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Diphyllobothrium spp. (Diphyllobothriasis): Pathogenesis and species - Parasitological diagnosis; Molecular identification of species

 

Information 16/08/24.

 

Diphyllobothriasis is a zoonosis transmitted by plerocercoids fish containing tapeworm larvae species (band - like worms) of the genus Diphillobothrium (Cestoda, family Diphyllobothriidea).

 

The life cycle of these helminths involves two intermediate hosts (one -copépodo- aquatic arthropod and fish). Aquatic arthropod ingested helminth eggs are eliminated with the faeces of definitive hosts where the adult worms (man or other mammal piscívoro or waterfowl). Human infection of humans, other mammals or birds that eat fish aquatic occurs when fish are eaten raw or undercooked (eg., Marinades), containing the plerocercoids larvae. In turn, the fish are infected when they eat aquatic crustaceans (copepods) ingesting helminth eggs and larva developed the procercoid.

 

This infection often goes unnoticed until the infected person removes proglótides (rings) of the tapeworm that have matured in your gut. When the infected person shows any symptoms are usually minor digestive problems (nausea, diarrhea or abdominal discomfort). When the infection is long - term patients may have megaloblastic anemia (pernicious anemia) Vitamin B12 deficiency. To avoid infection should be kept frozen fish that will be consumed without heating, at least 24 hours (1 to 7 days depending on the thickness of the fish) at -20 ° C or below. When be subjected to cooking temperature should be 55 ° C or more for at least 5 minutes.

 

In the epidemiological history of infected patients is the ingestion of raw or marinated fish. Ingestion of marinated salmon or other fish usually present. To establish a causal relationship to the ingestion of some raw or marinated fish must take into account the time of ingestion and the onset of the first symptoms is usually 2 to 6 weeks, ie time since ingest fish infected with larvae plerocercoids until the adult worm develops. In experimental studies argentea feeding gulls (herring gull) has shown that it can be 5 to 20 days.

 

Diphillobothrium latum has been the only species accepted for a long time as a human pathogen, causing diphyllobothriasis. Currently, other species such as Diphyllobotrium dendriticum, D. and D. nihonkaiense pacificum as species that can often be found infecting people allowed. Less common species are: D. cordatum, D. lanceolatum, D. ursi, D. alascense, D. dalliae, D. cameroni, D. hians, D. D. scoticum or stemmacephalum.

This infection had decreased in incidence, but travel, migration, international trade in fish, especially the new eating habits that have increased consumption of raw fish or marinades, has increased the incidence of number of cases and species of Diphillobothrium that may be infecting people. European countries such as Switzerland, France, Italy, Nordic, Spain, or others, have reported cases of infection distintass species Diphillobothrium latum.

Diagnosis of these infections is performed when the patient removes proglótides with feces, or the presence of deleted by helminths in stool by a method of concentration is investigated eggs. The eggs of these species are characterized by not being embryonated when excreted in the faeces and having a hardly visible operculum at one pole and a small bump on the opposite pole. To identify proglótides methods for making translucent and staining (lacto-acetic carmine) to observe the internal structures as its central rosette uterus required.

To differentiate the various species that can infect people, morphologic criteria are difficult to apply because they are based on differences in their scolex (apical binding region) and handles the uterus of the female reproductive system. For this reason, today, the species differentiation is performed by molecular methods based on differences in their DNA. Have been applied many methods genomic studies but the most currently used are tests PCR (polymerase chain reaction) with primers (primers) specific species, or by amplification of some genes encoding ribosomal RNA (5, 8S rRNA, 18S rRNA or regions iTS iTS 1 or 2 -Internal transcribed spacer-) and the gene encoding cytochrome c oxidase subunit 1 (cox1), followed by sequencing.

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