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. 2013 Jan 11;44(1):2.
doi: 10.1186/1297-9716-44-2.

Association between transmission rate and disease severity for Actinobacillus pleuropneumoniae infection in pigs

Tijs J Tobias  1 , Annemarie Bouma, Angeline J J M Daemen, Jaap A Wagenaar, Arjan Stegeman, Don Klinkenberg
Affiliations

Association between transmission rate and disease severity for Actinobacillus pleuropneumoniae infection in pigs

Tijs J Tobias et al. Vet Res. .

Abstract

A better understanding of the variation in infectivity and its relation with clinical signs may help to improve measures to control and prevent (clinical) outbreaks of diseases. Here we investigated the role of disease severity on infectivity and transmission of Actinobacillus pleuropneumoniae, a bacterium causing respiratory problems in pig farms. We carried out transmission experiments with 10 pairs of caesarean-derived, colostrum-deprived pigs. In each pair, one pig was inoculated intranasally with 5×10(6) CFUs of A. pleuropneumoniae strain 1536 and housed together with a contact pig. Clinical signs were scored and the course of infection was observed by bacterial examination and qPCR analysis of tonsillar brush and nasal swab samples. In 6 out of 10 pairs transmission to contact pigs was observed, but disease scores in contact infected pigs were low compared to the score in inoculated pigs. Whereas disease score was positively associated with bacterial load in inoculated pigs and bacterial load with the transmission rate, the disease score had a negative association with transmission. These findings indicate that in pigs with equal bacterial load, those with higher clinical scores transmit A. pleuropneumoniae less efficiently. Finally, the correlation between disease score in inoculated pigs and in positive contact pigs was low. Although translation of experimental work towards farm level has limitations, our results suggest that clinical outbreaks of A. pleuropneumoniae are unlikely to be caused only by spread of the pathogen by clinically diseased pigs, but may rather be the result of development of clinical signs in already infected pigs.

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Figures

Figure 1
Figure 1
Course of A. pleuropneumoniae CFUs counts in tonsil and nasal samples in time. Tonsil sample counts are presented as A. pleuropneumoniae log10 (CFUs + 1) and nasal samples are presented as log10 (CFUs + 1.5) to separate them graphically from tonsil samples.
Figure 2
Figure 2
Average Clinical Score (AvgCS) of piglets per pair in time. The course of Average Clinical Score of piglets in time.
Figure 3
Figure 3
Association between bacterial load and average disease score. Association between log10 (CFUs +1) of A. pleuropneumoniae 1536 in nasal and tonsil samples and average clinical score (AvgCS) for I- and C-pigs. Regression lines are based on positive samples.
See this image and copyright information in PMC

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