Vaccination against Taenia solium cysticercosis

Analysis of Immune Responses in Mice Orally Immunized with Recombinant pMG36e-SP-TSOL18/Lactococcus lactis and pMG36e-TSOL18/Lactococcus lactis Vaccines of Taenia solium

Cysticercosis is a cosmopolitan zoonotic parasitic disease infected by larval of Taenia solium (T. solium). Several drugs for the treatment of cysticercosis, such as praziquantel, albendazole, and mebendazole, have certain toxicity and side effects. Considering that there is no vaccine available, we studied a new vaccine for cysticercosis in this study. The complete TSOL18 gene and the optimized SP-TSOL18 gene fragments were obtained using PCR-based accurate synthesis method. The secretory and intracellular recombinant pMG36e-SP-TSOL18/Lactococcus lactis (L. lactis) and pMG36e-TSOL18/L. lactis vaccines of T. solium were prepared. Immune responses in mice orally immunized with these two recombinant L. lactis vaccines were analyzed by the determination of specific antibodies (IgG, IgG1, IgG2a, and sIgA) in serum, spleen lymphocyte proliferation, and cytokines (IL-2, IFN-γ, IL-4, and IL-10) in spleen lymphocyte culture supernatant. Our results showed that, after the first immunization, in these two recombinant L. lactis vaccine groups, the levels of serum specific IgG, IgG2a, and IgG1 increased on 14–56 d and reached the highest level on days 42, 42, and 28, respectively. The level of specific sIgA of intestinal mucosa also increased on 14–56 d and reached the highest level on day 42. The level of spleen lymphocyte proliferation increased on 14–56 d and reached the highest level on day 42. The levels of IL-2, IFN-γ, IL-4, and IL-10 in spleen lymphocyte culture supernatant increased on 14–56 d and reached the highest level on days 42, 42, 28, and 28, respectively. These results indicated that the recombinant pMG36e-SP-TSOL18/L. lactis and pMG36e-TSOL18/L. lactis vaccines can induce specific cellular, humoral, and mucosal immune responses in mice with oral vaccination. More importantly, the recombinant pMG36e-SP-TSOL18/L. lactis vaccine has a better immune effect. In summary, these results demonstrated the possibility of using L. lactis strain as a vector to deliver protective antigens of T. solium.

Therapy for neurocysticercosis

Therapy for neurocysticercosis has advanced during the last 20 years with the advent of albendazole (Zentel) and praziquantel (Cysticide). Albendazole is the current medication of choice for the treatment of neurocysticercosis and is recommended for symptomatic patients with multiple viable cysts in the brain parenchyma. Albendazole may also be useful in extraparenchymal cysticercosis, especially in the subarachnoid racemose form, when complete surgical resection of the cysts is usually impracticable. Currently, there is an intense debate over the value and safety of anticysticercal therapy. Causes for failure of anticysticercal therapy include high inter-individual variability in plasma concentration of albendazole sulfoxide and the complex interactions of several drugs with the albendazole metabolite. Furthermore, albendazole sulfoxide is an enantiomeric mixture of (+)- and (-)-albendazole sulfoxide with accumulation of the (+)-enantiomer in the cerebrospinal fluid. However, the question over which enantiomer is effective against cysticerci remains to be clarified.

State of the art of Taenia solium as compared to Taenia asiatica

Three species of tapeworms infect humans in their adult stage (Taenia solium, Taenia saginata and Taenia asiatica). The 3 are flat, opaque white or yellowish, and exceptional long segmented parasites, measuring 1 to 12 m in their adult stage. In this review, the development of the knowledge regarding the first species, mainly focused on understanding how the larval stage or cysticercus is transmitted to humans, is described. The second species is a cosmopolitan parasite that only causes taeniosis and not cysticercosis; therefore, it will not be included. Information on the third species, which is presently being produced, since this species was recognized as such only at the end of the 20th century, will be discussed at the end of this review.

