogs and cats occurs when they ingest an infected flea. The infective cysticercoid develops into adult form in the small intestine of the hose, where it attaches its scolex to the intestinal wall within a month. Proglottid segments of the tapeworm reproduce with their two sets of reproductive organs and produce multiple egg packets. The gravid proglottids detach from the adult tapeworm and either migrate out of the anus or pass in the stools. Humans are accidental hosts and infection is accidentally acquired when they ingest infected fleas. The source of fleas is usually from their pets and infection occurs when dogs or cats chew on fleas and then lick a human's face. In the human the cysticercoid develops into adult form in the small intestine, where the scolex attaches. As with dog and cat infections, the tapeworm reproduces to form gravid proglottids with egg packets that pass in the feces or migrate out of the anus.

Dipylidiasis and Humans


Epidemiology

Dipylidiasis occurs most in children under eight years of age. They are most frequently infected when licked by a dog or cat with infected fleas. A high percentage of children infected are under six months of age. This disease occurs throughout the world. There have been documented cases in Africa, Argentina, Australia, Chile, China, Europe, Guatemala, India, Japan, Philippines, and the United States. In the United States, very few cases have been reported, only six in the past twenty years.

*Image of dog and child interaction courtesy of www.kateconnick.com*Image of dog and human interaction courtesy of www.funpages.com


Symptoms

Most infections in humans are asymptomatic. However, as worm burden increases, symptoms of Dipylidiasis may develop or intensify. Most symptoms are intestinal disturbances, such as abdominal pain, loss of appetite, pruritus or rashes from allergic reaction to the tapeworm, perianal itch, and intestinal obstruction (very rare). Worm burden is directly related to the number of infective cysticercoid larva ingested, since the worms do not multiply within the host.


Diagnostics

This tapeworm can be characterized by proglottids and/or egg packets in feces. Individual eggs in feces are rare and difficult to detect. Proglottids may resemble grains of rice in the feces, or as a yellowish object attached to perianal hairs. There are no blood tests available.


Treatment

Treatment is simple with these two recommended drugs:

DrugNiclosamide (Nicloside)Praziquantel (Biltricide)
Administeredonce orallyonce orally
Adult Dosage2g5-10mg per kg of patient weight
Children Over Four Dosage1.5mguse adult dosage
Children Under Four Dosage1gnot established


Management

Examine stool for proglottids or egg packets one and three months after treatment. A second treatment of medication is usually unnecessary.


Prevention

The best way to prevent Dipylidiasis in humans and in pets is through control of fleas. Flea collars, medication, and powders are excellent ways to prevent flea infestation of pets. Aerosol insecticides for large areas are also effective in controlling flea populations. Furthermore, inspect pets for possible infection. Check the pets' stools for proglottids and/or egg packets. Also, check whether there are proglottids are moving out of the anus or attached to the anal hairs. If you notice that your pet has lost weight, monitor the pet for other signs suggesting it may have a tapeworm infection. If pets are infected, take then to the veterinarian for a treatment of Praziquantel. Since children are most likely to become infected, do not allow children to play in areas soiled with animal feces, or with animals that have fleas. Finally, as always, practice good hygiene such as washing hands often.


*Image of proglottids attached to perianal hair courtesy of www.marvistavet.com

Public Health Interventions/Strategies

No public health intervention has been proposed, but people with pets are encouraged by veterinarians to control flea infestation of pets. In the United States pet flea control is very common, but in other countries it is much more difficult and less common.


Medical Case Study

This medical case study is courtesy of Allen Press Online Archives of Pathology and Laboratory Medicine. This 2002 case is the first reported case of Dipylidiasis since 1992.

A six month old girl in Texas was reported to have been passing small rice-like things in her stool. For three months she had been passing these things without any apparent symptoms. The family pediatrician characterized these white bodies as passed vegetable seeds. Unconvinced, the mother brought a stool sample to a pathology lab.

The white rice-like bodies were Dipylidium Caninum gravid proglottids. When examined under a microscope, the stained tissue segments showed egg packets (8-15 eggs) and the characteristic double pore. This was adequate pathologic findings to diagnose the little girl with Dipylidiasis.

The little girl was given a dose of Praziquantel. She completely recovered without any complications. The family had no pets, so the source of infection was thought to be the pet dog from her daycare center.


Websites and References for Dipylidiasis and Other Parasites

Websites

Family Practice Notebook Dipylidiasis Information Page or the Family Practice Notebook Homepage

EMedicine Dipylidiasis Information Page or the EMedicine Homepage

CDC Dipylidiasis Information Page or the CDC Homepage

Mar Vista Animal Medical Center Tapeworm Information Page or the Mar Vista Animal Medical Center Homepage

Allen Press Online Archives of Pathology and Laboratory Medicine Homepage

References

1.) Markell, Edward K., David T. John and Wojciech A. Krotoski, eds. Medical Parasitology. 8th ed. Philadelphia: Saunders, 1999.

2.) Bogitsh, Burton J., and Thomas C. Cheng, eds. Human Parasitology. 2nd ed. San Diego: Academic Press, 1998.

3.) Marquardt, William C., Richard S. Demaree, and Robert S. Grieve, eds. Parasitology and Vector Biology. 2nd ed. San Diego: Harcourt Academic Press, 2000.

4.) Mehlhorn, Heinz, ed. Encyclopedic Reference of Parasitology: Biology, Structure, and Function. 2nd ed. 2 vol. New York: Springer, 2000.
5.) Wilson, Walter R., and Merle A. Sande, eds. Current Diagnosis and Treatment in Infectious Diseases. San Francisco: Lange Medical Books, 2001.

6.) Gorbach, Sherwood L., John G. Bartlett and Neil R. Blacklow, eds. Infectious Diseases. 2nd ed. Philadelphia: W.B. Saunders Company, 1998.

7.) Mandell, Gerald L., John E. Bennett and Raphael Dolin, eds. Principles and Practice of Infectious Diseases. 5th ed. Philadelphia: Churchill Livingstone, 2000.
8.) Ash, Lawrence R., and Thomas C. Oritel, eds. Atlas of Human Parasitology. 4th ed. Chicago: ASCP, 1997.

9.) Sun, Tsieh, ed. Parasitic Disorders: Pathology, Diagnosis, and Management. 2nd ed. Philadelphia: Williams and Wilkins, 1999.


Website Creator: Mary Sun
Course Number: Human Biology 103
Course Title: Parasites and Pestilence: Infectious Public Health Challenges
Professor: Dr. Scott Smith, MD, MSc., DTM&H
University: Stanford University
Date: 2003 Spring Quarter
Questions? Contact Mary!