Introduction

Dipylidium caninum is a tapeworm that commonly infects dogs and cats. Transmitted by ingestion of an infected flea, D. caninum occasionally affects humans, especially children. D. caninum, therefore, is a serious concern for pet owners and parents.

Adult D. caninum: http://www.dpd.cdc.gov/DPDx/HTML/ImageLibrary/Dipylidium_il.htm

Parasitic Agent: Dipylidium caninum

Synonyms: Dog or cat tapeworm; double-pored dog tapeworm

Classification:

Kingdom: Animalia

Phylum: Platyhelminthes

Class: Cestoda

Order: Cyclophyllidea

Family: Hymenoleopididae

Genus: Dipylidium

Species: D. caninum

History of Discovery:

Dipylidium caninum has been a known parasite since the beginning days of the Linnaean classification system. A paper by Zschokke in 1903 cites a student of Linneus by the name of Dubois as the first reporter of D. caninum in 1751. An article by William Riley in Science Magazine in 1910 reveals that D. caninum had been known as a dog parasite for quite sometime, but rarely seen in humans. It seems that the first cases of D. caninum in humans were noted in 1903 with several cases in Europe and one in the U.S.

Morphology:

Mature proglottid: http://www.dpd.cdc.gov/DPDx/HTML/ImageLibrary/Dipylidium_il.htm

Dipylidium caninum is a tapeworm that is relatively small in its adult form (~15cm). It can, however, reach as long as 80cm. The four suckers of the scolex or head of D. caninum distinguishes it as a Cyclophyllidea cestode. The proglottids of D. caninum are longer than they are wide. A characteristic feature of these proglottids is that they contain two sets of male and female reproductive organs. They therefore demonstrate two genital pores that lead to their name as the “double-pored” tapeworm.

Within the gravid proglottids are egg packets. The number of eggs can range from 5 to 30. The larvae of D. caninum are known as cysticercoids because the scolex is enclosed in a fluid-filled cyst at this stage.

 

Life Cycle

Gravid proglottids containing egg packets are passed in the feces of an infected host. The egg packets are released from the proglottids that break apart. Dog or cat fleas, normally of the species Ctenocephalides, ingest these egg packets. The fleas act as an intermediate host because the oncospheres hatch from the eggs within these fleas and develop to become infectious larvae, cystercoids. D. caninum is transmitted by the ingestion of the flea that carries D. caninum in its infectious larval state. Inside the small intestine of the definite host, the larvae develop into adult worms. D. caninum hooks onto the intestinal lining of the small intestine with its scolex. Several worms can be within a host at one time. As hermaphrodites, D. caninum can self-mate. Proglottids break off and are passed in the feces. The proglottids can migrate from the anus to the exterior of the host where they contract and expand vigorously. This behavior may function to release the egg packets within the proglottids.

 

Human Infection

Clinical Presentation:

- Light infections of D. caninum often are asymptomatic.

- Infection, however, can still cause abdominal pain, diarrhea, and anal pruritus (itch) in some individuals.

Transmission: Fecal-oral transmission, more specifically ingestion of vector

Definite Hosts: Dogs, Cats, Humans

Reservoir: unknown

Vector: Fleas (Ctenocephalide species)

Incubation Period: approximately 20 days

Clinical example:

“A 6-month-old girl was reported by her parents to be passing small, white, ricelike bodies in her stool over a 3-month period. They sought advice from their general practitioner, who thought these bodies were vegetable seeds. The baby was otherwise asymptomatic, but the concerned mother decided to submit a sample of the stool for consultation with pathologists.”

Proglottids. Molina et al.

 

Diagnosis

Diagnostic Tests:

Examination of stool for characteristic proglottids (see Morphology) and eggs packets (less common).

Proglottids and egg packets: Molina et al.

Management and Therapy:

Praziquantel is very effective and is given in one dose of 5 to 10 mg/kg body weight.

Niclosamide is an alternative, but may cause abdominal cramps, diarrhea, and nausea and vomiting in a small number of patients. Only a single dose is need at the following dosage: 2.0g for adults, 1.5g for children weighing over 34 kg, and 1.0 g for children weighing between 11-34 kg.

 

Epidemiology

www.satprints.com

Distribution:

Because human infection is the result of ingestion of infected dog or cat fleas, it occurs more often in children who kiss or are licked by their infected pets.

Country Information:

Distribution is worldwide. Human infections have been reported in Europe, the Phillipines, China, Japan, Argentina, and the United States.

Public Health and Preventive Strategies:

Ways to prevent infection include controlling the fleas and de-worming of pet dogs and cats. Praziquantel and Niclosamide are available as injection for pets.

 

References

Textbooks:

John, David T. and William A. Petri, Jr. Markell and Voge’s Medical Parasitology. St. Louis, MO: Saunders Elsevier, 2006. Pages 210, 231-233, 235, 349.

Articles:

Molina CP, Ogburn J, Adegboyega P. Infection by Dipylidium caninum in an infant. Archives of Pathology & Laboratory Medicine. 2003 Mar; 127(3):e157-9.

Riley, William. Dipylidium Caninum in an American Child. Science. New Series, Vol. 31, No. 792 (Mar., 1910), pp. 349-350.

Websites (Also Useful Weblinks):

http://www.dpd.cdc.gov/DPDx/HTML/Dipylidium.htm

http://www.emedicine.com/med/topic573.htm

 

Contact Information

Kim Tran, Class of 2007, kim.tran@stanford.edu

Stanford University

Parasites & Pestilence: Infectious Public Health Challenges

Professor D. Scott Smith, ssmith@stanford.edu