Infectious Diseases

An antibiotic does nothing for a cold, influenza or COVID-19. For most people the treatment for a viral respiratory infection is rest, fluids and time.

Shortening that time, easing the cough, settling the fever and helping someone sleep are the goals plants have the longest record with. Elderberry, echinacea and andrographis have been tested in human trials for exactly these jobs.

The mucous membranes are the other natural fit. A gargle, a steam or a topical antiseptic puts the herb directly on the infected tissue, at a concentration swallowing it could never reach.

Most of the evidence behind antimicrobial herbs is laboratory work. It measures what concentration kills an organism in a dish, usually milligrams per millilitre — a level no oral dose can reach in the blood.

The word also covers three different mechanisms. A herb can kill the organism, stop it sticking to a cell wall so it gets flushed out, or make an existing antibiotic work again. Cranberry against bladder infection is the second kind, not the first.

A tapeworm needs a specific antiparasitic drug. Chlamydia needs antibiotics. Measles is prevented by vaccination and managed with supportive care.

No plant changes any of that. For these diseases the history, the biology and the conventional treatment are the whole story.

Malaria is the one infectious disease where plant medicine changed the world twice. Cinchona bark gave the world quinine. Sweet wormwood — qinghao, used in Chinese medicine for fevers for centuries — gave it artemisinin and the combination therapies that are still the front line.

The herb itself is no substitute for the drug. Artemisinin taken as a tea reaches the parasite at too low a dose to clear it, and repeated low doses breed resistance to the medicine that treats malaria everywhere.

• All conditions — every disease, infectious or not, filterable by type.
• Antimicrobial herbs — with the narrower antiviral and antibacterial lists beneath it.
• The immune system — how herbs act on immunity itself.