NEUROCYSTICERCOSIS (NCC): AN EMERGING ZOONOSES IN INDIA
Cysticercosis, popularly known as Tapeworm [Taenia solium] infection, is a very common disease where the patient would have consumed food or water infested with tapeworm eggs or larvae. These grow into adult tapeworms that cause an invasive infection by forming cysts in body tissues and organs outside the intestines or an intestinal infection by growing right inside the intestines.
These adult tapeworms have a head, neck and a series of segments called proglottids. A person with intestinal infection will have the tapeworm head stuck to the intestinal wall where the proglottids grow and multiply more eggs. At a given time, such tapeworms can live up to 30 years in the host.
The clinical conditions caused by Taenia solium are classified as either Cysticercosis (cysts in various tissues including the brain) or Taeniasis (intestinal tapeworm infection).
Taeniasis is usually mild, though persistent tapeworm infection can result in serious complications.
Cysticercosis is originates from the metacestode, (larval stage of Taenia solium), the pork tapeworm.
Neurocysticercosis refers to CNS infection with T solium. Neurocysticercosis is further classified into parenchymal and extraparenchymal disease. Parenchymal disease is distinguished by existence of cysticerci within the brain parenchyma. Extraparenchymal disease develops when cysticerci progress to the CSF of the ventricles, cisterns, and subarachnoid space or are seen within the eyes or spinal cord.
Taeniasis/cysticercosis——–
Symptoms
Usually, people with cysticercosis do not display any symptoms. It is actually the effects of the infection that lead people to go to doctors. Also, the type of infection and tapeworm, and the extent of infection and location determine most symptoms.
Intestinal Tapeworm Infection [Taeniasis]
Symptoms include
• Nausea
• No appetite
• Abdomen – twinges of discomfort
• Diarrhea
• Weakness
• Weight loss
• Poor absorption of nutrients from food
Taeniasis is an intestinal infection caused by 3 species of tapeworm: Taenia solium (pork tapeworm), Taenia saginata (beef tapeworm) and Taenia asiatica.
Humans can become infected with T. saginata or T. asiatica when they consume infected beef meat or pig liver tissue, respectively, which has not been adequately cooked, but taeniasis due to T. saginata or T. asiatica has no major impact on human health. Therefore, this fact sheet refers to the transmission and health impacts of T. solium only.
Infection with the T. solium tapeworm occurs when humans eat raw or undercooked, infected pork. Tapeworm eggs pass with the faeces and are infective for pigs. Infection in humans with the T. solium tapeworm causes few clinical symptoms. However as well as being infective for pigs, T. solium eggs may also infect humans if they are ingested, causing infection with the larval parasite in the tissues (human cysticercosis). This infection can result in devastating effects on human health. The larvae (cysticerci) may develop in the muscles, skin, eyes and the central nervous system. When cysts develop in the brain, the condition is referred to as neurocysticercosis. Symptoms include severe headache, blindness, convulsions, and epileptic seizures, and can be fatal. Neurocysticercosis is the most frequent preventable cause of epilepsy worldwide, and is estimated to cause 30% of all epilepsy cases in in countries where the parasite is endemic.
Cysticercosis mainly affects the health and livelihoods of subsistence farming communities in developing countries of Africa, Asia and Latin America. It also reduces the market value of pigs and cattle, and makes pork unsafe to eat. In 2015, the WHO Foodborne Disease Burden Epidemiology Reference Group identified T. solium as a leading cause of deaths from food-borne diseases, resulting in a considerable total of 2.8 million disability-adjusted life-years (DALYs). The total number of people suffering from neurocysticercosis, including symptomatic and asymptomatic cases, is estimated to be between 2.56–8.30 million, based on the range of epilepsy prevalence data available.
T. solium cysticercosis was added by WHO to the list of major Neglected Tropical Diseases (NTDs) in 2010 with NTD roadmap goals of making available a validated strategy for control and elimination of T. solium taeniasis/cysticercosis and those interventions to be scaled up in selected countries by 2020.
Symptoms
Taeniasis due to T. solium, T. saginata or T. asiatica is usually characterized by mild and non-specific symptoms. Abdominal pain, nausea, diarrhoea or constipation may arise when the tapeworms become fully developed in the intestine, approximately 8 weeks after ingestion of meat containing cysticerci.
