Asymptomatic Carriers - What You Don't See - While the term “asymptomatic carrier” made headlines with regard to the SARS-CoV2 virus that causes COVID-19, the concept is actually nothing new to epidemiologists and other researchers who study a variety of diseases in humans and animals. Asymptomatic carriers play critical roles in the transmission of infectious diseases in humans, horses, and other species, but they largely go undetected, thereby hampering control efforts.