Lice and mites can and do happen, and it is not always obvious from simply looking at the birds. At times of stress, most health issues can escalate, and shipping, even under the best of circumstances, is stressful. However, a bird that is being shipped should be treated at least a day or two beforehand, regardless of whether issues with bugs are suspected. Now most treatments will not kill eggs, so you would probably have to re-treat a week afterwards, and probably a third time as well to completely break the cycle. But that depends on the particular products used. My preferred method is to bathe in a flea/tick shampoo labeled for cats or dogs. For a really bad infestation you can use human lice shampoo. Make sure to completely rinse the product off; white vinegar in the rinse water helps with this. Dusting needs to be with either a permethrin/pyrethrin or carbaryl based product. Diatomaceous Earth (DE) is useless against an infestation. There is some evidence that it can help prevent them. Note that most of these powders/dusts are very drying to the skin, and that itself could cause itching. You can also use a flea/tick/mite spray formulated for dogs, cats or birds. Lice cannot live long off the birds; mites can, so if you find mites, you will need to thoroughly treat all housing and replace all bedding. For the bird that is still lethargic, keep an eye on its poop. Scrambled or hardboiled eggs are a good plan, and gatorade or pedialyte added to the water. If there is not a rapid improvement, consider treating for coccidiosis and/or worms. Note that wild birds are probably the most common vectors of lice & mites, and even of worms, although earthworks and cockroaches are also important worm vectors.