Successful Antiparasitic Treatment for Cysticercosis is Associated with a Fast and Marked Reduction of Circulating Antigen Levels in a Naturally Infected Pig Model

Porcine model of neurocysticercosis by intracarotid injection of Taenia solium oncospheres: Dose assessment, infection outcomes and serological responses

BACKGROUND

Neurocysticercosis (NCC) is the infection of the human central nervous system (CNS) by Taenia solium larvae that cause significant neurological morbidity. Studies on NCC pathophysiology, host-parasite interactions or therapeutic agents are limited by the lack of suitable animal models. We have previously reported that carotid injection of activated T. solium oncospheres directs parasites into the CNS and consistently reproduces NCC. This study assessed the minimal dose required to consistently obtain NCC by intracarotid oncosphere injection and compared antigen and antibody response profiles by dose-group.

METHODS/PRINCIPAL FINDINGS

Three groups of pigs were infected with either 2500 (n = 10), 5000 (n = 11), or 10000 (n = 10) oncospheres. Two pigs died during the study. Necropsy exam at day 150 post-infection (PI) demonstrated viable NCC in 21/29 pigs (72.4%), with higher NCC rates with increasing oncosphere doses (4/9 [44.4%], 9/11 [81.8%] and 8/9 [88.9%] for 2500, 5000, and 10000 oncospheres respectively, P for trend = 0.035). CNS cyst burden was also higher in pigs with increasing doses (P for trend = 0.008). Viable and degenerated muscle cysticerci were also found in all pigs, with degenerated cysticerci more frequent in the 2500 oncosphere dose-group. All pigs were positive for circulating parasite antigens on ELISA (Ag-ELISA) from day 14 PI; circulating antigens markedly increased at day 30 PI and remained high with plateau levels in pigs infected with either 5000 or 10000 oncospheres, but not in pigs infected with 2500 oncospheres. Specific antibodies appeared at day 30 PI and were not different between dose-groups.

CONCLUSION/SIGNIFICANCE

Intracarotid injection of 5000 or more oncospheres produces high NCC rates in pigs with CNS cyst burdens like those usually found in human NCC, making this model appropriate for studies on the pathogenesis of NCC and the effects of antiparasitic treatment.

Performance of Ag-ELISA in the diagnosis of Taenia solium cysticercosis in naturally infected pigs in Tanzania

Background

Taenia solium is a zoonotic parasite responsible for neurocysticercosis—a major cause of late-onset acquired epilepsy in humans. Lack of affordable, specific and sensitive diagnostic tools hampers control of the parasite. This study assessed the performance of an antigen detection enzyme-linked immunosorbent assay (Ag-ELISA) in the diagnosis of viable T. solium cysticercosis in naturally infected slaughter-age pigs in an endemic area in Tanzania.

Methods

A total of 350 pigs were bled before they were slaughtered and their carcases examined. Serum was analyzed for circulating antigens by using a monoclonal antibody-based B158/B60 Ag-ELISA. Each carcase was examined for the presence of Taenia hydatigena cysticerci and half carcase musculature together with the whole brain, head muscles, tongue, heart and diaphragm were sliced with fine cuts (< 0.5 cm) to reveal and enumerate T. solium cysticerci. Half carcase dissection can detect at least 84% of infected pigs. Prevalence and their 95% confidence intervals (CI) were calculated in Stata 12. Sensitivity, specificity, predictive values and likelihood ratios were determined.

Results

Twenty–nine pigs (8.3%, 95% CI: 5.6–11.7%) had viable T. solium cysticerci while 11 pigs had T. hydatigena cysticerci (3.1%, 95% CI: 1.6–5.5%). No co-infection was observed. Sixty-eight pigs (19.4%, 95% CI: 15.4–20%) tested positive on Ag-ELISA; of these, 24 had T. solium cysticerci and 7 had T. hydatigena cysticerci. Sensitivity and specificity were determined to be 82.7% and 86.3%, respectively. Positive and negative predictive values were 35.2% and 98.2%, respectively. Likelihood ratios for positive and negative Ag-ELISA test results were 6.0 and 0.2, respectively. There was a significant positive correlation between the titre of circulating antigens and intensity of T. solium cysticerci (r₍₃₄₈₎ = 0.63, P < 0.001).

