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Prev Vet Med. 2016 Mar 1;125:135-46. doi: 10.1016/j.prevetmed.2016.01.001. Epub 2016 Jan 6.

Area contact networks and the spatio-temporal spread of infectious salmon anemia virus (ISAV) in Chile.

Author information

1
USDA APHIS VS Centers for Epidemiology and Animal Health, Surveillance Design and Analysis, 2150 Centre Ave, Fort Collins, CO 80526-8117, United States. Electronic address: lori.l.gustafson@aphis.usda.gov.
2
USDA APHIS VS Centers for Epidemiology and Animal Health, Surveillance Design and Analysis, 2150 Centre Ave, Fort Collins, CO 80526-8117, United States.
3
Sernapesca, Chile's National Fisheries and Aquaculture Service, Victoria 2832, Valparaiso, Chile.
4
SalmonChile, Department of Fish Health, Instituto Tecnologico del Salmon, Av. Juan Soler Manfredini 41, OF 1802 Puerto Montt, Chile.
5
Instituto de Medicina Preventiva Veterinaria Facultad de Ciencias Veterinarias Universidad Austral de Chile Campus Isla Teja s/n, Valdivia, Chile.
6
Lab de Biotecnologia y Patologia Acuatica Facultad de Ciencias Veterinarias Universidad Austral de Chile Campus Isla Teja s/n, Valdivia, Chile.
7
Colorado Department of Public Health and Environment, 4300 Cherry Creek Drive South, Denver, CO 80246, United States.

Abstract

Area management, the coordination of production and biosecurity practices across neighboring farms, is an important disease control strategy in aquaculture. Area management in aquaculture escalated in prominence in response to outbreaks of infectious salmon anemia (ISA) internationally. Successes in disease control have been attributed to the separation achieved through area-level synchronized stocking, fallowing, movement restrictions, and fomite or pest control. Area management, however, is costly; often demanding extra biosecurity, lengthy or inconveniently timed fallows, and localization of equipment, personnel, and services. Yet, this higher-order organizational structure has received limited epidemiologic attention. Chile's National Fisheries and Aquaculture Service instigated area management practices in response to the 2007 emergence of ISA virus (ISAV). Longitudinal data simultaneously collected allowed retrospective evaluation of the impact of component tenets on virus control. Spatiotemporal analyses identified hydrographic linkages, shared ports, and fish transfers from areas with recent occurrence of ISAV as the strongest predictors of virus spread between areas, though specifics varied by ISAV type (here categorized as HPR0 for the non-virulent genotypes, and HPRv otherwise). Hydrographic linkages were most predictive in the period before implementation of enhanced biosecurity and fallowing regulations, suggesting that viral load can impact spread dynamics. HPR0 arose late in the study period, so few HPRv events were available by which to explore the hypothesis of HPR0 as progenitor of outbreaks. However, spatiotemporal patterns in HPRv occurrence were predictive of subsequent patterns in HPR0 detection, suggesting a parallel, or dependent, means of spread. Better data precision, breadth and consistency, common challenges for retrospective studies, could improve model fit; and, for HPR0, specification of diagnostic test accuracy would improve interpretation.

KEYWORDS:

Bay management; Epidemiology; Fish health; Infectious salmon anaemia; Spatiotemporal analysis

PMID:
26774449
DOI:
10.1016/j.prevetmed.2016.01.001
[Indexed for MEDLINE]

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