Vaccination against Taenia solium cysticercosis in underfed rustic pigs of México: roles of age, genetic background and antibody response.

Vaccination of pigs of mixed genetic make-up, raised as rustically as done in rural Mexico, resulted in effective protection to experimental challenge against Taenia solium cysticercosis. Maximum protection was achieved if pigs were immunized at 70 days of age. There was large variation of viable parasite load within vaccinated pigs and controls, which is suggestive of significant genetic factors influencing susceptibility, besides immunization. Our results strengthen the advisability of pig vaccination for control of T. solium cysticercosis, since it lowers the number of viable cysticerci capable of transforming into tapeworms.

Limitations of current diagnostic procedures for the diagnosis of Taenia solium cysticercosis in rural pigs.

The aim of the present study was to evaluate diagnostic procedures for porcine cysticercosis. Sera were obtained from 32 pigs reared in commercial farms, 47 pigs before and after experimental infection, 42 carefully necropsied rural pigs and 191 slaughtered pigs from rural communities in which the presence of the Taenia solium metacestode was assessed by tongue dissection. Sera were analyzed by ELISA to detect antibodies against T. solium antigens and to detect parasite antigens. Most sera from the necropsied rural pigs were also evaluated by the Western blot method. Antigen and antibody ELISA detection assays showed high sensitivity and specificity when applied to sera from pigs reared in commercial farms. In contrast, all methods (Ag-ELISA, Ab-ELISA assays, EITB and tongue inspection) showed lower sensitivity and specificity when applied to the generally lightly infected rurally reared pigs. The probability distribution of cysts in carcasses were also determined. These results emphasize the difficulties in detecting cysticercosis in rural pigs with low levels of cyst burdens.

Prevalence of infection, mean worm burden and degree of worm aggregation as determinants of prevalence of disease due to intestinal helminths.

Theoretical predictions of disease prevalence due to helminth infections based upon a simple probabilistic model which considers the infection prevalence, the mean worm burden and the degree of worm aggregation are presented. A numerical reappraisal of the likely estimates of the degree of aggregation based upon maximum likelihood estimates of the negative binomial distribution is presented. The prevalence of disease shows a positive relationship with the mean worm burden. This association is hyperbolic when helminth parasites are severely aggregated but is s-shaped when helminth parasites tend to be overdispersed. The prevalence of disease decreases with the degree of worm aggregation when the values of the mean intensity are low; as the mean intensity increases this association becomes positive. The relationship between prevalence of disease and prevalence of infection is hyperbolic for severe degrees of parasite aggregation and is s-shaped for intermediate degrees of aggregation. However, if the mean intensity is low and the degree of aggregation is high there could be a negative relationship between the prevalence of disease and the prevalence of infection. The presence of disease due to helminth parasites is feasible for determined ranges of values of the infection prevalence, mean intensity and the degree of worm clumping.

Oscillatory fluctuations in the incidence of rotavirus infections by serotypes 1, 2, 3, and 4.

The statistical evidence for regularity in the epidemic cycles of rotavirus infection for serotypes 1, 2, 3, and 4 was examined. Hospitalization longitudinal data of the monthly incidence of rotavirus infections from the city of Melbourne, Australia during 1977-1993 were used. Periodograms were used for exploring seasonal and longer-term cycles (interepidemic periods) of rotavirus infection. There was a satisfactory agreement between the interepidemic period estimated by means of periodograms with the one predicted by theoretical epidemiological studies. Thus, there is a clear evidence of a biennial peak in the epidemiology of rotavirus. Results of the study show an evidence of the likely existence of an interepidemic cycle of 4.6-5.2 years of duration. The finding of this interepidemic cycle was unexpected, and does not arise from the alternating incidence of the 4 serotypes since this peak appears in the periodogram of each serotype.

Epidemiological model of diarrhoeal diseases and its application in prevention and control.

In this paper, a prototype epidemiological model of acute bacterial and viral diarrhoeal diseases occurring in young children is formulated. The model is able to mimic the observed epidemiological patterns of infantile diarrhoeal diseases associated mainly with enterotoxigenic Escherichia coli or with rotavirus. The proposed mathematical model predicts a plausible pattern of the serological profile of an enteric infection. According to computer simulation experiments (CSE) with this model, it is not necessary to develop an enteric vaccine conferring total and long-lasting immunity in order to achieve protection from diarrhoeal diseases in young children. Given a protective efficacy and a finite duration of vaccine-induced protection, the optimal immunization policy must be sought. Oral rehydration therapy (ORT) intervention has a clear effect in diminishing the number of individuals dying from diarrhoeal illness. The CSE also predict an apparent reduction in age-prevalence of diarrhoeal diseases by use of ORT.

[The omnipresence of helminthiasis]. / La omnipresencia de las helmintiasis.

This article presents a reflexion on the role of helminthic diseases in the world. Emphasis is made on the fact that in spite of its enormous diversity, helminthic parasites have similar epidemiologic behaviours and share high endemicity. Mathematical model design is crucial not only for a better understanding of their transmission mechanisms, but to evaluate different intervention strategies. Nonetheless, control of this serious endemic diseases will be achieved only through the joint effort of governments, funding agencies and researchers.