Evaluating the efficacy of teaching methods regarding prevention of human epilepsy caused by Taenia solium neurocysticercosis in Western Kenya

Taenia solium neurocysticercosis is a major cause of adult-onset epilepsy in developing countries. A questionnaire was administered to 282 Kenyan farmers, followed by a workshop, a second questionnaire, one-on-one training, and a third questionnaire. People who attended workshops were more likely to know how T. solium causes epilepsy in humans in the third visit than the second (P = 0.001). The likelihood that farmers would tether their pigs 100% of the time, limiting exposure to tapeworm eggs, increased after the first (P < 0.001) and second visits (P < 0.001). Farmers were more likely to have heard of Cysticercus cellulosae in the second (P = 0.001) and third visits (P = 0.007), and to know how pigs acquire infection in the second (P = 0.03) and third visits (P = 0.003). Farmers with at least a grade 8 education were more likely to know how T. solium is transmitted to humans in the second (P = 0.001) and third visits (P = 0.009), and were more likely to understand the relationship between epilepsy and T. solium in the second (P = 0.03) and third visits (P = 0.03). Grade 8 education may enhance learning from written material. Workshops followed by individual on-farm training enhanced knowledge acquisition and behavior changes. Training local government extension workers contributed to the sustainability of this project.

Serological responses in porcine cysticercosis: a link with the parasitological outcome of infection

An oral infection model with Taenia solium whole proglottids was used to study host-parasite relationships and the mechanisms underlying resistance to infection in pigs. In addition, an attempt was made to link the parasitological findings to serological data. Groups of six piglets aged 1, 3 and 5 months were infected and slaughtered 3 months p.i. Circulating antibody and antigen levels were monitored weekly. At autopsy total cyst counts were performed. Although the detailed carcass dissection at necropsy revealed a high variation in the number of cysts, the trend was that the number of viable cysts decreased with the age at which the animals were infected. The kinetics of the antigen levels throughout the course of the infection differed markedly between the three age groups of the experimental infection model. In the younger animals, a fast increase in titres of circulating antigen was observed in most animals, reaching a plateau as early as 2 weeks p.i. Besides its faster increase, antigen levels in pigs infected at younger ages also reached higher levels than in older animals and were associated with weaker antibody responses. Results also demonstrated that a relationship exists between the number of cysts and the titre of circulating antigen. This is promising in view of the development of an assay to quantify the progress of an active T. solium infection and would be a useful tool in epidemiological studies to assess the infection burden and the risk of transmission of the disease. The use of specific antibody-detection assays combined with circulating antigen detection could improve our understanding of this relationship.

Genetic polymorphism in Taenia solium cysticerci recovered from experimental infections in pigs

Taenia solium cysticerci recovered from naturally infected pigs from Mexico, Honduras and Tanzania show a clonal structure and local lineages with probable events of genetic recombination without genetic flow within them, as revealed by RAPD. To evaluate genetic polymorphism from cysticerci recovered from experimental infections, 4 pigs were infected with T. solium eggs obtained from tapeworms released by 3 human carriers, a 10-year-old female, a 25-year-old female, and a 44-year-old male, the 4th pig was infected with a mixture of eggs from the 3 tapeworms. Each pig was orally inoculated with 50,000 eggs. After 16 weeks pigs were humanely euthanized and cysticerci were excised. Parasites recovered from each pig were analyzed by RAPD. The proportion of polymorphic loci and the mean heterozygosity as well as a dendogram and an analysis of principal coordinate and minimum spanning tree were obtained. All four pigs developed viable cysticerci; the percent infection was obtained from the ratio of the number of eggs used for infection and the number of cysticerci counted in each pig after necropsy. Infection varied from 0.2 to 4.2%. The values obtained for the proportion of polymorphic loci (0.14-0.55) and the average of expected heterozygosity (0.06-0.22) in the present experimental infection had a broader range than those reported in the literature from natural infections. The dendogram obtained clustered cysticerci into two main groups; the minimum spanning tree allowed to corroborate the data obtained in the dendogram and gave a better discrimination because in a three-dimensional plot it was easier to see that all cysticerci from each tapeworm were clustered amongst themselves. The results obtained could be hypothetically explained because environmental factors and genetic selection agents present in nature influence natural infections but do not participate in experimental ones.

