The cysticercosis is a parasitic disease caused by young larvae of several species of tapeworms of the genus Taenia (commonly referred to as "tapeworms") that have specific hosts.
In humans, cysticercosis is caused by the larvae of the flatworm Taenia solium after accidentally ingesting their eggs. These eggs attach to skeletal muscles, the central nervous system, both the brain and spinal cord, and other tissues, where the larvae develop. Cysticercosis that affects the central nervous system is called neurocysticercosis.
MRI of the brain of a patient infected with Taenia solium cysticerci
In the brain, the larvae encyst and calcify, forming structures or cysts known as "cysticerci" and the symptoms will depend on the location of these structures. This implies that the symptoms are very diverse, ranging from localized pain to the appearance of seizures.
The disease in humans is developed by the consumption of food or water contaminated with human feces that contain the eggs of Taenia solium.
The life cycle of these parasites includes an intermediate host where the larvae develop and a definitive host where the tapeworm develops in its adult form. In the case of human cysticercosis, man is the intermediate host.
Symptoms
Cysticerci can be located in many organs and body systems and, depending on their location, symptoms will be generated.
Outside the central nervous system, cysts can reach the subcutaneous tissue, preferably the chest and back. In skeletal muscles the preference is usually on the thighs of both legs. They can also reach the eye, liver, and kidneys.
In the thighs and subcutaneous tissue, cysts appear as small, very fine and soft lumps with a rubbery consistency. However, in these locations they do not cause major discomfort.
In the eye, liver and kidneys, the symptoms will depend on the number of cysts and, in the eye, on their location. The corresponding symptoms appear because the presence of cysts can cause failure in the function of these organs.
Neurocysticercosis can present as severe and constant headaches, partial or general seizures, disorientation, memory loss, or even death. It can present as meningitis or cerebral edema.
When cysticerci are located in the spinal cord, they can cause pain or local motor and sensory disorders in different areas, depending on the affected area.
In patients with seizures who come from rural areas, especially in countries with poor or scarce sanitary measures, these parasitic diseases should always be ruled out as the cause of seizures.
Characteristics of the parasite
Cysticerci are clusters of cestode larvae, which are long, flat parasitic worms that possess a linear series of reproductive organs called proglottids. Each proglottid is separated from another at its upper and lower end by a groove.
On the surface of the parasite there is a kind of very fine microvilli that serve to absorb nutrients, since they do not have a digestive tract. These parasites have an attachment organ called the scolex, with suction cups and spiny tentacles or attachment hooks.
All cestodes require at least two hosts and the adult parasite or tapeworm develops in the intestines of vertebrate animals. Each proglottid has male and female sex organs and can be self-fertilized or there can be cross-fertilization.
The embryo forms in the uterus from the proglottid and can be expelled through the uterine pore or by detachment of the terminal proglottid.
Life cycle
Feces with eggs or mature proglottids contaminate fields and waters and, when consumed by a host, the eggs hatch.
When the eggs hatch in the host's intestine, the larvae are released. These larvae have hooks with which they pierce the intestine and enter the bloodstream or lymphatic circulation.
It is from the circulation that they finally reach the muscles, where they become juvenile larvae.
The larvae encyst and transform into vesicular worms called juvenile larvae or cysticerci. Cysticerci already have an invaginated scolex and are encapsulated; this is what causes cysticercosis.
When infected meat is ingested by an appropriate host, the cyst capsule dissolves, the scolex exits and attaches to the intestine and begins to produce proglottids. The adult worm in man can measure up to 10 meters in length (encompassed by successive proglottids).
Causes
The parasite Taenia saginata or Cysticercus bovis is typical of bovines, that is, it causes cysticercosis in cattle. Cysticercus cellulosae or C. racemosus is the larval form of Taenia solium and is the one that affects apes and humans.
The species Taenia hydatigena, whose cysticerci are known as Cysticercus tenuicollis, infects dogs, cattle, pigs and sheep.
Taenia taeniformis, in its adult form, infects cats and infects the liver of rats. However, man is an intermediate host for tapeworms that affect pigs and cattle and become infected by eating undercooked contaminated meat.
In human cysticercosis, infection can occur through food or water contaminated with feces from an infected man. However, self-infection can occur in people with taeniasis.
An infected man eliminates significant amounts of eggs with the feces, however, the proglottids can escape through the anus without defecation and contaminate sheets and clothing. The lack of proper disposal of excreta or its use as compost spreads the disease.
Diagnosis
The diagnosis of human cysticercosis initially requires an interrogation regarding the patient's habits, their habitat or recent trips to rural areas or countries where there is a high prevalence of this type of disease.
For neurocysticercosis, the diagnostic suspicion is based on observation of plain radiographs showing calcifications in the thighs and brain.
Currently, the use of computerized axial tomography (CT) for diagnosis and control is very widespread, especially in cases of neurocysticercosis.
Histological study of accessible cysts confirms the diagnosis. The most widespread diagnostic and monitoring techniques involve the use of CT images to define lesions and observe remission after treatment.
The diagnosis of taeniasis (presence of eggs or mature proglottids in the stool) is made by a simple stool examination.
Treatment
The treatment of cysticercosis consists, on the one hand, in alleviating the symptoms, which may include surgery if necessary. Second, the use of drugs to eliminate cysticerci and tapeworms, in the case of patients suffering from both types of infection.
In the 90s, the use of praziquantel was reported at 50 mg per kg of body weight daily for a period of 15 days, demonstrating the elimination of 60% of cysticerci from the brain parenchyma in a period of three months.
Currently, the combination of the drugs albendazole and praziquantel is used. Praziquantel is used for the intestinal form of Taenia solium and the combination of albendazole and praziquantel for cysticercosis.
Prior to treatment with these parasiticides, a treatment with steroids as anti-inflammatories is usually given to minimize the brain inflammatory process that develops due to the death of the parasites.
References
- Del Brutto, OH (1995). Medical treatment of cysticercosis-effective. Archives of neurology, 52 (1), 102-104.
- Garcia, HH, & Del Brutto, OH (2000). Taenia solium cysticercosis. Infectious disease clinics of North America, 14 (1), 97-119
- Goodman, LS (1996). Goodman and Gilman's the pharmacological basis of therapeutics (Vol. 1549). New York: McGraw-Hill.
- Hickman, CP, Roberts, LS, Larson, A., Ober, WC, & Garrison, C. (2001). Integrated principles of zoology (Vol. 15). New York: McGraw-Hill.
- Brusca, RC, & Brusca, GJ (2003). Invertebrates (No. QL 362. B78 2003). Basingstoke.