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- A Proposal for Classification of Neurocysticercosis cjns.org | Cysticercosis (Neurocysticercosis) medic8.com | Reversible hemifacial spasm due to neurocysticercosis Sushil Razdan, KK... annalsofian.org |
Cysticercosis, or neurocysticercosis, is the most common parasitic infestation of the central nervous system worldwide.[1] Humans develop cysticercosis when they ingest eggs or larvae of the tapeworm Taenia solium. The eggs and larvae are usually found in fecally-contaminated water or food and in undercooked pork. Autoinfection as a result of the entry of eggs into stomach due to retroperistalsis or as a result of accidental ingestion of eggs from the host's own feces due to contaminated hands is also possible.[2]
[edit] AgentThe cause of human cysticercosis is the larval form of Taenia solium (pork tapeworm). T. solium is a platyhelminth of the cestoidean class, the cyclophyllidea order and the taeniidae family. The common larval stage of T. solium was also known as Cysticercus cellulosae. [edit] History of DiscoveryThe earliest reference to tapeworms were found in the works of ancient Egyptians that date back to almost 2000 BC. [3] The description of measled pork in the History of Animals written by Aristotle (384–322 BC) showed that the infection of pork with tapeworm was known to ancient Greeks at that time.[3] It was also known to early Muslim physicians and was one of the reasons for pork being forbidden by Islamic dietary laws.[4] Recent examination of evolutionary histories of hosts and parasites and DNA evidence show that over 10,000 years ago, ancestors of modern humans in Africa became exposed to tapeworm when they scavenged for food or preyed on antelopes and bovids, and later passed the infection on to domestic animals such as pigs. [5] Cysticercosis was described by Johannes Udalric Rumler in 1555; however, the connection between tapeworms and cysticercosis had not been recognized at that time. [6] Around 1850, Kuchenmeister fed pig meat containing cysticerci of T. solium to humans awaiting execution in a prison, and after they had been executed, he recovered the developing and adult tapeworms in their intestines. [3][6] By the middle of the 19th century, it was established that cysticercosis was caused by the ingestion of the eggs of T. solium. [7] [edit] TransmissionPigs and humans are T. solium reservoirs. Humans can be infected by ingesting the eggs or larvae from eating undercooked pork that contains viable cysticercosis larvae or from fecally contaminated food or water. [8] The adult tapeworm develops in humans after the ingestion of infected meat; however cysticercosis occurs after the ingestion of eggs, either from external sources or from their own feces.[8] Pigs get infected with cysticerci when they ingest human feces. The incubation period ranges from months to over ten years. [9] [edit] MorphologyT. solium worms may reach a length of several meters [8]. The scolex has four suckers, and a double crown of prominent hooks, which attach to the intestinal mucosa. [8] T. solium eggs are spherical and 30 to 40 μm in diameter. [9] The cysticercus larva completes development in about 2 months. It is semitransparent, opalescent white, and elongate oval in shape and may reach a length of 0.6 to 1.8 cm. [8] [edit] Life cycleThe life cycle involves humans as a definite host and pigs as an intermediate host. Pigs ingest contaminated food or water that contains eggs or proglottids from human’s feces. The ova develop into cysticercus in pig muscles. Human becomes infected when they ingest raw or undercooked “measly pork” that contains viable cysticercus. Upon reaching the small intestine, the scolex attaches to the intestinal wall and a proglottid chain grows. T. solium releases three to six proglottids/day, bearing 30,000 to 70,000 eggs (ova) per proglottid into the intestine. Nearly 250,000 ova are passed daily into the human feces and to the environment, and the cycle continues.[9] Infections with cysticercus occur after humans consume the ova from exogenous sources or through self-infection via the fecal-oral route. Humans, in this case, are intermediate hosts. Ova are digested in the stomach and release oncospheres which penetrate the intestinal wall and reach the bloodstream. [10] These oncospheres develop into cysticerci in any organ but are common in brain, subcutaneous tissue, or eyes. [edit] Clinical Presentations in humansCysticercosis in muscles Neurocysticercosis Stage 3 is typified by colloid or degenerating cysts with thick cystic fluid, thickened capsule, and appear two to 10+ years after the cyst becomes mature. The cyst no longer prevents a host immune response and its antigens leak from the bladder wall. The intense inflammation is provoked around the degenerating cyst. Most patients bearing stage 3 develop clinical signs and symptoms such as seizures, occasional focal neurological signs, headaches, nausea, vomiting, lethargy from increased intracranial pressure and altered mental status. [9] At stage 4, the cyst is calcified. The surrounding inflammation drops since the dead cyst no longer produces foreign antigens. Common clinical features includes persistent non-provoked seizures although most of the patients are asymptomatic. [9] In meningeal cysticercosis, cysticerci often do not develop into typical cysts, and become racemose, lacking a scolex and becoming lobes in thin-walled bladders. These cysts increase and slowly leak their antigen into the subarachnoid CSF producing meningitis and can further develop into arachnoiditis, which may lead to obstructive hydrocephalus, cranial nerve involvement, intracranial hypertension, arterial thrombosis and stroke. [8][9] In intraventricular cysticercosis, the cysts occur in the lateral, third or fourth ventricles which may be asymptomatic or if they block the flow of CSF, they may cause increased intracranial pressure. [9] Ophthalmic Cysticercosis Subcutaneous Cysticercosis [edit] DiagnosisThe traditional method of demonstrating T. solium eggs in stool samples diagnoses only taeniasis.[10] Though the presence of T. solium eggs or proglottids in the feces does not necessary mean the infection with cysticercus, those patients should be evaluated serologically, since autoinfection via fecal-oral route can potentially result in cysticercosis. In CDC’s immunoblot assay, cysticercosis-specific antibodies can react with structural glycoprotein antigens from the larval cysts of T. solium.