Control of the taeniosis/cysticercosis complex: Future developments

Cysticercosis is due to the establishment of the larval stage of the zoonotic cestode parasite Taenia solium. The infection causes substantial human morbidity and mortality, particularly in several Latin American countries and parts of Africa and Asia, as well as economic losses in pig husban dry due to condemnation of infected pork meat. The life cycle of T. solium includes human beings as definitive hosts and pigs as intermediate hosts. Cysticercosis is acquired by the ingestion of eggs released by human tapeworm carriers, who become infected after ingesting pork meat contaminated with cysticerci. Taenia solium transmission has been associated with poverty, lack of sanitary services and practices of rearing backyard pigs with free access to the areas that villagers use as toilets, as well as cultural behaviour. Nonetheless, due to the recent increase of migration and tourism, industrial countries are also reporting cases of human cysticercosis. There are many epidemiological studies that have been conducted mainly in Latin American countries that have evaluated intervention measures for control of cysticercosis including the development and testing of vaccines. Furthermore, the involvement of international agencies and institutions, such as the World Health Organization, the Food and Agriculture Organization and the International Livestock Research Institute, as well as the commitment of policymakers, scientists and field workers, are key means for the sustainable control and, hopefully, eradication of T. solium infections.

Measures for the prevention and control of Taenia solium taeniosis and cysticercosis

Taeniosis and cysticercosis due to Taenia solium are public health problems in many developing countries. Many studies of this parasitic zoonosis have focused on clinical features, diagnosis, treatment, surveillance, epidemiology and risk factors analysis. More recently projects on community and mass intervention strategies had been conducted in several rural areas worldwide focused on pig vaccination, pig cysticercosis treatment, human mass treatment, infrastructure development, as well as health education campaigns. Their advantages, disadvantages and public health impact have been published. This document discusses the feasibility and limitations of these interventions in order to assist countries in selection the best strategy for the prevention and control of this disease; we emphasized the specific strategies that might be recommended in different demographical situations.

Using electronic technology for Taenia solium education: educating the educators

In Taenia solium endemic areas, intervention programs include a variety of actions aimed to improve sanitary infrastructure and environment, pig husbandry conditions, detection and treatment of tapeworm carries and cysticercosis cases, among others. For a successful long-term effect, these actions must be associated with community participation and health education programs. Prior to designing/conducting health education programs tailored to specific populations, individuals involved in delivering education, as well as other professionals, students, and community leaders, must be well prepared, their knowledge increased, updated or strengthened. Educators must first be well educated to convey clear and accurate messages. Current electronic technology provides invaluable resources for teaching and learning. Learners using electronic materials benefit from a dynamic, non-linear and flexible interaction that can render long lasting effects compared to traditional passive methods. Electronic resources also provide the capability of producing one standardized template, versatile enough to be adapted, translated, modified, and updated. In this presentation, we introduce our preliminary work on the first interactive media presentation on T. solium which will hopefully, soon, become an interactive tutorial that could be utilized in health education in both developing and developed countries.

Control of Taenia solium

Control or eradication of Taenia solium cysticercosis has been achieved to date only in Europe and North America. Significant improvements in sanitary conditions and developing functional slaughterhouse control systems were primarily responsible for control in these regions. Conversely, in endemic areas of developing countries control is limited by economic and sanitary conditions: the life cycle of T. solium is sustained because pigs have access to infected faeces, and cysticercosis-infested pork is available for consumption. Interventional trials with massive human cestocidal chemotherapy, treatment of both human and porcine populations with antihelminthic drugs and/or immunotherapy and health education have shown improvements in specific settings but not yet proven to be sustainable in the long-term. In order to ensure sustainability, any given control strategy towards elimination/eradication of porcine cysticercosis should incorporate economic incentives.

