How to eliminate taeniasis/cysticercosis: porcine vaccination and human chemotherapy (Part 2)

Abstract

Background: The application of effective vaccines against pig cysticercosis and mass chemotherapy against pig cysticercosis and human taeniasis have shown the feasibility of interrupting the parasite's life cycle in endemic areas.

Methods: A mathematical model that divides the population into susceptible, infected, and vaccinated individuals is formulated. The model is based upon the life cycle of the parasite. Computer numerical simulation experiments to evaluate the impact of pig vaccination under different vaccination schedules, and combined intervention strategies including pig vaccination and anthelmintic treatment against human taeniasis are carried out.

Results: Vaccination against either pig cysticercosis or against human taeniasis will influence the transmission dynamics not only among vaccinees but also the dynamics of the other hosts as well. When the protective efficacy and/or the coverage rate is less than 100%, different mass interventions like vaccinating the pig population twice in combination with chemotherapeutic treatment against human taeniasis, the elimination of the infection in both pigs and humans can also be achieved.

Conclusions: Our mathematical model has the potential for planning, and designing effective intervention strategies including both mass vaccination and/or chemotherapeutic treatment to eliminate pig cysticercosis, human taeniasis and human neurocysticercosis. The model can be adapted to any given community with mild, moderate endemicity, or even in hyperendemic regions.

Keywords: Chemotherapeutic interventions; Computer simulation experiments; Elimination; Eradication; Public health; Susceptible-infected mathematical model; Taenia-cysticercosis; Vaccination strategies.

Fig. 1

Two doses of vaccination with efficacy and coverage 100% (Table 1). In all graphs: human taeniasis (blue), human cisticercosis (yellow), human cisticercosis (red). In a, b, c, and d the vaccine is first applied to pigs of two weeks of age, and the second round is applied when pigs reach the age of 11 months with 25 days. In e, the 2 doses are applied but the second dose is administered to pigs of 11 months of age. In f, there is no vaccination. a) Mean worm intensities; b) Susceptibles; c) Prevalence of infected hosts; d) Phase spaces; e) Prevalence of infected hosts; f) Mean worm intensities in control. Ro = 5.49;  p_C = 0.82

Fig. 2

Prevalence of infection in pig (line red), human cysticercosis (line yellow), and human taeniasis (line blue) with vaccine efficacy equal to 100% and coverage at 82%. Only one dose of vaccination to pigs of two weeks old. Ro = 5.49;  p_C = 0.82

Fig. 3

Vaccine efficacy is 100% and coverage rate is 82%. In all graphs: human taeniasis (blue), human cisticercosis (yellow), human cisticercosis (red). In a and b, the vaccine is applied to pigs of one week of age and the second dose is given later to pigs of 12 months and 9 days of age. Simultaneously, chemotherapy is applied to both pigs and humans. In c, the same immunization protocol is followed as in a and b, but no chemotherapy is applied. a) Mean worm intensities; b) Prevalence of infected hosts; c) Prevalence of infected hosts. The coverage rate and the efficacy of the anthelmintic drugs in pigs and humans is 90 and 90%, respectively. Ro = 5.49;  p_C = 0.82

Fig. 4

Vaccine efficacy 82% and coverage 82%. The vaccination strategy includes three doses: the first dose is given to newborn pigs, the second is applied to pigs of one month of age, and the third dose is for pigs with 12 months plus 24 days of age. In all graphs: human taeniasis (blue), human cisticercosis (yellow), human cisticercosis (red). a) Mean worm intensities; b) Prevalence of infected hosts. Ro = 5.49;  p_C = 0.82

Fig. 5

Vaccine efficacy is 100% and coverage rate is 82%. Prevalence of infection in pigs (black-dotted line). Vaccination is applied to: a) pigs at 6 months of age (red arrow) b) pigs at 6 and 12 months of age (red arrows). Ro = 5.49;  p_C = 0.82

Fig. 6

Vaccine efficacy 82% and coverage 60%. In all graphs: human taeniasis (blue), human cisticercosis (yellow), human cisticercosis (red). The vaccination strategy includes three doses: the first dose is given to newborn pigs, the second is applied to pigs of one month of age, and the third dose is for pigs with 14 months plus 24 days of age. Concomitantly to the vaccination strategy for pigs, chemotherapy against human taeniasis is administered to humans of 14 and 16 months of age. a) Mean worm intensities; b) Prevalence of infected hosts. Ro = 5.49;  p_C = 0.60