Taenia solium: what does having the tapeworm mean?

by Giuseppe Scarlata, Antonino Napoleone | July 29, 2021.

The cuisine and culinary traditions are intrinsic and fundamental aspects of a society that best characterize the culture and lifestyle of a population. If we talk about food and good cuisine, the link with the Italian culinary tradition is so obvious that it has become a stereotype known all over the world: Italians are food lovers. During the lockdown of the previous months, it had become a trend to take pictures with family members in the kitchen trying to emulate the recipes of the greatest chefs, and there was a huge increase in the number of home-made preserves and food packages sent to family members away from home (read more: preparing and shipping home-made food packages). 

Food is clearly a source of conviviality and is known to have a positive influence on well-being and physical and mental health, as long as it is good, well preserved and properly cooked. In fact, food if not correctly processed can be the ideal habitat for the proliferation of pathogenic species, most of them visible only by using a microscope in the lab.  In colloquial language, a peculiar expression is used to describe a huge, almost uncontrolled appetite, i.e. the presence of the famous tapeworm is suspected. But when it comes to nutrition and infections, or in this case infestations, it is not just a way of saying, but it refers to a real parasite, large enough to be visible even with the naked eye! What does it mean to have a tapeworm? Which diseases are associated with it? What type of treatment is recommended and how can the risk of parasite infestation be prevented?  

Taenia solium life cycle 

Taenia solium is a parasite of the cestode class, which usually infests the intestines of the host organism. It is particularly long, measuring between 2 and 7 meters in length, and can even be seen with the naked eye, without any need for a microscope. It has a uniquely shaped head called scolex with a double crown of hooks and four suckers that allow it to adhere to the host’s intestinal wall (Figure 1).

The pig is the intermediate host of Taenia solium, which then reaches humans at the end of its biological cycle (Figure 2), where it is responsible for diseases such as taeniasis and cysticercosis. As the pathogen is closely linked to the consumption of pork meat, it is not observed in Islamic countries, while it is endemic in Central and South America and India. In Italy, there are only a few cases, most of which are confined to the South. 

Associated diseases, diagnosis and treatment 

Initially, tapeworm infestation presents with mild symptoms including an excessive appetite associated with caloric deficiency, fatigue, diarrhoea, abdominal pain, nausea and vomiting. Two diseases associated with Taenia solium infestation are characterised by more severe symptoms: 

• Taeniasis: the cause is associated with the consumption of raw or undercooked pork meat. Often the infestation is asymptomatic or paucisymptomatic, but in general the symptoms are associated with abdominal pain, stomach aches and loss of weight despite persistent appetite. This explains the common association between eating a lot and not gaining weight, which is underlined by the phrase: “do you have a tapeworm?”. The most visible sign of taeniasis is the active passage of proglottids (tapeworm segments) through the anus and into the faeces, but, in rare cases, the segments are deposited in the appendix or in the bile and pancreatic ducts. The diagnosis is made in the laboratory by parasitological examination of faeces collected on three different days to look for Taenia eggs, which can be detected 2-3 months after infection. Praziquantel at a dosage of 5-10mg/kg orally is the drug of choice for the treatment of taeniasis, followed by a new parasitological examination of the faeces 1-3 months after the end of treatment to indicate its effectiveness. 

• Cysticercosis: a disease associated with the development of larval cysts (cysticerciae) in the brain (neurocysticercosis), muscles and tissues after ingestion of raw or undercooked pork. The infestation is generally asymptomatic in the muscles, but it is much more severe at the neurological level, causing headaches, convulsions, difficulty in balancing and excess fluid in the brain (hydrocephalus). Symptoms appear months to years after the infestation has occurred, either when the cysts die, triggering intraparenchymal inflammatory processes, or when they are localised outside the brain parenchyma, where lesions occur at the ventricular level as they tend to grow, occupying the surrounding spaces and causing massive inflammatory processes.  The diagnosis is generally based on serological tests and imaging techniques (Figure 3). The aforementioned Praziquantel is used for the treatment, but several studies support the efficacy of Albendazole at a dosage of 15mg/kg/day for 15 days in eliminating living cysticerci, which is also more effective in prolonged treatment (up to 30 days) in extraparenchymal forms. 

Conclusions 

The occurrence of suspicious symptoms such as those listed above should draw attention to the fact that a medical examination is needed as soon as possible to confirm the diagnosis of tapeworm. The diagnosis is usually confirmed in specialised laboratories by coproparasitological test on faecal samples, where the presence or absence of Taenia solium eggs is detected. The best way to prevent such unpleasant encounters while eating, and to avoid the risk of having a host lurking in your own intestines for months or even years, is to eat well-cooked meat. Deep freezing is also effective against the risk of tapeworm infestation. In fact, it has been shown that eggs can survive for days if the meat is stored in the refrigerator at +4°C, while they are quickly eliminated if the meat is frozen at sub-zero temperatures (four days at -5°C and less than a day at -24°C). In this case, too, prevention is definitely the safest way to go. In fact, even in the kitchen, as in everyday life, small precautions can make a big difference. After all, some dishes are so delicious that you don’t want to share them with anyone else, not even with your own tapeworm.   

References 

1. https://www.cdc.gov/parasites/taeniasis/index.html 
2. Gonzales I, Rivera JT, Garcia HH; Cysticercosis Working Group in Peru. Pathogenesis of Taenia solium taeniasis and cysticercosis. Parasite Immunol. 2016;38(3):136-146. doi:10.1111/pim.12307 
3. Carpio A, Kelvin EA, Bagiella E, et al. Effects of albendazole treatment on neurocysticercosis: a randomised controlled trial. J Neurol Neurosurg Psychiatry. 2008;79(9):1050-1055. doi:10.1136/jnnp.2008.144899 
4. Sotelo J, Rosas N, Palencia G. Freezing of Infested Pork Muscle Kills Cysticerci. JAMA. 1986;256(7):893–894. doi:10.1001/jama.1986.03380070099027 
5. Fan PC, Ma YX, Kuo CH, Chung WC. Survival of Taenia solium cysticerci in carcasses of pigs kept at 4 C. J Parasitol. 1998 Feb;84(1):174-5. PMID: 9488360.