Conclusions

The Ag-ELISA test characteristics reported in this study indicate that the test is more reliable in ruling out T. solium cysticercosis in pigs, than in confirming it. Hence, a negative result will almost certainly indicate that a pig has no infection, but a positive result should always be interpreted with caution. Estimates of T. solium prevalence based on Ag-ELISA results should, therefore, be adjusted for test performance characteristics and occurrence of T. hydatigena.

Natural History of Treated Subarachnoid Neurocysticercosis

Subarachnoid neurocysticercosis (SUBNCC) is usually caused by an aberrant proliferative form of Taenia solium causing mass effect and arachnoiditis. Thirty of 34 SUBNCC patients were treated with extended cysticidal and anti-inflammatory regimens and followed up a median of 4.2 years posttreatment (range: 15 for ≥ 4 years, 20 ≥ 2 years, 26 > 1 year, and 3 < 1 year). The median ages at the time of first symptom, diagnosis, and enrollment were 29.7, 35.6, and 37.9 years, respectively; 58.8% were male and 82.4% were Hispanic. The median time from immigration to symptoms (minimum incubation) was 10 years and the estimated true incubation period considerably greater. Fifty percent also had other forms of NCC. Common complications were hydrocephalus (56%), shunt placement (41%), infarcts (18%), and symptomatic spinal disease (15%). Thirty patients (88.2%) required prolonged treatment with albendazole (88.2%, median 0.55 year) and/or praziquantel (61.8%; median 0.96 year), corticosteroids (88.2%, median 1.09 years), methotrexate (50%, median 1.37 years), and etanercept (34.2%, median 0.81 year), which led to sustained inactive disease in 29/30 (96.7%) patients. Three were treated successfully for recurrences and one has continuing infection. Normalization of cerebral spinal fluid parameters and cestode antigen levels guided treatment decisions. All 15 patients with undetectable cestode antigen values have sustained inactive disease. There were no deaths and moderate morbidity posttreatment. Corticosteroid-related side effects were common, avascular necrosis of joints being the most serious (8/33, 24.2%). Prolonged cysticidal treatment and effective control of inflammation led to good clinical outcomes and sustained inactive disease which is likely curative.

Performance of a Sandwich Antigen-Detection ELISA for the Diagnosis of Porcine Taenia solium Cysticercosis

The pig is the natural intermediate host of Taenia solium, a parasite causing significant burden of disease in both humans and pigs. Porcine cysticercosis is traditionally detected via tongue palpation and slaughterhouse meat inspection, both with limited sensitivity. Serum antibody detection has a better performance; however, it does not discriminate past from present infection. Serum antigen detection can demonstrate viable infection and gives a good estimate of parasitic load. This study evaluated a sandwich antigen-detection ELISA using monoclonal antibodies (MoAbs) 158C11 and 60H8 for the diagnosis of viable cysticercosis in pigs. Serum samples were used from 35 naturally T. solium cysticerci-infected pigs, 31 cysticercosis-negative pigs, and 22 pigs with Taenia hydatigena infection (to assess cross-reactions). Positive cysticercosis samples were subcategorized at necropsy according to parasitic burden as mild (1-10 viable cysts, n = 10), moderate (11-100 cysts, n = 5), or severe infection (more than 100 cysts, n = 20). This Ag-ELISA showed a sensitivity of 82.9% and a specificity of 96.8% when not considering cross-reactions with T. hydatigena. Hundred percentage of severely infected, 80% of moderately infected, and 50% of mildly T. solium-infected pigs tested positive. Twenty of 22 pigs with only T. hydatigena infections were positive, with 13 reaching saturating levels in the ELISA. The Ag-ELISA revealed the presence of live cysts and is, thus, a fairly reliable test to monitor experimental infection, response to treatment, and follow-up in animal models of cysticercosis. It should, however, be carefully interpreted when used in regions where T. hydatigena is endemic in pigs.

