There are two explanations for this apparent
absence. First, in one report the authors specifically looked for
known human viral pathogens (30), and so they would have missed
the chloroviruses. Second, in three other reports, the samples were
filtered through both 0.45-μm and 0.2-μm filters; the material that
passed through both filters was used to extract DNA. These
researchers were primarily evaluating bacteriophages (7, 8, 31). The
icosahedral-shaped chloroviruses are 190 nm in diameter and have
a 34-nm spike structure protruding from one unique vertex (32).
Therefore, it is likely that ATCV-1 and most chloroviruses would be
trapped on a 0.2-μm filter