Ruíz A, Ocampo G, Soto A, José M V
El Colegio de México.
Salud Publica Mex. 1996 Jul-Aug;38(4):249-56.
The degree of aggregation is determined for the whole population and for different age-specific strata and is used for assessing the reinfection rate after a mass antihelminthic chemotherapeutic intervention.
The degree of aggregation of Ascaris lumbricoides is derived from prevalence and intensity of infection date obtained from an epidemiological study of ascariasis carried out in Coatzacoalcos, Veracruz, México by means of maximum likelihood estimation of the negative binomial distribution.
The results show that the distribution of the parasite for the whole population differs from the distribution of the parasite within each age-specific stratum; the reinfection rate is not uniform, the dynamics of the host-parasite association exhibits a clear destabilization of its endemic equilibrium after a first round of mass treatment.
It is suggested that the aggregation among the different age-groups is highly variable and hence the infection and reinfection rates are heterogeneous with regard to age; these states of the host-parasite system are transient. Given the heterogeneity of the infection, the selective treatment seems to be the most adequate strategy to diminish helminth infection rates.
