Page 456 - The Veterinary Laboratory and Field Manual 3rd Edition

Epidemiology 393

role of veterinary paraprofessionals The animal health service provider then for-
in animal disease surveillance wards this report, based on clinical suspicion of
systems in developing countries a disease, to the nearest veterinary authority. In
this respect, the report of the suspected disease
Animal disease surveillance involves the use of occurrence is ‘passive’ since it was volunteered
various tools to determine the presence, absence by the livestock keeper, or his animal health ser-
or distribution of disease or infection within a vice provider, in the first instance. Normally, if
defined animal population or detecting as early such a report is likely to be a notifiable disease,
as possible exotic or emerging diseases. The type the suspected case or outbreak would result in
of surveillance applied depends on the informa- the conduct of an outbreak investigation, dur-
tion needed to support decision making. Animal ing which laboratory samples would be collected
disease surveillance is also used to monitor dis- and submitted for laboratory testing to con-
ease trends, to facilitate the control of disease or firm, or otherwise, the existence of a notifiable
infection, to provide data for use in risk analysis, disease.
for animal or public health purposes, and to jus- For a country to be in a position to report its
tify investment in disease prevention and control animal health status accurately it needs to estab-
measures. lish systems to detect, report and confirm, by
laboratory diagnosis, all suspected notifiable dis-
ease events at the time that, or very soon after,
Active disease surveillance
they occur. Such systems involve early detection
Active disease surveillance can involve the of suspected disease occurrences, relying largely
deployment of veterinarians and/or veterinary on passive disease surveillance, an effective
paraprofessionals in the field who visit and communication network, trained personnel to
interact with individual or groups of livestock perform outbreak investigations and support-
keepers in order to obtain disease information. ing veterinary diagnostic laboratory services at
The aim of the exercise is to seek information on local through to national levels. Building such
the presence or absence of one or more specific disease surveillance networks can be very chal-
diseases within a defined population of ani- lenging, especially in countries where resources
mals in a defined location at a particular point are limited and where livestock production
in time, using methods of enquiry derived from systems tend to be more extensive. In such situ-
participatory rural appraisal (PRA). Active dis- ations, effective disease surveillance networks
ease surveillance can also involve the collection can be built in parallel with the establishment
of laboratory samples, usually blood/serum, to of animal health service delivery systems. An
detect antibodies against specific disease agents, understanding of the socio-economic and geo-
either due to infection or sometimes to confirm physical factors that determine the various types
sero-conversion following vaccination. of livestock production system is thus important
when developing animal health services and
disease surveillance systems.
Passive disease surveillance
In most developing countries livestock pro-
Passive disease surveillance, in contrast, relies, duction systems can vary from being, at the
in the first instance, on the report of the occur- one extreme, fully commercial, intensive (usu-
rence of a suspected outbreak or case of a disease ally poultry, pig or dairy) production systems,
to a veterinary service provider by a livestock through the middle range of semi-commercial
keeper on his farm or in his neighbourhood. and smallholder mixed livestock/crop farming

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