Spread and consequences of secondary infections in cattle affected with foot-and-mouth disease in Karbala province, Iraq

Abstract

Foot-and-mouth disease (FMD) is a highly contagious viral disease caused by aphthovirus belonging to the family of Picornaviridae. Although the primary viral infection is known to cause the typical clinical manifestations, such as fever, salivation, and the formation of vesicles around the mouth, muzzle, teats, and interdigital spaces, the breakage of these vesicles opens the entry for opportunistic microorganisms. The latter can greatly affect the disease outcome, however, neither their spread, nor the species composition diversity among cattle herds in Iraqi have not been adequately documented. Thus, the current study was aimed at isolating and identifying the secondary microbial agents that complicate the foot-and-mouth disease lesions in cattle in Karbala province, Iraq. Following the rules of asepsis, a total of one hundred smear samples were collected from the mouth cavity (n=50) and extremities (n=50) of cows that had been clinically diagnosed with FMD on the basis of the sudden appearance of the disease classical symptoms during its regional outbreak. The microbiological investigation showed a complex polymicrobial community consisting of various opportunistic pathogens that were colonizing as well as infecting the primary viral lesions. Moreover, the isolation of several pathogens from a single lesion was a common phenomenon. Among the isolated bacterial pathogens, both Gram-positive and Gram-negative forms were well represented. Trueperella pyogenes turned out to be the most predominant pathogen (18 % of total isolates). Pasteurella multocida was found to be the second (16 % of total isolates) after T. pyogenes. Notably large percentages of Staphylococcus aureus (14 %), both methicillin-sensitive and methicillin-resistant strains, as well as Escherichia coli (13 %), both commensal and pathogenic strains, were found. Other bacterial pathogens that were significant enough to be mentioned individually were Streptococcus dysgalactiae (7 %), Fusobacterium necrophorum (6 %), Pseudomonas aeruginosa (5 %). Fungal pathogens were found less frequently. They were mostly Candida sp. (5 %), as well as Cryptococcus sp. (3 %). It can be noted from these results that bacterial and fungal complications are not only incidental but also common and significant complications that occur as a result of FMD infection. These secondary infections play a vital role complicating the disease pathogenesis. Thus, this research confirmed the urgent necessity of changing the paradigm in the treatment of FMD cases, introducing integrated and holistic treatment approaches, beyond merely supportive therapy of the viral infection.