Cysticercosis - available
Control ToolsDiagnostics availabilityNone in pigs. A number of assays for antibodies to T. solium in humans are now available commercially (E.g Cysticercosis RIDASREEN, Cysticercosis MERLO TEST, MAGIWEL , Immunetics QualiCode cysticercose kit). These use ELISA or western blot technology. GAPS:
None in animals. GAPS:
None for pigs but some have been internationally validated for humans, e.g Immunetics QualiCode cysticercose kit. GAPS:
Methods are described in the OIE Manual of Diagnostic Tests and Vaccines for Terrestrial Animals 2009 Chapter 2.9.5.–Cysticercosis. These include:
WHO FAO OIE guidelines for surveillance and prevention and control of taeniosis/ cysticercosis(2005): chapter 4, pp45-56. Yes. The potential for commercial is there for human cysticercosis, not for porcine cysticercosis. GAP: There is limited production thus affecting distribution and availability in Africa, Latin America and Asia. Not required (antibodies from natural infection can be easily distinguished from antibodies against TSOL18 (recombinant oncosphere protein) or S3Pvac (synthetic peptides). The development of an automated sensitive and specific diagnostic test would greatly reduce the costs of damage to the carcass and also the costs of labour. Ag-ELISAs do have a use in field-based epidemiological studies for indicating transmission. For example, the detection of viable infections in pigs could indicate point sources of infection, season of transmission and age of animals at risk. GAPS:
Vaccines availabilityNone but a T. ovis recombinant vaccine was registered in 1994 by the New Zealand Animal Remedies Board. However, due to market changes in New Zealand, the vaccine is not available commercially. GAP: Full development and availability for routine use. None. None. None. TSOL18 >99% effective in repeated controlled experimental trials and a field trial in Cameroon (Two to 3 vaccinations in combination with treatment were needed to provide high vaccine protection). S3Pvac attained statistically significant reduction in porcine cysticercosis in field trials. GAPS: More field trials with TSOL18. Controlled experimental infection trials with S3Pvac. Duration of immunity. Interference by maternal antibody. None in Europe. The importance of cysticercosis due to T. solium in humans increases the costs of the disease, but it remains to be seen whether the significance of the disease in endemic countries will be sufficient to push commercial production of the vaccine for use in pigs to prevent cysticercosis and to break the chain. Tapeworm vaccines have, in general, not been economically feasible or practical in their implementation. No specific challenges linked to vaccines other than the need to obtain licences or authorisation. No likely regulatory issues for TSOL18. GAPS: The safety and efficacy of the potential vaccine candidate may have to be tested in GLP studies in the pig, where 5-10 times the clinical dose is tested, before regulatory approval. Contact to regulatory authorities is recommended. Feasible to manufacture but will depend on the demand and potential markets. This in turn will be linked to cost especially for the developing countries. Lack of commercial incentives for use of cysticercosis vaccine by poor farmers. Limited but could be used in a region or zone as part of a control programme. GAPS: Costs currently unknown. No large scale production undertaken at present. Combination with commercially valuable porcine vaccine to improve vaccine uptake. TSOL18 vaccine would be no barrier to trade. GAP: Combination with commercially valuable porcine vaccine. Pharmaceutical availabilityPossible use of oxfendazole in pigs but would need to be specially linked to safety and withdrawal periods as the main reason for use would be to kill the cysticerci to ensure no infection of humans eating the meat. Human cysticercosis is currently treated using albendazole, praziquantel or a combination. There is evidence that albendazole is cheaper and more effective than PZQ (Del Brutto et al, 2006. Ann Int Med 145: 43-51). Albendazole has an efficacy of 85 % whereas that of PZQ is even much lower. Treatment of NCC requires a range of treatments from anti-epileptic drugs to placement of a shunt in the case of hydrocephaly. Development of new drugs to treat the cysticerci. GAPS:
Very low. No specific challenge. With praziquantel, albendazole and oxfendazole already on the market it is unlikely that big pharma will endeavor into the costly development of new products. None at present. New developments for diagnostic tests1. The development of an automated sensitive and specific diagnostic test would greatly reduce the costs of damage to the carcass and also the costs of labour. 2. Ag-ELISAs do have a use in field-based epidemiological studies for indicating transmission. For example, the detection of viable infections in pigs could indicate point sources of infection, season of transmission and age of animals at risk. From development through validation to commercial availability will be time consuming (5 to 10 years). The development of an improved diagnostic test is expensive. It is questionable if a potential market is available. GAP: funding. 1. The development of an automated sensitive and specific diagnostic test would greatly reduce the costs of damage to the carcass and also the costs of labour. 2. Ag-ELISAs do have a use in field-based epidemiological studies for indicating transmission. For example, the detection of viable infections in pigs could indicate point sources of infection, season of transmission and age of animals at risk. GAPS:
