 A number of diseases have been related to mass die @-@ offs or declines in populations of amphibians , including " red @-@ leg " disease ( Aeromonas hydrophila ) , Ranavirus ( family Iridoviridae ) , Anuraperkinsus , and chytridiomycosis . It is not entirely clear why these diseases have suddenly begun to affect amphibian populations , but some evidence suggests that these diseases may have been spread by humans , or may be more virulent when combined with other environmental factors . 