Oxfendazole: a promising agent for the treatment and control of helminth infections in humans

INTRODUCTION

Oxfendazole (methyl [5-(phenylsulphinyl)-1H benzimidazole-2-yl] carbamate) has a particularly long metabolic half-life in ruminants, and its metabolite fenbendazole also has anthelminthic action. A very limited number of drugs are available for the treatment of some zoonotic helminth infections, such as neurocysticercosis and echinococcosis. More recent work has expanded oxfendazole's nonclinical safety profile and demonstrated its safety and bioavailability in healthy human volunteers, thus advancing the possibility of a new and greatly needed option for antiparasitic treatment of geohelminths and tissue parasites. Areas covered: The present article reviews evidence supporting the safety and efficacy of oxfendazole against both gut and tissue dwelling helminths in animals, as well as more recent safety and pharmacokinetic data supporting its potential for use in human parasitoses. Expert commentary: The pharmacokinetics, safety, and wide spectrum of efficacy of oxfendazole are consistently demonstrated in intestinal helminth infections of animals as well as in tissue dwelling larval cestode and trematode infections in diverse animal species. Now supported by first-in-human safety and pharmacokinetic data, oxfendazole becomes a promising alternative to the limited portfolio of antiparasitic drugs available to treat helminthic diseases of humans.

Neurocysticercosis in Pregnancy

The normal physiologic changes during pregnancy contribute to nutritional, metabolic, and immunologic adjustments, which can have an impact on the presentation of several diseases. New onset seizures during pregnancy and the postpartum can be attributed to several etiologies. Patient demographic data as well as personal and social histories are key in determining the etiology of new onset seizures. Neurocysticercosis (NCC), a commonly overlooked etiology, must be included in the differential diagnosis of patients with new onset seizures coming from NCC endemic areas. The diagnosis is based on a combination of clinical findings, exposure history, imaging, and serology. We present two cases of patients with NCC that became symptomatic during pregnancy or postpartum period. We will review the epidemiology, clinical manifestations, and management of NCC in pregnancy.

Target product profiles for the diagnosis of Taenia solium taeniasis, neurocysticercosis and porcine cysticercosis

Target Product Profiles (TPPs) are process tools providing product requirements to guide researchers, developers and manufacturers in their efforts to develop effective and useful products such as biologicals, drugs or diagnostics. During a WHO Stakeholders Meeting on Taenia solium diagnostics, several TPPs were initiated to address diagnostic needs for different stages in the parasite's transmission (taeniasis, human and porcine cysticercosis). Following the meeting, draft TPPs were completed and distributed for consultation to 100 people/organizations, including experts in parasitology, human and pig cysticercosis, diagnostic researchers and manufacturers, international organizations working with neglected or zoonotic diseases, Ministries of Health and Ministries of Livestock in some of the endemic countries, WHO regional offices and other interested parties. There were 53 respondents. All comments and feedback received were considered and discussions were held with different experts according to their area of expertise. The comments were consolidated and final TPPs are presented here. They are considered to be live documents which are likely to undergo review and updating in the future when new knowledge and technologies become available.

Update on the Diagnosis and Management of Neurocysticercosis

Neurocysticercosis is an important cause of seizures worldwide and is endemic in most of Latin America, Sub-Saharan Africa, Southeast Asia, India, and China. Neurocysticercosis has profoundly different disease manifestations varying from asymptomatic presentation to life-threatening hydrocephalus. Clinical manifestations, pathogenesis, diagnostic methods, and optimal treatment vary with the location, number of lesions, and host response. Diagnosis is based on a combination of clinical presentation, neuroimaging findings, history of exposure, and serologic testing. Initial therapy should be focused on symptom management including seizure control and management of increased intracranial pressure. Emerging data are demonstrating that the optimal management approach varies with stage. Single enhancing or cystic lesions should be treated with albendazole and steroids. Patients with more than two cystic lesions should be treated with combination therapy with albendazole and praziquantel, whereas patients with hydrocephalus benefit from surgical management, especially with minimally invasive approaches.