Neurocysticercosis: regional status, epidemiology, impact and control measures in the Americas

The analysis of epidemiological data concerning human cysticercosis point to important advances in understanding the magnitude and distribution of this parasitic disease in Latin America, as well as the relationship of the elements that conform the life cycle of Taenia solium. The data indicate that the main risk factor for acquiring human neurocysticercosis and swine cysticercosis is the presence of the tapeworm carrier in the household. Therefore, several intervention measures for the control of cysticercosis have been evaluated: mass treatment in order to cure tapeworm carriers, health education towards understanding the risk factors, pig control by restraining them, experimental vaccination of pigs and treatment of swine cysticercosis. In this paper, we review the information obtained in these areas. We hope it will be useful in other endemic countries that wish to elaborate an action plan for the control and ultimate eradication of T. solium.

Immune response and protection elicited by DNA immunisation against Taenia cysticercosis

The study evaluated DNA vaccination in Taenia solium cysticercosis prevention by using cDNA of an antigen (cC1) from T. solium metacestode. pcDNA3-cC1 DNA vaccine was constructed by inserting the cDNA into the eukaryotic expression plasmid pcDNA3. Positive expression of the pcDNA3-cC1 product was confirmed by its transfection into COS7 cell and enzyme-linked immunoabsorbent assay using serum of pigs infected with T. solium metacestode. Immunisation of BALB/c mice with three injections of pcDNA3-cC1 induced antigen-specific immune responses of the Th1 phenotype. Inoculation of new-born pigs induced protection against challenge with T. solium by 73.3% reduction of the metacestode number. Antibodies elicited by DNA immunisation with pcDNA3-cC1 specifically reacted with native cC1 protein, which was mainly restricted to the cyst wall of T. solium metacestode. Positive apoptosis signals were also detected in the cyst wall cells of metacestode slices from pigs immunised with pcDNA3-cC1 by TUNEL staining method. Those suggested that apoptosis played a role in protecting pigs immunised with pcDNA3-cC1 nucleic acid vaccine from pathogen challenge.

Castration and pregnancy of rural pigs significantly increase the prevalence of naturally acquired Taenia solium cysticercosis

Cuentepec is a rural village of central Mexico, where 1300 pigs were bred at the time of the study in conditions that favor Taenia solium transmission. The tongues of 1087 (84%) of these pigs were visually examined and 33% were found to be cysticercotic. Castration of male pigs increased prevalence from 23 to 50% (P < 0.001) and pregnancy in sows also increased their prevalence from 28 to 59% (P < 0.001). Thus, endocrinological conditions characterized by low levels of androgens or high levels of female hormones probably influence the susceptibility of pigs to T. solium cysticercosis as observed in mice infected with Taenia crassiceps. Delaying castration of male pigs and confinement of sows during pregnancy might significantly decrease the prevalence of pig-cysticercosis and help curb transmission without much cost or difficulty.

Spinal cord cysticercosis: neurosurgical aspects

Object

The authors report their experience in the treatment of 12 symptomatic patients with intradural spinal neurocysticercosis.

Methods

The mean age of the 12 patients was 33 years. There were eight female and four male patients. Cysticercosis was present in association with hydrocephalus in nine cases. In nine of 12 patients the spinal lesion was confined to the thoracic or lumbar spinal cord, and in three the cysticerci occupied the cervical region. In all patients with hydrocephalus nerve root symptoms developed seven to 48 months later (mean 27.6 ± 15.5 months). In one patient hydrocephalus was absent, but he presented with cysticercal meningitis 24 months before spinal cord compression developed. Presenting symptoms suggesting spinal cysticercosis included muscular weakness (67%), pain (67%), and sphincter disturbance (25%). Neurological examination demonstrated a motor deficit in nine patients, sensory deficit in four, and radicular pain in three. The prognosis was worse in patients with moderate-to-severe arachnoiditis and spinal cord compression compared with those with isolated nerve roots involvement in whom outcome was favorable. Ten patients underwent laminectomy, after which neurological status improved in 44%, remained unchanged in 33%, or worsened in 22.2%.

Conclusions

The authors discuss their findings in these cases. Additionally they briefly review the literature, patho-physiology, and therapeutic and/or surgical strategies involved in this disease.