[10] Therefore, the serum samples from patients with other microbial infections do not react with any of the T. solium derived antigens. The positions of the seven diagnostic glycoproteins are marked and selected based on how fast they can move in SDS-PAGE. The test is so far 100% specific and has higher sensitivity than any other immunoassay systems. Neuroimaging with CT or MRI is the most useful method to diagnose neurocysticercosis. [9] CT scan shows both calcified and uncalcified cysts, as well as distinguishing active and inactive cysts (2). MRI can detect intraventricular cysts while CT scan cannot. [9] [edit] Management and TherapyTreatment must be tailored to the specific needs of the patient and may include medical drugs such as antihelminthic drugs and corticosteroids or surgery.[12] Surgical treatment includes direct excision of ventricular cysts, shunting procedures, and removal of cysts via endoscopy.[8][9] Albendazole is preferable over praziquantel due to its lower cost and corticosteroids and anticonvulsants do not reduce CSF and brain drug levels. [9] Moreover, the results from meta-analysis study have shown that albendazole is more effective than praziquantel in terms of clinically important outcomes in patients with neurocysticercosis [13] [edit] Public Health and Prevention StrategiesCysticercosis is considered as “tools-ready disease” according to WHO [14]. International Task Force for Disease Eradication in 1992 reported that cysticercosis is potentially eradicable. [15] It is feasible because there are no animal reservoirs besides humans and pigs. The only source of T. solium infection for pigs is from humans, a definite host. Theoretically, breaking the life cycle seems easy by doing intervention strategies from various stages in the life cycle..[16] For example, (a) Massive chemotherapy treatment of infected humans, improving sanitation, and education humans are major ways to discontinue the cycle at step 1, in which eggs from human feces are transmitted to other humans and/or pigs. (b) Cooking of pork or freezing it and inspecting meat are effective means to cease the life cycle at step 3. (c) The management of pigs by treating them or vaccinating them is another possibility to intervene step 4 of the life cycle. Intervention by concurrent treatment of humans and pigs The intervention strategies to eradicate cysticercosis includes surveillance of pigs in foci of transmission and massive chemotherapy treatment of humans. [15] In reality, control of T. solium by a single intervention, for instance, by treating only human population will not work because the existing infected pigs can still carry on the cycle. The proposed strategy for eradication is to do multilateral intervention by treating both human and porcine populations.[17] It is feasible because treatment pigs with oxfendazole have been shown to be effective and once treated, they are protected from further infections for at least 3 months.[18] Limitations Even with the concurrent treatment of humans and pigs, complete elimination is hard to achieve. In one study conducted in 12 villages in Peru, both humans and porcine were treated with praziquantel and oxfendazole, with the coverage of more than 75% in humans and 90% in pigs [19] The result shows a decreased in prevalence and incidence in the intervention area; however the effect did not completely eliminate T. solium. The possible reason includes the incomplete coverage and re-infection. [20] Even though T. solium could be eliminated through mass treatment of human and porcine population, it is not sustainable.[17] Moreover, both tapeworm carriers of humans and pigs tend to spread the disease from endemic to non-endemic areas resulting in periodic outbreaks of cysticercosis or outbreaks in new areas. [21][22] Given the fact that pigs are part of a life cycle, vaccination of pigs is another feasible intervention to eliminate cysticercosis. Research studies have been focusing on vaccine against cestode parasites, since many immune cell types are found to be capable of destroying cysticercus.[23] Many vaccine candidates are extracted from antigens of different cestodes such as T. solium, T. crassiceps, T. saginata, T. ovis and target oncospheres and/or cysticerci. In 1983, Molinari et al. reported the first vaccine candidate against porcine cysticercosis using antigen from cysticercus cellulosae drawn out from naturally infected. [24] Recently, vaccines extracted from genetically engineered 45W-4B antigens have been successfully tested to pigs in an experimental condition. [25] This type of vaccine can protect against cysticercosis in both Chinese and Mexican type of T. solium. However, it has not been tested in endemic field conditions, which is important because the realistic condition in the field differ greatly from experimental condition, and this can result in a great difference in the chances of infection and immune reaction. [23] Other types of interventions and Limitations [edit] EpidemiologyThe tapeworm that causes cysticercosis is endemic to many parts of the world including China, Southeast Asia, India, sub-Saharan Africa, and Latin America. Some studies suggest that the prevalence of cysticercosis in Mexico is between 3.1 and 3.9 percent. Other studies have found the seroprevalence in areas of Guatemala, Bolivia, and Peru as high as 20 percent in humans, and 37 percent in pigs.[33] In Ethiopia, Kenya and the Democratic Republic of Congo around 10% of the population is infected, in Madagascar 16%. The frequency has decreased in developed countries owing to stricter meat inspection, better hygiene and better sanitary facilities. The distribution of cysticercosis coincides with the distribution of T. solium. [34] In Latin America, an estimated 75 million persons live in endemic areas and 400,000 people have symptomatic disease.[35] Cysticercosis is also found to be associated with Hispanic ethnicity, immigrant status, and exposure to areas of endemicity.[8] In the US, the disease is found in immigrants from Mexico, Central and South America. Current livestock for pigs in the U.S do not play a role in the transmission of Taenia solium, and thus cysticercosis in the U.S is an imported disease.[16] [edit] In popular culture
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