Quantification of porcine circovirus type 2 (PCV-2) within- and between-pen transmission in pigs.
PCV-2 within- and between-pen transmission was quantified by estimating the daily transmission rate beta and the basic reproduction ratio (R(0)) using a stochastic SEIR (Susceptible, Exposed, Infectious, Removed) model fitted on experimental data. Within-pen transmission was quantified by using four groups of eight SPF (specific pathogen-free) pigs (four infected and four susceptible pigs having direct contact). Between-pen transmission was studied in two groups of 16 SPF pigs (eight infected and eight susceptible pigs having indirect contact (10 cm distance)). Pigs were monitored twice a week (blood samples) and were tested for PCV-2 antibodies (ELISA test) and viral genome load in sera (real-time PCR). Transmission parameters beta(within) and beta(between) were estimated using a maximum likelihood method and the duration of infectiousness, to compute R(0), was estimated with a parametric survival model. Different assumptions were made to determine the end of infectiousness (seroconversion, seroconversion and decline in viral genome load, permanent infectiousness). R(0[within]) (8.9 (5.1-15.4)) was greater when the end of infectiousness was assumed to be related to both seroconversion and a decline of PCV-2 genome load in sera (average duration of infectiousness = 32 days) compared with only seroconversion as the indicator of recovery (R(0[within]) = 5.5 (3.3-9.0)). Whatever the assumption, between-pen R(0) (0.58 (0.23-1.47)) was always significantly lower than within-pen R(0). Only beta(within) was sensitive to the assumption on end of infectiousness and decreased with increasing duration of infectiousness. These results showed that PCV-2 transmission is influenced by contact structure that appears worth being taken into account in an epidemic model.
Andraud
Mathieu
M
AFSSA-site de Ploufragan, B.P. 53, 22440 Ploufragan, France. m.andraud@afssa.fr
Grasland
Béatrice
B
Durand
Benoît
B
Cariolet
Roland
R
Jestin
André
A
Madec
François
F
Rose
Nicolas
N
D000818:Animals; D018173:Circoviridae Infections / Q000635:transmission / Q000662:veterinary* / Q000821:virology; D017925:Circovirus / Q000145:classification*; D016679:Genome, Viral; D006799:Housing, Animal; D016133:Polymerase Chain Reaction; D013047:Specific Pathogen-Free Organisms; D013552:Swine; D013553:Swine Diseases / Q000635:transmission* / Q000821:virology; D013997:Time Factors; D019562:Viral Load