THE DEGREE OF AGE-AGGREGATION OF ASCARIS- LUMBRICOIDES IN A COMMUNITYAFTER A MASS ANTIHELMINTHIC INTERVENTION

Objective. The degree of aggregation is determined for the whole popul ation and for different age-specific strata and is used for assessing the reinfection rate after a mass antihelminthic chemotherapeutic inte rvention. Material and methods, The degree of aggregation of Ascaris l umbricoides is derived from prevalence and intensity of infection data obtained from an epidemiological study of ascariasis carried out in C oatzacoalcos, Veracruz, Mexico by means of maximum likelihood estimati on of the negative binomial distribution. Results. The results show th at the distribution of the parasite for the whole population differs f rom the distribution of the parasite within each age-specific stratum; the reinfection rate is not uniform; the dynamics of the host-parasit e association exhibits a clear destabilization of its endemic equilibr ium after a first round of mass treatment. Conclusions. It is suggeste d that the aggregation among the different age-groups is highly variab le and hence the infection and reinfection rates are heterogeneous wit h regard to age; these states of the host-parasite system are transien t. Given the heterogeneity of the infection, the selective treatment s eems to be the most adequate strategy to diminish helminth infection r ates.