These symptoms may continue until the tapeworm dies following treatment, otherwise it may live for a number of years. It is considered that untreated infections with T. solium tapeworms generally persist for 2–3 years.
In the case of cysticercosis due to T. solium, the incubation period prior to the appearance of clinical symptoms is variable, and infected people may remain asymptomatic for many years.
In some endemic regions (particularly in Asia), infected people may develop visible or palpable nodules (a small solid bump or node that can be detected by touch) beneath the skin (subcutaneous). Neurocysticercosis is associated with a variety of signs and symptoms depending on the number, size, stage, and location of the pathological changes as well as the host’s immune response, but can also be clinically asymptomatic. Symptoms may include chronic headaches, blindness, seizures (epilepsy if they are recurrent), hydrocephalus, meningitis, dementia, and symptoms caused by lesions occupying spaces of the central nervous system.
Treatment
Taenaisis can be treated with praziquantel (5-10 mg/kg, single-administration) or niclosamide (adults and children over 6 years: 2 g, single-administration after a light meal followed after 2 hours by a laxative; children aged 2–6 years: 1 g; children under 2 years: 500 mg).
In neurocysticercosis, since the destruction of cysts may lead to an inflammatory response, treatment of active disease may include long courses with praziquantel and/or albendazole, as well as supporting therapy with corticosteroids and/or anti-epileptic drugs, and possibly surgery. The dosage and the duration of treatment can vary greatly and depend mainly on the number, size, location and developmental stage of the cysts, their surrounding inflammatory edema, acuteness and severity of clinical symptoms or signs.
Prevention and control
To prevent, control and possibly eliminate T. solium, proper public health interventions with an approach spanning veterinary, human health and environmental sectors are required. Eight interventions for the control of T. solium can be used in different combinations designed on the basis of the context in the countries:
• treatment of taeniasis cases;
• intervention in pigs (vaccination plus anthelmintic treatment) together with strategic mass drug administration for taeniasis;
• health education, including hygiene and food safety;
• improved sanitation;
• improved pig husbandry; and
• improved meat inspection and processing of meat products.
Reliable epidemiological data on geographical distribution of T. solium taeniasis/cysticercosis in people and pigs is still scarce.
Appropriate surveillance mechanisms should enable new cases of human or porcine cysticercosis to be recorded in order to help identify communities at high risk and focus prevention and control measures in these areas.
Key facts about Taeniasis/cysticercosis
• Taeniasis is an intestinal infection caused by adult tapeworms.
• Three tapeworm species cause taeniasis in humans, Taenia solium, Taenia saginata and Taenia asiatica. Only T. solium causes major health problems.
• T. solium taeniasis is acquired by humans through the ingestion of tapeworm larval cysts (cysticerci) in undercooked and infected pork.
• Human tapeworm carriers excrete tapeworm eggs in their faeces and contaminate the environment when they defecate in open areas.
• Humans can also become infected with T. solium eggs by ingesting contaminated food or water or because of poor hygiene via the fecal-oral route.
• Ingested T. solium eggs develop to larvae (called cysticerci) in various organs of the human body. When they enter the central nervous system they can cause neurological symptoms (neurocysticercosis), including epileptic seizures.
• T. solium is the cause of 30% of epilepsy cases in many endemic areas where people and roaming pigs live in close proximity.
• More than 80% of the world’s 50 million people who are affected by epilepsy live in low and lower-middle income countries.
Neurocysticercosis (NCC) is the most common parasitic disease of the nervous system. It is the most common cause for seizures in India. NCC is the result of accidental ingestion of eggs of Taenia solium (ie, pork tapeworm), due to contamination of food with fecal material. The increase in the prevalence of NCC reflects poorly on the public health system of our country. It shows that the sewage disposal is poor and unhygienic food is consumed by people.
Neurocysticercosis (NCC) is the most common single cause of seizures/epilepsy in India and several other endemic countries throughout the world. It is also the most common parasitic disease of the brain caused by the cestode Taenia solium or pork tapeworm. The diagnosis of NCC and the tapeworm carrier (taeniasis) can be relatively inaccessible and expensive for most of the patients. In spite of the introduction of several new immunological tests, neuroimaging remains the main diagnostic test for NCC. The treatment of NCC is also mired in controversy although, there is emerging evidence that albendazole (a cysticidal drug) may be beneficial for patients by reducing the number of seizures and hastening the resolution of live cysts.
