SPECIAL REPORT - EPIDEMICS

The onslaught of the invisible

Virus HIV-2. A second AIDS virus isolated at the Pasteur Institute in 1985 from a patient originating in West Africa. Colourised image. © Institut Pasteur
Virus HIV-2. A second AIDS virus isolated at the Pasteur Institute in 1985 from a patient originating in West Africa. Colourised image. © Institut Pasteur
©Gil Corre
©Gil Corre

The blue whale, which can be up to 33 metres in length, is the largest animal on Earth. The wasp parasite Caraphractus cinctus, the smallest known insect, is 200 000 times smaller, with a length of 0.17 millimetres. What do these two animals have in common? They are giants. It is the same for man, all other mammals, birds, insects and all of the other familiar animals. They plentifully populate our visible world, where the small Caraphractus cinctus sits on the cusp. But all species together only constitute a small part of the animal world.

Beyond them starts the ‘real' world of our planet's inhabitants. In comparison to our size, the smallest mite is around 20 000 times smaller; amoebas are smaller by a factor of 100 000, and bacteria are around 2 million times smaller than we are. That's not the end. Viruses, about which there is still debate if they are part of the living world or not, leave bacteria looking like gigantic monsters: Spoutnik, a recently discovered virophage virus (see page 21) is less than 50 nanometres: 40 million times smaller than us.

So much for size. But how many are there? As many as we can imagine: in layers of seabed sediment, a single gram contains on average...1 million viruses. They are everywhere, always and ever-present. A world totally invisible to our eyes, where we have friends, as well as a few particularly vicious enemies, engaged in a never-ending, unequal battle. Did you say small is beautiful?


TOP