Modelling vector-borne and other parasitic diseases - Proceedings of a workshop organized by ILRAD in collaboration with FAO - 23-27 November 1992 Nairobi, Kenya













Table of Contents


HELD AT ILRAD, NAIROBI, KENYA
23-27 NOVEMBER 1992

Edited by
B.D. Perry
J.W. Hansen

THE INTERNATIONAL LABORATORY FOR RESEARCH ON ANIMAL DISEASES
BOX 30709 · NAIROBI · KENYA

The International Laboratory for Research on Animal Diseases (ILRAD) was established in 1973 with a global mandate to develop effective control measures for livestock diseases that seriously limit world food production. ILRAD's research program focuses on animal trypanosomiasis and tick-borne diseases, particularly theileriosis (East Coast fever).

ILRAD is one of 18 centres in a worldwide agricultural research network sponsored by the Consultative Group on International Agricultural Research. In 1993 ILRAD received funding from the African Development Bank, the United Nations Development Programme, the World Bank and the governments of Australia, Belgium, Canada, France, Germany, Ireland, Italy, Japan, the Netherlands, Norway, Sweden, Switzerland, the United Kingdom and the United States of America.

Production Editor: Peter Werehire

Cover illustration: Russ Kruska, Dave Elsworth, Joel Mwaura

This publication was typeset on a microcomputer and the final pages produced on a laser printer at ILRAD, P.O. Box 30709, Nairobi, Kenya, telephone 254 (2) 630743, fax 254 (2) 631499, e-mail BT GOLD TYMNET CGI017. Colour separations for cover were done by PrePress Productions, P.O. Box 41921, Nairobi, Kenya. Printed by English Press Ltd., P.O. Box 30127, Nairobi, Kenya.

Copyright © 1994 by the International Laboratory for Research on Animal Diseases.

ISBN 92-9055-297-2

The correct citation for this book is Modelling Vector-Borne and other Parasitic Diseases: Proceedings of a Workshop Organized by ILRAD in Collaboration with FAO, ILRAD, Nairobi, Kenya, 23-27 November 1992, eds. B.D. Perry and J.W. Hansen. Nairobi: The International Laboratory for Research on Animal Diseases, 1994.

This electronic document has been scanned using optical character recognition (OCR) software and careful manual recorrection. Even if the quality of digitalisation is high, the FAO declines all responsibility for any discrepancies that may exist between the present document and its original printed version.


Table of Contents


Foreword

Opening address

Introduction

The contribution of modelling to our understanding of infectious diseases

Abstract
Introduction
Population versus individual perspective
Quantitative approach
Static evaluation of helminth disease
Dynamic impact on helminth populations of chemotherapy application
Qualitative versus quantitative prediction
Vaccination against childhood viral diseases
Demographic impact of aids
Conclusions
References

The modelling of vector dynamics in disease research

The impact of modelling on animal disease control

Abstract
Introduction
Types of models
Applications of the various modelling approaches
Examples of models
References

ILRAD's research programs and the modelling needs of ILRAD and FAO

The trypanosomiasis program at ILRAD
Modelling needs of the tick-borne diseases program
The socioeconomics program and perceived modelling needs in the areas of epidemiology, socioeconomics and environmental impact assessment
Modelling needs of FAO

Vector and helminth population dynamics

Tsetse vector population dynamics: ILRAD's requirements
Tick vector populations dynamics: ILRAD's requirements
Tsetse population dynamics
Simulation of tick population dynamics

Abstract
Introduction
Simulation approach
Software
Simulation of control
Research needs
References

Modelling of Rhipicephalus appendiculatus population dynamics

Abstract
References

Host density and tick dynamics: The case of the vector of Lyme disease

Abstract
Introduction
The model
Results
Discussion
Acknowledgements
References

Modelling helminth population dynamics

Abstract
Introduction
A brief history of helminth models
The parasitic phase of the life cycle of Fasciola hepatica
The parasitic phase of the life cycle of the common trichostrongylid nematode parasites of cattle and sheep
Other regulatory processes
The significance of parasite frequency distributions
Summary
Acknowledgements
References

Session discussion

Parasite transmission

Transmission of Theileria: ILRAD's requirements
Transmission of trypanosomes: ILRAD's requirements
Models for Leishmania transmission

Abstract
Introduction
Structural deficiencies of the vectorial capacity equation
Difficulties of parameter estimation
Comparative analysis
Absolute estimates of Leishmania transmission rate?
Conclusions
References

The transmission dynamics of Theileria parva

Abstract
Introduction
Description of model
Summary of results
Discussion
References