Neurocysticercosis is a preventable parasitic infection caused by larval cysts (enclosed sacs containing the immature stage of a parasite) of the pork tapeworm (Taenia solium). The larval cysts can infect various parts of the body causing a condition known as cysticercosis. Larval cysts in the brain cause a form of cysticercosis called neurocysticercosis which can lead to seizures. Neurocysticercosis, which affects the brain and is the most severe form of the disease, can be fatal. Neurocysticercosis is considered a Neglected Parasitic Infection, one of a group of diseases that results in significant illness among those who are infected and is often poorly understood by health care providers.
Cysticercosis caused by larval stage of the tapeworm Taenia solium, is a major public health problem, both in resource-poor as well as western developed countries. It is the single most common cause of epilepsy in the resource-poor endemic regions of the world including most of South and Central America, India, South-east Asia, China and sub-Saharan Africa.Humans are only definitive host of T. solium harbouring the adult tapeworm in the intestine (referred to as, taeniasis). Both humans and pigs act as intermediate hosts and harbour T. solium larvae in different internal organs (referred to as, cysticercosis) including the brain (referred to as, neurocysticercosis – NCC). Humans and pigs acquire cysticercosis through ingestion of eggs excreted in faeces of human carriers. Taenia solium infection is also being increasingly diagnosed in western, affluent countries because of human migration from, and travel to endemic areas. It is common in communities where pigs roam freely and people consume undercooked pork.3 Neurocysticercosis is central nervous system (CNS) infection with T. solium. It is perhaps the commonest parasitic infestation of the CNS, and has received attention in the last two decades because of the availability of MRI and CT scanning in the countries where cysticercosis is endemic.
Life- cycle of Taenia solium
The adult tapeworm resides in the small intestines of humans. Here, it is attached to the intestinal wall by suckers and hooks. A few gravid proglottids are detached from the distal end of the body everyday and passed in faeces. Each proglottid contains thousands of eggs, which are fully embryonated, infective, and resistant to adverse environments. Wandering pigs feed on human faeces containing T. solium eggs (Fig. 1). Once in the intestinal tract, the action of bile and pancreatic enzymes helps the eggs lose their coats, liberating oncospheres. These oncospheres cross the intestinal wall, enter the bloodstream, and are carried to the tissues of the host where embryos evolve to form larvae (also known as, cysticerci). In these circumstances, pigs become the intermediate hosts in the life cycle. Human consumption of inadequately cooked infected pork results in the transmission of viable cysticerci to the human small intestine, where, by the action of bile and digestive enzymes, the scolex of a cysticercus evaginates and attaches to the intestinal wall. Proglottids multiply and the parasite becomes a cestode that can be passed in the faeces as mature proglottids. Humans can also act as intermediate hosts for T. solium after ingestion of these eggs. In the given circumstances, human cysticercosis develops. The mechanisms by which eggs cross the intestinal wall and lodge in human tissues are the same as those in pigs. The two main sources from which humans contact cysticercosis are ingestion of food contaminated with taeniid eggs and the faeco-oral route in individuals harbouring the intestinal cestode. Once in the digestive tract, the eggs loose their coat due to action of gastric and pancreatic enzymes and liberate hexacanth embryos or oncospheres. Aided by their hooklets, onospheres cross the intestinal wall and local venules, enter the systemic circulation and are carried to different organs of the host. Here the oncospheres lose their hooklets, acquire a vesicular shape and evolve into cysticerci by gradual evagination of the protoscolex (invaginated scolex) over a period of several months. The life cycle is completed when undercooked pork infested with cysticerci is eaten. Humans may thus also become intermediate host and develop the larval stage of disease.
How people get neurocysticercosis:
A person gets neurocysticercosis by swallowing microscopic eggs passed in the feces of a person who has an intestinal pork tapeworm. For example, a person eats undercooked, infected pork and gets a tapeworm infection in the intestines. She passes tapeworm eggs in her feces. If she doesn’t wash her hands properly after using the bathroom, she may contaminate food or surfaces with feces containing these eggs. These eggs may be swallowed by another person if they eat contaminated food. Once inside the body, the eggs hatch and become larvae that find their way to the brain. These larvae cause neurocysticercosis.
