Infection is the invasion and multiplication of microorganisms such as bacteria,viruses,parasites,or other pathogens that are not normally present within the body,invading the host or making someone ill or diseased.An infection may cause no symptoms and be sub-clinical,or it may cause symptoms and be clinically apparent.An infection may remain localized,or it may spread through the blood or lymphatic vessels to become systemic.Hosts normally fight infections themselves via Infection is the invasion and multiplication of microorganisms such as bacteria, viruses, parasites, or other pathogens that are not normally present within the body, invading the host or making someone ill or diseased. An infection may cause no symptoms and be sub-clinical, or it may cause symptoms and be clinically apparent. An infection may remain localized, or it may spread through the blood or lymphatic vessels to become systemic. Hosts normally fight infections themselves via