Spatial factors in the assessment of trypanosomiasis challenge

Abstract
Introduction
Methods
Results
Discussion
Acknowledgements
References

Session discussion

Host-parasite interaction

Possible application of modelling methods to bovine immune responses to Theileria parva
Immune responses and pathogenesis of bovine trypanosomiasis
Modelling of host-parasite interactions and their influence on the course of infection in tolerant and susceptible animals
Potential applications of modelling in the bovine genome project
Use of mathematical modelling for elucidating trypanotolerance: Preliminary considerations

Abstract
Introduction
Conclusions
References

Session discussion

Parasite variations and polymorphism

Parasite polymorphisms: Modelling variations in African trypanosomes
Polymorphisms in Theileria parva
Application of modelling to trypanosomiasis chemotherapy
Models for investigating genetic exchange in protozoan populations

Abstract
Introduction
Quantitative analysis of field populations
Rate of genetic exchange and the evolution of drug resistance: The example of Plasmodium.
Conclusions
References

Modelling anthelmintic resistance

Abstract
The problem
Models of anthelmintic resistance
Implications of models for resistance management
Will models help solve the problem?
Acknowledgements
References

Session discussion

Effect of disease control programs

Modelling vector-borne disease epidemiology and the impact of control programs
Needs for modelling socioeconomic and environmental impacts of livestock disease control
The relationship between infections, diseases and their economic effects

Abstract
The relationship between infection and disease
A systems view of interactions among factors to produce disease
Mechanisms by which disease may alter animal productivity
Effects on ingestion
Effects of disease on feed digestibility
Effects of disease on physiological processes
Measurable effects of diseases on livestock productivity
Effects of disease on herd productivity
Effects on capacity to maintain and improve herd
Effect of disease control measures in productivity of animals
Effects of animal disease on human welfare
Effects of disease on animal welfare
Inclusion of economic effects in a disease model
Conclusion
References

Modelling livestock productivity

Abstract
Pasture production
Model prices
The economic effects of diseases
The effects of risk
Responses to risk
Offtake rules
Initial model values
Results
Prices determined by world market
Prices determined by domestic market
Discussion
Efficiency of offtake rules
Incentive problems
Future research
References

Potential for modelling ecological responses to the control and prevention of disease in African livestock populations

Abstract
Introduction
When technological interventions overcome ecological constraints
Modelling ecological effects in relation to carrying capacity
Ecosystem modelling: needs and capabilities
Modelling interactions between livestock, humans and wildlife
Previous experiences using ecosystems analysis in African livestock and wildlife ecosystems
Conclusions
References

Session discussion

Modelling systems

Modelling: A review of systems and approaches for vector-transmitted and other parasitic diseases in developing countries

Abstract
Introduction
Analytical models
Simulation
Deterministic simulation models
Chemical resistance
Biological indices
Stochastic simulation models
East coast fever modelling
Weather characterization
Tools for simulation
Benefits of simulation
Data models
Information models
References

Modelling disease on a geographical surface

Abstract
Introduction
Mechanisms of representing spatial aspects within a model
Example models
Potential application to African trypanosomiasis
Reference

Statistical modelling of georeferenced data: Mapping tsetse distributions in Zimbabwe using climate and vegetation data

Abstract
Introduction
Sources of data
Results
Discussion
Acknowledgements
References

Application of modelling

The development and application of models in the planning and implementation of reduced and strategic-minimal tick-control strategies in Zimbabwe

Abstract
Introduction
Data used for modelling
Tick-control zones
Modelling tick-control strategies
Planning and implementing control strategies
Effects of alternate dipping strategies on the control of ticks and tick-borne diseases
Discussion
Acknowledgements
References

Practical experiences in using models for tick control in Malawi
Application of models to screwworm eradication programs

Abstract
Introduction
Knipling's model
References

Potential for application of current models for the improvement of helminth control: Advantages, limitations, shortcomings

Abstract
Introduction
Complexity as an obstacle to model building
Model validation
Beta testing
Potential for application of current models
PARABAN
Advantages, limitations, shortcomings
References

Initial practical experiences in using epidemiological modelling in Costa Rica

Abstract
Introduction
Information system
Model 1. The transmission of Tritrichomonas foetus in Costa Rica: An epidemiological simulation model
Model 2. Early calfhood morbidity and mortality in Costa Rican tropical cloud-forest dairy farms: An economical analysis
Model 3. Sero epidemiological studies on anaplasmosis and babesiosis in Costa Rica: Spatial autocorrelation analysis and ecological risk assessment
Conclusion
References

Session discussion

Collection, collation, analysis and dissemination of data on vector-borne and other parasitic diseases

Abstract
Introduction
Collection
Collation
Analysis
Dissemination
References

General discussions and recommendations

Appendix: List of participants

List of participants
Observers