Risk factors for acquiring neurocysticercosis:
People are at a higher risk for getting neurocysticercosis by swallowing parasite eggs if they:
• Have a pork tapeworm infection (this is called autoinfection)
• Live in a household with someone who has a pork tapeworm
• Eat food made by someone with a pork tapeworm infection
Neurocysticercosis is a preventable disease. Good hand washing practices and treating people infected with intestinal tapeworms could drastically reduce the number of new infections.
Diagnosis—————
The diagnosis is fairly simple and the doctor will ask for the following tests:
• Stool analysis Doctors and labs may ask for more than one stool sample to check for the presence of tapeworm eggs and the extent of infection.
• Blood sample Once the infection has invaded tissues, doctors will ask for a blood sample to check antibodies in the blood which definitely indicate presence of infection.
• Imaging tests A CT scan or MRI, X-ray or an Ultrasound is required to confirm invasive tapeworm infection and the presence of cysts.
Symptom—————–
NCC sometimes produces no clinical manifestation. This is due to variations in the locations of the lesions, the number of parasites, and the host’s immune response.
- Many patients are asymptomatic
- Some report nonspecific symptoms such as headache or dizziness.
- The onset of symptoms is usually acute, subacute to chronic. Patients may present with the following:
- Epilepsy
a. Epileptic seizures are the most common presentation
b. NCC is the leading cause of adult-onset epilepsy and is probably one of the most frequent causes of childhood epilepsy.
c. Seizures secondary to NCC may be generalized or partial (simple and complex partial seizures) may be associated with the presence of a single lesion. Irritation of focal cortical tissue by one of the lesions most probably leads to focal onset with secondary generalization. - Headache
a. Migraine like headache-Chronic headaches with nausea and vomiting
b. Headaches associated with intracranial hypertension and indicative of hydrocephalus
c. Headaches due to meningitis - Intracranial hypertension (increased pressure within the skull)
a. Most often, intracranial hypertension is due to obstruction of cerebrospinal fluid (CSF) circulation caused by cysticercosis blocking its flow. It may also result from large cysts displacing midline structures, or the so-called cysticercotic encephalitis caused by the inflammatory response to a massive infestation of cerebral parenchyma with cysticerci.
b. These patients may have seizures and deterioration of their mental status with drowsyness and encephalopathy, mainly due to the host’s inflammatory reaction as an exaggerated response to the massive infestation.
c. Stroke like presentation
Stroke may be responsible for the following signs and symptoms: weakness, involuntary movements, gait disturbances, or paresthesias.
d. Neuropsychiatric disturbances
i. Poor performance on neuropsychological tests to severe dementia
ii. Due to many parasites in the brain.
e. Double vision: This is a result of intracranial hypertension, brainstem cysticercosis, or arachnoiditis producing entrapment or compression of cranial nerves III, IV, or VI.
f. Hydrocephalus (Increased water content in the brain)
i. Ten to thirty percent of patients with NCC develop hydrocephalus due to inflammation and fibrosis of the arachnoid villi or inflammatory reaction to the meninges and subsequent occlusion of the foramina of Luschka and Magendie.
ii. Noncommunicating hydrocephalus as a consequence of cysts blocking CSF flow. - Rare presentation of NCC:
a. Spinal NCC: This is rare. It is responsible of symptoms of spinal dysfunction such as radicular pain, weakness, and paresthesias.
b. Ocular cysticercosis:. Patients may present with decreased visual acuity, visual field defects, or blindness.
c. Systemic cysticercosis: The parasites may be located in the subcutaneous tissue or muscle leading to swelling. Peripheral nerve, liver or spleen involvement has been reported.
Diagnosis and workup
CT scan
• CT scan is the preferred imaging study for detection of parenchymal calcifications.
• Depending on the stage of evolution of the infestation, the findings are variable.
MRI
MRI is the imaging modality of choice.MR is also more helpful in evaluation of cystic degeneration and pericystic inflammatory reaction.
MRI, CT findings may sometimes not be conclusive. In such situation the following tests may be done:
• Enzyme-linked immunosorbent assay (ELISA) of CSF
• Enzyme-linked immune-electrotransfer blot assay in serum Stool examination
• Tapeworm carriers may be identified by examining the stool of the patient or relatives of a patient with cysticercosis encephalitis.
