Implementation of a practical and effective control program for Taenia solium in the Banke District of Nepal

Taenia solium is a zoonotic cestode parasite which causes human neurocysticercosis. Pigs transmit the parasite by acting as the intermediate host. An intervention was implemented in pigs to control transmission of T. solium in Dalit communities of Banke District, Nepal. Every 3 months, pigs were vaccinated with the TSOL18 recombinant vaccine (Cysvax™, IIL, India)) and, at the same time, given an oral treatment with 30mg/kg oxfendazole (Paranthic 10%™, MCI, Morocco). The prevalence of porcine cysticercosis was determined in both an intervention area as well as a similar no intervention control area, among randomly selected, slaughter-age pigs. Post mortem assessments were undertaken both at the start and at the end of the intervention. Participants conducting the post mortem assessments were blinded as to the source of the animals being assessed. At the start of the intervention the prevalence of porcine cysticercosis was 23.6% and 34.5% in the control and intervention areas, respectively. Following the intervention, the prevalence of cysticercosis in pigs from the control area was 16.7% (no significant change), whereas no infection was detected after complete slicing of all muscle tissue and brain in animals from the intervention area (P=0.004). These findings are discussed in relation to the feasibility and sustainability of T. solium control. The 3-monthly vaccination and drug treatment intervention in pigs used here is suggested as an effective and practical method for reducing T. solium transmission, thereby reducing the incidence of human neurocysticercosis. Author summary Neurocysticercosis is a disease caused by a parasitic infection of the brain. The parasite responsible, Taenia solium, is transmitted by pigs where human sanitation is poor and pigs roam freely. Neurocysticercosis is responsible for many cases of epilepsy in people living in poor, developing countries. The feasibility and sustainability of implementing control measures have been major impediments to reducing the incidence of neurocysticercosis. Recently, two new commercial products have become available for pigs which together offer the possibility of interrupting the parasite’s transmission the TSOL18 vaccine (Cysvax™, IIL, India) and an oxfendazole formulation (Paranthic 10%™, MCI, Morocco) licensed for use in pigs for the treatment of cysticercosis. Here we describe the impact of implementing vaccination plus drug treatment of pigs in the Banke district of Nepal. The intervention eliminated the risk of transmission of T. solium by the animals vaccinated and treated during the trial. Application of the vaccination and drug treatment program used here, possibly with strategic use of anthelmintics also in the human population, is an effective option for reducing the incidence of neurocysticercosis in Nepal and elsewhere.


Introduction
In the intervention area, the day of first treatment administration to pigs was defined    Post mortem procedures 155 Animals were purchased having a weight consistent with that at which pigs are commonly 156 sold or slaughtered in the communities. Slaughter weight was determined through advice 157 from the farmers; the mean weight of animals that the farmers indicated were available for 158 slaughter (and which were purchased for post mortem analyses) was 70kg, although 159 individual animal weights ranged from 35kg to more than 175kg. Necropsy procedures 160 undertaken on 110 slaughter-weight pigs at the start of the intervention are described by Sah 161 et al. [8]. Similar procedures were undertaken for the post mortem analyses at the end of the 162 trial but with some variations, as follows. All staff involved in the post mortems were blinded 163 as to whether the animals were from the control or intervention areas. Animals from both 164 areas were necropsied in random order. The animals were transported to a licensed 165 commercial abattoir in Nepalgunj Municipality, Banke where they were euthanized by slaughter house staff according to normal commercial practice processes. The viscera were 167 removed and the heart, liver, lungs, both kidneys and the full diaphragm retained in 168 numbered containers. The organs and the two halves of the carcase, including the head, were 169 refrigerated overnight at 4 °C, after which the carcase was skinned. The tongue, masticatory 170 muscles (both right and left sides) and brain were removed and retained. The muscles from 171 each side of the carcase were dissected from the bones and kept separately. undertaken at the end of the trial, when no cysticerci were detected in the tongue, masticatory 178 muscles, diaphragm, brain or muscles from the right hand side of the carcase, the muscles of 179 the left hand side of the carcase were also sliced. Cysticerci were recorded as viable when      Interventions delivered to individual pigs are summarized in Table 3 during the third intervention period (12 animals) or fourth intervention period (2 animals).

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Three animals which were vaccinated and drug treated at the second intervention were absent 245 at the third intervention period but were present and treated during the fourth intervention.

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The number of animals which were unable to be caught decreased as the trial progressed such 247 that approximately 95% of eligible animals received their vaccinations and oxfendazole 248 treatments during the third and fourth rounds of intervention. During the trial there were 28 pigs which required treatment for wounds (including 13 ear 257 wounds, six scrotal wounds), 11 for respiratory infections and one animal noted with a 258 neurological condition. Treatments administered were long acting oxytetracycline or 259 sulphonamide/ trimethoprim, meloxicam as well as topical treatment of the wounds.  Table 4.    (Table 5). necropsy. This included careful slicing of the entire brain. Nine of these animals had one or 323 more viable T. solium cysticerci in the brain. All those with cysts in the brain also had viable 324 cysts in one or more muscle tissues. None of the 33 pigs from the intervention area had any T. 325 solium cysts in the brain.
Analysis of the characteristics of all animals that were found to be infected with T. infection between the age of the animals and the proportion that was infected (Fig 1).

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Assuming that the infections acquired in young pigs persist, these data suggest that pigs 387 acquire infection relatively early in life and that additional infections do not accumulate as 388 the animals age. An hypothesis that would be consistent with these data would be that pigs

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The intervention that was undertaken in this trial in Nepal was relatively simple. The three-monthly intervention scheme adopted here was predicted to, and did, lead