A. Field of the Invention
The present invention relates to methods and compositions useful for inhibiting, treating, protecting, or preventing infection by Actinobacillus suis. 
B. Description of the Related Art
Actinobacillus suis has recently emerged as a new threat to the swine industry in the United States. Previously associated with high mortality in “high health” herds, A. suis is now recognized as an important pathogen of conventional herds. It is particularly detrimental to younger animals. Infection results in actinobacillosis and can cause sudden death in both neonate and weaned pigs. Symptoms in weaned pigs include anorexia, fever, cyanosis, congestion of the extremities, respiratory distress, pneumonia, necrotizing pneumonia, persistent cough, skin lesions, and fatal septicemia. Pneumonia, arthritis, septicemic signs, pleurisy, pericarditis, and miliary abscesses are known to occur in finishing pigs. Actinobacillosis also causes metritis and abortion in sows.
The gross pathology of actinobacillosis is characterized by lesions found in lungs, kidney, heart, liver, spleen, intestines and skin; hemorrhages and necrosis; and pneumonic lesions resembling pleuropneumonia. Histopathologically, the disease is characterized by the presence of bacterial thromboemboli with accompanying fibrinohemorrhagic necrosis in the vessels of various tissues; necrotizing bronchopneumonia; and pleuritis. Causes and contributing factors to infection include precipitation by Porcine Reproductive and Respiratory Syndrome (PRRS) infection, teeth clipping, de-tailing, scrubbed knees, and entry via either respiration, cuts, or abrasions.
Actinobacillus suis is an opportunistic, gram-negative, non-motile, aerobic and facultative anaerobic coccobacillus that colonizes the upper respiratory tract. Genotyping of A. suis isolates recovered from clinical cases in the North American swine herds has revealed a limited genetic variability, with only 13 strains being identified among 74 isolates recovered from 29 different herds. The Simpson's diversity index (also known as species diversity index, see Simpson, 1949) for A. suis genotypes is 0.64, meaning that a random isolate has a 64% chance of being included in a unique genotype group using for example BOX-PCR (Simpson, 1949; Versalovic et al, 1991; Oliveira et al, 2007). Compared with H. parasuis, for example, which has a diversity index of 0.93 (Oliveira et al, 2007), A. suis is relatively clonal.
The phenotypic diversity of A. suis is also relatively limited. Only 2 serovars, namely O1 and O2 (Rullo, Papp-Szabo and Michael, 2006), and three capsular types, K1-3, have been described so far. Pathogenicity studies suggest that isolates from serogroup O2 tend to be more virulent than O1 isolates (Slavic, DeLay and Hayes, 2000). Serotyping of A. suis isolates used for autogenous vaccine production also confirms that a higher percentage of O2 isolates were associated with clinical disease compared with O1 isolates (Slavic, Toffner, and Monteiro, 2000). Although some of the A. suis virulence factors are known (e.g. the RTX toxins Apx Ivar. suis and Apx IIvar. suis), the factors that may trigger systemic infection still remain to be defined. Some of these potential factors include lipopolysaccharide (LPS) and capsular polysaccharides (CPS), outer membrane protein A (OmpA), proteases, and iron acquisition.
Currently, there are no commercial vaccines available for the control of A. suis, and most field veterinarians rely on autogenous vaccines and antimicrobial treatments to control disease. The development of a vaccine that will potentially protect against most isolates in the field is desirable; however, necessary data regarding the association between genotype, serovar, toxin, protein profiles, and factors that are involved in the pathogenesis of A. suis infection still remain to be defined. Herein, such data are provided, as well as, vaccines, and their methods of use, against A. suis. 