Clinical features:
NCC can cause non-specific symptoms such as seizures, headache and focal neurological deficits which can be caused by a number of other pathologies. Hence, there are no specific symptoms or signs that are diagnostic of NCC. Only a rare finding of a live cysticercal cyst seen on fundoscopy in the retina or vitreous of patient with suspected NCC can be considered diagnostic. All patients presenting with new-onset seizures, especially if the seizures are focal with or without secondary generalization should be suspected to have NCC. A search should be performed for any subcutaneous nodules which could indicate subcutaneous cysts, although this finding is rare in those with a single granuloma. Thus, a diagnosis of NCC will require other tests.
Neuroimaging: The mainstay of diagnosis of NCC is neuroimaging using contrast enhanced computerized tomography (CECT) or magnetic resonance imaging (MRI). Both these imaging techniques are expensive, relatively inaccessible to several people in endemic regions and require the use of contrast agents which might have side effects. CT scan is preferred for identifying parenchymal calcifications while MRI is the preferred modality for parenchymal lesions which are in the temporal lobe and frontal lobe close to the skull base, intraventricular cysts and subarachnoid cysts. For patients with SCG, a well performed thin slice CECT scan is as good as an MRI in the detection of the granuloma.
Prevention and treatment
Improved animal husbandry and meat inspection procedures have resulted in the successful interruption of transmission of intestinal T. solium in the United States and Western Europe.62 Tapeworm carriers are good target for the control of cysticercosis/taeniasis. In the developing world, emphasis has been placed on control of the parasite through health education and mass administration of antihelminthic drugs in areas of endemicity in an attempt to remove tapeworm carriers.
Vaccination
Till date no vaccine has been developed against the T. solium .Vaccinating pigs in endemic region to prevent porcine cysticercosis may be good option prevent taeniasis and consequently human cysticercosis. A protective antigen from Taenia ovis oncosphere-stage was cloned to develop a recombinant vaccine for ovine cysticercosis and this vaccine is available commercially for veterinary use in New Zealand.
Treatment
Role of antihelminthic
drugs A meta-analysis and other studies suggest a possible beneficial effect of albendazole in subjects with SCG in the form of improved resolution rates of the granuloma and better seizure control. To make definite conclusions regarding the effect of albendazole in SCG, larger multicentric trials with sound methodology are required. Until such evidence is available, a short course (1–2 weeks) of albendazole (with or without corticosteroids, depending upon the judgment of the treating physician) may be prescribed soon after presentation, i.e., the first seizure.
Role of corticosteroids
While treating individuals with SCG, one can either prescribe a short course of corticosteroids alone (without specific antihelminthic treatment) or antihelminthic drugs (alone or with corticosteroids). The concept of prescribing a short course of corticosteroids alone is in conflict with the practice of administering antihelminthic drugs (alone or with corticosteroids) to individuals with SCG. Large randomized, double-placebo-controlled trial comparing corticosteroids alone, albendazole alone, and albendazole with corticosteroids is required in order to dissect out the benefits accrued due to either agent. Until such evidence is available, definite recommendations regarding the use of corticosteroids alone in the management of SCG cannot be made.
Role of antiepileptic drugs
The risk of seizure recurrence in an individual with SCG is related to the persistence of the enhancing lesion. The currently used AEDs effectively prevent seizure recurrence. It is appropriate to continue AEDs until such time that the lesion (granuloma) is actively degenerating (i.e., appears as an enhancing lesion on imaging studies). The AED may be withdrawn once complete resolution of the granuloma is demonstrated on follow-up imaging studies. The long-term seizure outcome in patients with SCG is generally good. However, the risk of seizure recurrence remains high if the granuloma resolves leaving behind a calcific residue. In the case of resolution with calcification, longer duration of AED should be considered. It is unclear how long AEDs should be administered to individuals with SCG that resolve with calcification. Any AED might be used for much of the period of treatment in individuals with SCG. A newer, non-enzymeinducing AED might be considered for the period of time that antihelminthic treatment is administered.
Compiled & Shared by- Team, LITD (Livestock Institute of Training & Development)
Image-Courtesy-Google
Reference-On Request.
