PRRS Compendium Producer Edition - National Pork Board
PRRS Compendium Producer Edition - National Pork Board
PRRS Compendium Producer Edition - National Pork Board
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secretions). The aggressive behavior associated with establishing a social order within a group that<br />
involves slashes or bites in the shoulders, neck, and head and results in the exchange of blood and<br />
saliva and transmission of <strong>PRRS</strong> virus. Indirect transmission by fomites, vectors, or aerosols may also<br />
occur. Of these, transmission via instruments and medications contaminated with body fluids from<br />
<strong>PRRS</strong> virus-infected animals is the most important. This includes instruments used for ear notching, tail<br />
docking, teeth clipping, or tattooing, as well as and needles, syringes, medications, and biologics. Recent<br />
research has shown that flies and mosquitoes are capable of mechanical transmission of <strong>PRRS</strong> virus<br />
under experimental conditions (Otake et al., 2002c, 2002d). Establishing whether <strong>PRRS</strong> virus is an insectborne<br />
disease will require additional experimental and field studies. Aerosol transmission is also still an<br />
open question. Results of pig-to-pig aerosol transmission experiments have been mixed and essential<br />
information (the quantity of virus excreted by pigs and the rate of inactivation of aerosolized virus) is<br />
missing.<br />
The ability of <strong>PRRS</strong> virus to establish persistent infections in animals is the primary challenge to successful<br />
prevention and control programs. Establishing and maintaining herd immunity in the face of persistent<br />
infection is problematic because vaccines that induce long-term protective immunity against heterologous<br />
isolates and eliminate or reduce virus shedding are not yet available. Finally, if elimination is achieved,<br />
herds are vulnerable to re-infection with <strong>PRRS</strong> virus through the introduction of subclinically-infected<br />
animals or by area spread. This scenario is reminiscent of other infectious agents, i.e., classical swine<br />
fever virus (hog cholera) or African swine fever, which have been successfully controlled and/or eliminated<br />
in the past through coordinated regional efforts.<br />
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