Platyhelminthes: Taenia, Morphology, Life Cycle, and Impact
Platyhelminthes
Platyhelminthes are flat, elongated worms. They are invertebrates and hermaphrodites. They inhabit marine environments, land, and rivers. They have no respiratory or circulatory system. They need various hosts to reproduce, some for the larval stage and some for the adult stage. They are classified into: Trematoda, Cestoda, Turbellaria, and Monogenea.
Taenia: Morphology
Kingdom: Animalia; Class: Cestoda; Order: Cyclophyllidea; Family: Taeniidae; Genus: Taenia; Species: saginata, solium.
Taenia Characteristics and Life Cycle
Their adult forms develop in the human intestine, which acts as the only definitive host. The larval stages, or cysticerci, develop in the tissues of animals (pigs, feral pigs, and cattle) or humans. Their length varies according to species, from 3 mm to more than 10 m. Like other cestodes, they lack a digestive tract. Their body is segmented, and they are gastrointestinal parasites of vertebrates and invertebrates. They are hermaphrodites. The parasite genus Taenia is a zoonotic disease whose prevalence rates vary depending on various socio-economic and cultural factors.
Reservoir: Humans (adult tapeworm). In pigs: larva of T. solium; in veal: larva of T. saginata. It produces intestinal taeniasis (T. saginata) and intestinal taeniasis and cysticercosis (T. solium).
Transmission mechanisms: The route of elimination is the anus, and the means of disposal is feces. The agent of infection in the intermediate host is: Taenia solium in pork and Taenia saginata in cattle. Pigs and cattle become infected by eating grass and/or water contaminated with the feces of people infected with the parasite.
Taenia solium Life Cycle
Eggs are spread in the environment through the feces of infected people. These eggs contain an embryo that is released when ingested by the intermediate host (in this case, pigs and wild boars). The embryo invades the musculature, spreading through the blood after passing through the intestine. There, it grows into the Cysticercus cellulosae phase, which is a vesicle measuring about 5 to 20 mm. Within this vesicle is the larval form of the parasite. When ingested by humans through the consumption of raw or undercooked meat, it is set in the intestine where it generates the adult hermaphrodite, completing the cycle.
Taenia saginata Life Cycle
The life cycle is similar to T. solium, but here, the intermediate hosts are cattle, and it produces no human cysticercosis. Hence the importance of differential diagnosis between the two species. Humans acquire the infection by eating raw or undercooked beef. In this case, the emission of the rings tends to occur one by one and not necessarily accompanied by the feces.
Epidemiology
Prevalent in both urban and rural areas with poor sanitation and hygiene, ignorance, and poverty. There is high prevalence in China and Slavic nations. In Chile, infection with T. saginata is more frequent than with T. solium, with a ratio of 8 to 10 cases to one.
Symptoms
They are characterized mainly by producing a multiform, low-gravity symptom complex. Symptoms appear approximately 5 to 12 weeks after ingestion of cysticerci. General symptoms include appetite disorders (bulimia, anorexia, increased appetite), abdominal pain, nausea, constipation, or diarrhea, irritability, and change of character. The hallmark of these parasites is the spontaneous expulsion of proglottids, which occurs in 95% of cases.
Diagnosis
Diagnosis begins with the observation of chains of proglottids in the stool or attached to clothing. The specific diagnosis must be made by microscopic observation of eggs by coproparasitoscopic diagnosis.
Treatment and Prevention
Pumpkin seeds, as a vermifuge, were among the first remedies against taeniasis. Treatment for T. solium and T. saginata is the same, and the most widely used drugs are albendazole and praziquantel.
Prevention:
- Avoid ingestion of raw or undercooked beef or pork.
- Wash hands after handling meat or pork.
- Wash hands after defecation.
- People who harbor the parasite should be treated immediately.