Pathogen–host–environment interplay and disease emergence

Engering, Anneke; Hogerwerf, Lenny; Slingenbergh, Jan

e Great Bengal Famine of 1943. Also global fisheries production is undergoing a rapid scaling-up, triggering emergence, spread and persistence of pathogens with novel traits. 73 Examples include the emergence of virulent strains of Flavobacterium columnare, Yersina ruckeri and infectious salmon anemia virus in intensively reared salmon. 66, 78, 79 Ironically, the use of (partially effective) vaccines and antimicrobials to control pathogens in intensive systems (including antibiotics as feed additives for growth purposes) and in human medicine may drive selection of pathogens with increased virulence and antibiotic resistance. 60, [80] [81] [82] Vaccination has possibly increased virulence of Plasmodium, Bordetella pertussis and infectious bursal disease virus. 81, 83, 84 Recently, a vaccine escape variant of Streptococcus pneumoniae was identified that rapidly spread throughout the USA. 85 In particular vaccines reducing pathogen growth, transmission or toxicity could select for increased virulence, in contrast to infectionblocking vaccines. 80 A prime example of antimicrobial resistance affecting animal and human health forms the emergence of extendedspectrum beta-lactamases in Entero-bacteriaceae, conferring drug resistance to various classes of antibiotics. 60 In addition, advancements in biomedical technology can in rare cases lead to the emergence of a pathogen through an unexpected route of transmission. One example is the recent multistate outbreak of fungal meningitis in the USA associated with contaminated steroid injection. 86 Unexpected pathogen transmission through solid organ transplants and blood product transfusions has also been reported, 87 but this concerned isolated cases rather than outbreaks.