This child was diagnosed with a Diphyllobothriasis infection or “Fish Tapeworm” infection.
Diphyllobothriasis – the causative organism described
The Diphyllobothrium latum (D. latum) is a Helminth worm belonging to the Cestodes or tapeworms group. It is also called Dibothriocephalus latus and it belongs to the family Diphyllobothriidae. The Diphyllobothriidae contain various species that infect other animals. D. latum and D. nihonkaiense are the most common to infect humans. D. nihonkaiense is most commonly seen in Japan but a recent infection in the state of Washington was identified as D. nihonkaiense. In contrast, D. latum is found in a more expansive geographic area. This includes Northern Europe, Russia, North America, South America, and Central Europe. Overall the circumboreal distribution of the tapeworm can be attributed to various factors including globalization, human migration, and aquaculture. The Cestodes are called tapeworms due to their flat segmented ribbon like form. There are three subgroups that make up the Helminth group, the Cestodes, Trematodes, and Nematodes. In comparison, due to their form, the Trematodes are called flatworms and the Nematodes are called roundworms.
D. latum is the largest of the Cestodes. It can reach a length of 33 feet in the small intestine. Besides their large size they can also exist in the host for 20 years or longer. In many cases the infection is asymptomatic. But when symptoms occur, they can include abdominal discomfort. Other symptoms are diarrhea, vomiting, and weight loss. Megaloblastic anemia due to vitamin B12 deficiency may also occur. There are complications that can occur which include intestinal obstruction and/or gall bladder disease.
How Infections Are Acquired
Infections occur from consuming rare or under cooked fish infected with the tapeworm larvae. Different species of Diphyllobothriidae. And though many have a definitive host other then humans, these can infect humans as well. These other species also infect different fish. It is crucial to consider the clinical history of the patient. Especially when considering that fish can be exported for consumption from various parts of the world.
Infections are best prevented by avoiding the consumption of raw fish or under cooked fish. Fish should be cooked to a temperature of 63 degrees centigrade. Alternatively, it should be kept frozen at a temperature of -20 degrees centigrade for 7 days in total.
The Epidemiology of Diphyllobothriasis
In the United States D. latum is the most likely cause of fish tapeworm infection. Alaska and the Great Lakes region are most likely to have these infections. Salmon is most likely to be the source. Other fish such as pike, trout, whitefish, and other less popular species may also be sources.
The first case in the United States that was detected was in 1906. It was considered a reportable disease to the CDC until 1982. The incidences of the disease have decreased significantly. However, the globalization of food presents the possibility of Diphylobothriasis increasing. Especially concerning is the unrelenting pressure to ship fish products unfrozen or fresh. A necessity to be competitive in the global fish market.
Case Study Discussion
In this case study, further questioning revealed that the child attended a camping trip some months prior. At the camping trip the group consumed freshly caught fish that was campfire cooked. The findings in the ova & parasite examination suggest a parasitic worm infection. The history of consuming possibly undercooked fish was taken into account. The geographical location (Great Lakes region of the United States) was also considered. The eggs seen in the ova & parasite examination have characteristics of D. latum. These characteristics include a prominent operculum at one end. They have an oval to ellipsoid shape and a specific size. There is a small knob at the abopercular end and a thin shell. Diphylobothriasis is the diagnosis.
The symptoms in the child and blood test results are within the spectrum of Diphylobothriasis. The megaloblastic anemia is a result of the parasite consuming vitamin B12 and preventing the host from absorbing it. This results in a macrocytic red cell anemia, low platelet count, and at times a low white cell count. All evident in the Childs blood test results.
The importance of obtaining a complete and accurate clinical history is evident in this case study.
Treatment
The treatment of choice for Diphyllobothriasis is Praziquantel which can be done on an outpatient basis with a single dose. The drug effectively interferes with calcium metabolism in the worm resulting in a flaccid paralysis of the worm. The worm is unable to remain attached to the intestinal wall. This results in the worm being able to be expelled from the host. Other drugs that can be used are albendazole and nitazoxanide.
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References:
DIPHYLLOBOTHRIUM LATUM INFESTATION ON THE EASTERN SEABOARD: TWENTY-ONE CASES FROM NEW YORK MILTON PLOTZ, M.D. Author Affiliations JAMA. 1932;98(4):312-314. doi:10.1001/jama.1932.02730300042011
CDC – https://www.cdc.gov/diphyllobothrium/about/index.html
Epidemiology of Diphyllobothrium nihonkaiense Diphyllobothriasis, Japan, 2001-2016 Hiroshi Ikuno 1,2,✉, Shinkichi Akao 1,2, Hiroshi Yamasaki 1,2 Emerg Infect Dis. 2018 Aug;24(8):1428–1434. doi: 10.3201/eid2408.171454
Update on the Human Broad Tapeworm (Genus Diphyllobothrium), Including Clinical Relevance Tomáš Scholz 1,*, Hector H Garcia 2, Roman Kuchta 1, Barbara Wicht 3,4Clin Microbiol Rev. 2009 Jan;22(1):146–160. doi: 10.1128/CMR.00033-08
Disclaimer: The information contained in this case study is to be used only as a case study example for teaching purposes. The information in the case study is both factual and fictional. Opinions formulated by the author are intended to stimulate discussion.