Comments NA New developments for vaccinesThe TSOL18 which is currently the best available vaccine should be further improved. The ideal vaccine should provide 100% of protection after one dose. Preferably it should be possible to combine the TSOL18 vaccine with other vaccines, e.g. against classical swine fever or in future against African swine fever. Depending on when a candidate vaccine could be identified the timescale will be 5-10 years. Potential vaccines are under trial at present and depending on the outcome will depend the time to commercial availability. Expensive with the need to develop and undertake all the relevant tests to provide data to enable the product to be authorised. The safety and efficacy of the potential vaccine candidate may have to be tested in GLP studies in pigs, where 5-10 times the clinical dose is tested, before regulatory approval. A single shot vaccine might be achieved by pulse-release vaccine formulations or by live recombinant vaccine vectors such as Salmonella which may give a long-lasting immunity after one immunisation. GAP: Protection level when a combined vaccine is administered. New developments for pharmaceuticalsGAPS:
Time to develop would depend on the product and the trials necessary to validate the efficacy and safety. Commercial production would then take further time. Costly. With praziquantel, albendazole and oxfendazole already on the market it is unlikely that big pharma will endeavor into the costly development of new products. Comments NA Disease detailsDescription and characteristics.Humans are the definitive host of the tapeworm (Taenia solium) which causes taeniosis. Cysticercosis occurs when humans and pigs become infected with the larval (metacestodes) stages. GAPS:
The adult stages of T. solium occur in the intestine of humans. The cysticerci of the human tapeworm T. solium cause porcine cysticercosis and occur mainly in muscles and the central nervous system. In heavy infections the liver and other organs of the pig may also be infected. Usually only one adult worm in man, single or multiple larval infections in humans and pigs. GAPS:
The eggs are generally shed inside a proglottid, which remains in the faecal bolus and disintegrates in the environment. The eggs may be disseminated by rain wind and invertebrates and can contaminate vegetation and water. T. solium eggs can survive in the environment for a few weeks or months. GAPS:
Species involvedCysticercosis is an infection of pigs with the larval stages of the parasitic cestode, Taenia solium. GAP: Possible involvement of wild pigs, warthogs, non-human primates. Cysticercosis is an infection caused by the human tapeworm, Taenia solium. Infection occurs when the tapeworm oncospheres enter the body and form cysticerci. The most serious form is neurocysticercosis when cysticerci are found in the central nervous system. Mechanical vectors only. GAP: Role of dung beetles and flies – tracing of faecal contamination. Only humans, pigs, sometimes dogs. GAP: other reservoirs? Description of infection & disease in natural hostsHuman-pig-human, human-human (mechanical, auto-infection). GAPS:
Eggs are shed from infected humans, ingested by pigs, after which the oncospheres penetrate the intestine and migrate to muscle tissue and develop into cysticerci. The parasite life cycle is completed, when humans ingest undercooked pork containing cysticerci. Cysticerci evaginate and attach to the small intestine by their scolex resulting in human tapeworm infection. GAPS:
Usually asymptomatic. The type and severity of the clinical signs depend on the number and location of the larvae. GAPS:
In theory, cysts can be visualised in pigs or felt in tissues such as the tongue of heavily infected animals as early as 2 weeks after infection. Cysticerci are readily visible by 6 weeks and fully developed between 60 to 70 days. None. Adult tapeworms which develop in humans reside in the small intestine for years. Sporadic shedding pattern in humans (short intervals) and production of less than 1000 proglottids. Usually, one to two proglottids are excreted per day, each with approximately 50,000 eggs part of which are immediately infective to pigs and humans when passed. GAP: Proportion of infective eggs of the total number excreted. Development of cysticerci in different tissues in pigs and humans. GAPS:
Zoonotic potentialWorldwide, taeniasis and cysticercosis are common parasitic infections. Cysticercosis and taeniosis are rare in the U.S. and most parts of Europe. GAPS:
High. This is classified as a neglected zoonosis. NCC is not a notifiable disease. NCC requires imaging for diagnosis which leads to an underestimation in areas where such facilities are lacking. GAPS: A major gap. The real prevalence and incidence of taeniosis, cysticercosis and in particular neurocysticercosis need to be assessed. Regional mapping and co-endemicity with other NTD. Linkages with pigs, lack of meat inspection, undercooked meat and poor sanitation/personal hygiene have been identified. Human cysticercosis can occur in local populations even though pork is not eaten and the environment is not shared with pigs if there is a human excreting T. solium eggs in the locality. Auto-infection may occur when tapeworm eggs from a infected individual pass from the intestine back into the stomach, but this has never been proven. GAPS:
Cysticercosis often becomes symptomatic only when cysticerci are developing, disintegrating, dying or become large enough to interfere with blood flow. In the muscles cysticerci do not generally cause symptoms. Sub-cutaneous nodules in humans is common in parts of Latin America and Asia. Although rare in the eyes cysticerci may cause blurry or disturbed vision and may also cause swelling or detachment of the retina. Symptoms of neurocysticercosis depend upon where and how many cysticerci are found in the CNS. Epileptic seizures and headaches are the most common symptoms. Confusion, lack of attention to people and surroundings, difficulty with balance, hydrocephalus may also occur. Death can occur suddenly with heavy infections or in case of low infections when hydrocephalus is created. GAPS:
T. solium eggs spread from human to human, through contaminated food and drinking water or by direct contact. GAPS:
Impact on animal welfare and biodiversityConfinement of the pigs for control. None. GAP: More information needed re wild pigs and non-human primates. None. Geographical distribution and spreadTaenia solium is found principally in Mexico, Central and South America, sub-Saharan Africa, non-Islamic countries of Asia, including India and China where there are free ranging, scavenging pigs and where sanitation is lacking. GAPS:
Endemic; unlikely to occur as an epidemic, but outbreaks have been reported in isolated populations (For example, Orthodox Jews in New York). No, except in pigs where the infection is linked to the period of harvesting – pigs are allowed to roam after harvesting. Depends on the level of infection in humans and the contamination of the environment. GAPS:
Spread by people and infected pig meat sold across borders. No. GAPS:
No. No. GAP: Effects of flooding on dissemination of eggs? No. Route of TransmissionAnimals acquire infection from ingestion of segments and eggs contained in human faeces that contaminate herbage, water, vegetation etc... GAPS:
None clearly defined. GAPS:
Clinically normal humans infected with T. solium excreting high levels of tapeworm eggs in their faeces with little or no sanitation. Poor pig rearing. Poor hand hygiene in humans. GAP: Transmission dynamics models needed. Detection and Immune response to infectionHumoral, cellular and non-specific host responses to cysticerci. A strong protective immunity occurs after natural infection. High levels of protective immunity are induced by antigens in oncospheral extracts. Immunity is largely antibody mediated as evidenced by passive and maternal transfer of immunity. GAPS:
Antibody and antigen detection. GAPS:
Main means of prevention, detection and control
GAPS:
Diagnosis in animals is usually based on the detection of the cysticerci at meat inspection or necropsy. In many endemic countries farmers and pig traders look at the tongue to detect cysts. Light infections are often missed. Tests for antibodies or antigens in serum are not used currently for the diagnosis of cysticercosis in animals except for epidemiological purposes. GAPS:
There is no commercial vaccine available. Two vaccines under development, a recombinant protein vaccine TSOL18 (University of Melbourne) and a synthetic peptide vaccine S3Pvac (Institute Biomedicas, Mexico). Other vaccine candidates described but yet to be confirmed. GAPS:
30mg/kg oxfendazole kills 100% muscle cysts within 4 weeks of dosing; does not kill brain cysts. Dead cysts leave lesions that potentially make the carcase inedible for as long as 6 months. GAPS:
Prevention of contact between pigs or humans with infective tapeworm eggs. GAPS:
Information exists regarding cross-border trade of pigs and introduction of T. solium infection via immigrants. GAPS:
Cysticercosis in pigs can be decreased by preventing or treating T. solium in humans. To prevent infections with T. solium, animals should not be exposed to human faeces. GAP: Effectiveness of alternative control strategies on the incidence rates of infection in humans and pigs in large scale randomised field trials. Generally through meat inspection in abattoirs. Serological tests may be used for epidemiological studies. Large numbers of pigs are home slaughtered and carcases are not controlled. GAPS:
