Question

Macroparasites are rarely distributed throughout a host population in a
uniform manner. Describe the types of parasite distributions that occur
in the field. Explain what processes generate these distributions and
why they are important in evaluating the control and treatment of
parasitic infections in host populations.

Answer 1

Macro-parasites infections are chronic & tend to cause density-dependent pathology (the more no. of macro-parasites, more likely host is to suffer reduced fitness). To find the types of distribution we have to find the variance to mean ratio. When variance/mean ratio is 1, it followed Poisson distribution; when variance/mean ratio is greater than 1 (negative binomial distribution), distribution is over dispersed, i.e., an aggregated distribution; when variance/mean ratio is less than 1 (regular binomial distribution), we have under dispersion. It is found that macro-parasites distribution follows the aggregated distribution. If parasite infection rates are constant among hosts, parasites will have a Poisson distribution & they will not aggregately distributed. But infection rates vary among hosts. This is due to the heterogeneity in parasite distributions in the environment, variation in host susceptibility etc. Thus in reality infection rates vary & macro-parasites follow aggregated distribution. Through this distribution we can know the individual susceptibility & transmission potential of particular species in macro-parasite transmission. It can helpful for controlling & treatment of parasitic infections in host populations. It also impacts the stability of host population dynamics.