Echinacea root is the all-American immune system strengthener. It triggers production of white blood cells, interferon, leukocytes, T-cells, and B-lymphocytes, as well as directly inhibiting the growth of most bacteria and viruses. Peter Holmes, author of Energetics of Western Herbs, cites it as being effective against anthrax. Echinacea tincture is my first choice for countering infection. (Capsules and pills of echinacea, if used for lengthy periods, may be counterproductive.) A dose of the tincture is one drop for every pound of body weight. I take this several times a week as a preventative, several times daily when there is active infection.
Usnea, a common lichen, is especially rich in a powerful antibacterial bitter called usnic acid (also usinic acid). I use the tincture of Usnea barbata (a dose is 1-2 dropperfuls), but other lichens show similar immune-enhancing and tonifying properties. There are no side effects reported from use of even large amounts of usnea tincture.
Poke root tincture (Phytolacca americana) kicks the immune system into gear incredibly fast. I've seen chronic infection of many years' standing resolve after only one dose, and acute infection subside in a matter of hours. Poke's effect seems to be focused on the lymphatic and glandular tissues of the throat and chest, making it the perfect counter to inhaled anthrax, which attacks the lymph nodes around the lungs. Poke is a specific against pneumonia and a protector of the lungs. It contains an antibacterial alkaloid and a special antiviral protein. It is magnifies the effects of echinacea and they work wonderfully well together.
Poke root is powerful medicine, in fact, a potential poison, and the dose is very small. One drop of poke tincture may be taken daily for no more than three months as a counter to possible infection. Alkaloids in poke root tincture can accumulate in the kidneys, making extended use risky. Caution: You can feel spacy and out of your body when taking poke, especially at higher doses. The first few times, take it after dinner and stay home so you can judge your reaction.
Siberian ginseng (Eleutherococcus) is widely considered the single most effective immune tonic and adaptogen in the herbal realm. Safe and inexpensive, it helps the immune system respond quickly to infection and mitigates the effects of stress. Astragalus root is also an excellent ally for building powerful immunity. Both, or either, may be taken daily for extended periods with no ill effects. I throw several pieces of these roots in every pot of soup I cook.
Ginseng root (Panax quinquefolius or Panax ginseng) is another exceptional ally for the immune system, especially when there is physical or emotional stress. In any form (tincture, tea, extract) it nourishes production of interferon, phagocytes, antibodies, and killer T-cells. So long as you need ginseng, there's no overdose; if you take it when you don't need it however, it may produce an unpleasant, jittery, speedy sensation.
Garlic has been used to prevent infection for thousands of years; and it still works! No need to upset your stomach (and loved ones) by eating it raw; cooked garlic retains its antibacterial powers, so long as you eat enough of it. During plague times, healers in some areas wore a "bird's beak:" a stiff cone was made of paper or bark, stuffed with garlic and spices (cinnamon, cloves, nutmeg), and tied on over the nose to help prevent contagion. That's a little cumbersome for modern times, but inhaling the aroma of a cup of spicy tea (there are many blends available, or make your own) could help you avoid catching contagious disease.
Medicinal mushrooms are not only immune system tonics, they possess antibacterial properties which make them ideal for preventing anthrax infection, according to expert Paul Stametes. A tincture or strong infusion of any shelf fungus with pores can be used, he says. If you prefer to buy your mushrooms, rather than hunt for them, look for reishii (Ganoderma lucidum) or shiitake (Lentinus edodes). Both are adaptogenic, revitalizing, regenerative, and able to directly suppress infection. Side effects, even from large doses, are rare.