Control of T.solium in humans, combined treatment of tapeworm carriers and of pigs, health education can reduce the levels of infection in pigs and humans. Vaccine trials are underway in pigs in a number of areas worldwide. Combined vaccination with TSOL18 and OXF treatment of pigs was able to eliminate transmission in a hyperendemic area in Cameroon (Assana et al., 2010. Int J Parasitol 40: 515-519). Eradication of T. solium in Europe was possible by a combination of improved pig husbandry (confinement of pigs), meat inspection and better sanitation. GAPS:
Potentially high relative costs for developing countries. Sanitation and restriction of pig movement is the most promising approach in terms of costs and sustainability A pig management educational program was shown to be cost-beneficial for pig infection in Tanzania. GAPS:
Disease information from the OIEYes. http://www.oie.int/en/animal-health-in-the-world/oie-listed-diseases-2011/ No. No reference. General: http://www.oie.int/fileadmin/Home/eng/Health_standards/tahm/2.09.05_CYSTICERCOSIS.pdf Porcine cysticercosis: http://www.oie.int/fileadmin/Home/eng/Health_standards/tahm/2.08.06_PORCINE_CYSTI.pdf Bovine cysticercosis: http://www.oie.int/fileadmin/Home/eng/Health_standards/tahm/2.04.04_BOVINE_CYST.pdf Socio-economic impactInfection is found most often in rural, developing countries with poor hygiene and sanitation where pigs are allowed to roam freely and eat human faeces. This allows the tapeworm lifecycle to be completed and the cycle to continue. Taeniosis and cysticercosis are rare in Muslim countries where eating pork is forbidden. NCC can have very important monetary impact in humans. Review underway to identify costs and case studies under the ICONZ project to assess burdens in selected sites in sub-Saharan Africa + WHO/FERG initiative (global burden). Data available for Cameroon and South Africa. GAPS:
Drugs for epilepsy are cheap, but the treatment has usually to be continued for the whole life. Control should be focused on sanitation, hygiene and better pig management. Building and maintenance of latrines, building pig pens and especially buying feed for pigs is quite expensive although there are also better returns. Treatment of taeniosis cases would be very expensive due to the cost of diagnosis and the low prevalence of infection in humans. Diagnosis and treatment of neurocysticercosis are expensive (CT or MRI scans needed). GAPS:
Probably none. GAP: Impact of infection on pig fertility and growth? None. Cysticercosis causes economic loss through condemnation of infected meat and offal. In Africa, there are reports of losses related to a lower commercial value (reduction of 30 to 50%) of infected live pigs detected on the basis of the tongue test. GAP: Economic loss in pigs in Latin America and Asia? Trade implicationsNone as there are currently no rules re trade apart from the need to ensure meat is subject to meat inspection and certified fit for human consumption. The OIE Terrestrial Animal Health Code 2009 does not currently include a chapter on cysticercosis. None as there are no rules re trade apart from the need to ensure meat is subject to meat inspection and certified fit for human consumption and can be placed on the market. None as there are no rules re trade apart from the need to ensure meat is subject to meat inspection and certified fit for human consumption. Main perceived obstacles for effective prevention and control
GAP: Need for randomized controlled field trials to test the effectiveness of such control measures. Main perceived facilitators for effective prevention and controlThe following facilitators can play a role:
RiskMain risk from animals is infection of humans and the difficulty in breaking the cycle. Development and increase of NCC cases in Europe through immigration of tapeworm carriers from endemic countries. ConclusionCysticercosis is of major importance in the developing world where it is a neglected zoonoses and where the neural form is grossly under diagnosed. The natural history of NCC remains unknown. Very little is known about the symptoms and burden of NCC. The frequency of cysticercosis and NCC worldwide is unknown. Control of the tapeworm in humans is important, but treatment is challenging due to the difficulty in finding the very few cases that exist. Hence, the most sustainable and cost-effective method may be (this has not been tested, but is suggested by transmission dynamics models) good sanitation and to prevent contact between pigs and tapeworm eggs excreted by people. Condemnation or thorough cooking of infected meat is important but in poor areas the presence of meat inspection is unlikely and the discarding of infected meat is impossible to achieve. Control of infection in pigs either by vaccination or pre slaughter treatment with a compound which kills the cysticerci is possible although their costs and application may be too high to enable implementation in developing countries. |
