ONCHOSIM: a model and computer simulation program for the transmission and control of onchocerciasis

Abstract

ONCHOSIM is a computer program for modelling the transmission and control of the tropical parasitic disease onchocerciasis, or river blindness. It is developed in collaboration with the Onchocerciasis Control Programme in West Africa (OCP), and is used as a tool in the evaluation and planning of control operations. The model comprises a detailed description of the life history of the parasite Onchocerca volvulus and of its transmission from person to person by Simulium flies. The effects of different control strategies, based on larvicide application and chemotherapy (ivermectin), on the transmission and on the disease symptoms can be evaluated and predicted. In the program two simulation techniques are mixed. Stochastic microsimulation is used to calculate the life events of individual persons and inhabitant parasites, while the dynamics of the Simulium population and the development of the parasite in the flies are simulated deterministically. Output of ONCHOSIM conforms to the format in which data collected by the OCP are reported. This enables detailed checking of model specifications against empirical data. Output can also consist of summarizing key indices for the intensity of onchocerciasis infection, which is especially useful for comparing the effectivity of control strategies.

Human infection patterns and heterogeneous exposure in river blindness

“…Most models focus on onchocerciasis in West Africa (13)(14)(15)(16)(17), with some models focusing on Latin America (19), but few attempt to bring epidemiological commonalities and differences into a single and coherent mathematical framework (29). Age-specific exposure to vector bites (13)(14)(15)(16), operation of parasite-related human mortality (13,15), and parasite-induced immunosuppression (12,17,26) are among the mechanisms put forward to explain observed departures Observations of ABR and L3 load are independent from the data to which the model has been fitted. of O. volvulus patterns from predictions generated by simple immigration-death models (7).…”

“…Although some age-dependency in exposure is assumed in epidemiological models (13)(14)(15)(16), infection-facilitated parasite establishment has been proposed as another explanation for increasing age-intensity profiles (17). However, differences in infection between males and females can be as significant as those among age groups (18)(19)(20).…”

Special agents offer modeling upgrade

“…Perhaps the first successful effort to do agent-based modeling of human societies was SOCSIM (Social Simulation), a program developed in the 1970s by the late English historian Peter Laslett and his coworkers (3). And a pioneering application of agent-based ideas to disease control was ONCHOSIM, a model devised in the late 1980s to help health officials in Africa control the parasitic worm responsible for onchocerciasis or river blindness (4).…”

Towards a comprehensive simulation model of malaria epidemiology and control

“…Micro-simulations of infectious disease control can reproduce arbitrary aspects of interventions such as delivery to selected groups of individuals, and also look at the implications of monitoring selected population subgroups, such as specific age groups or only those with clinical symptoms. Despite this potential, micro-simulations of human parasitic diseases have so far had little impact on public health policy, with the notable exception of the ONCHOSIM model (Plaisier et al 1990 ;Habbema et al 1992), which has proved an invaluable decision support tool in the Onchocerciasis Control Programme in West Africa.…”