This is one of those diseases it's best to keep an eye out for, or rather the insect that carries it, instead of reacting only after several symptoms appear.

Tomato Yellow Leaf Curl Virus (TYLCV)

This disease has already from Florida northward, spread by whiteflies. It can totally wipe out tomato plants.
The virus is not seed-borne. It is only transmitted by the whitefly, Bemisia tabaci, which is commonly found in tropical and sub-tropical regions, and in greenhouses in temperate areas.

....Adult whiteflies look like tiny white moths, about 1Â2 mm in length. They fly when the leaf is disturbed. The light-colored eggs are laid on the leaf undersurface and hatch in about 16 to 38 days depending upon environmental conditions.

The link below describes its symptoms, has great pictures, and suggests controls for it.

Here's the recommended disposal method of infected plants.
# symptomatic plants should be carefully covered by a clear or black plastic bag and tied at the stem at soil line. Cut off the plant below the bag and allow bag with plant and whiteflies to desiccate to death on the soil surface for 1-2 days prior to placing the plant in the trash. Do not cut the plant off or pull it out of the garden and toss it on the compost! The goal is to remove the plant reservoir of virus from the garden and to trap the existing virus-bearing whiteflies so they do not disperse onto other tomatoes.

# If symptomatic plants have no obvious whiteflies on the lower leaf surface, these plants can be cut from the garden and BURIED in the compost.

Here is a link that might be useful: Tomato Yellow Leaf Curl Virus (TYLCV)