Germs are formally called microbes, or micro-organisms, which mean “tiny living things you can only see with a microscope.” Most germs are harmless, but some cause disease (infections). Our noses, and also the entire gastrointestinal tube that runs from mouth and throat to esophagus, stomach, bowel, and rectum, are full of germs. These bacteria only cause problems if they wind up in the wrong place, like kidney, lung, brain, blood, etc.
The main categories of germs, from smallest to largest, are:
1. Viruses. These can’t be seen by microscope, only by a special electron microscope. There’s a common expression, “It’s just a virus,” because viruses cause common minor illnesses that get better by themselves, like colds, the flu, and diarrhea. But other viruses aren’t so minor, like HIV, Rabies, Covid, Ebola, Zika, Herpes, Hepatitis, and countless more.
Viruses are hard to grow in culture. We diagnose them mainly by blood tests, often for antibodies that the body makes to attack them. For example, the HIV antibody isn’t effective enough to destroy the virus, but if we find it in the blood, we know the person has HIV (since otherwise the body wouldn’t produce an antibody for it). Expensive tests called PCR can detect viral genetic material (DNA or RNA), to diagnose viral infection. This is what’s used for Covid-19.
Antibiotics don’t work for viruses. For some viruses, there are anti-viral medications to keep them under control, like HIV, Herpes, and Hepatitis B. Hepatitis C virus can indeed be cured now. Most importantly, a number of viral illnesses can be prevented by vaccination.
2. Bacteria. Most can be seen by a simple microscope, and can by cultured in a laboratory. They cause a variety of infections — from simple ones like ear infections, Strep throat, sinusitis, skin boils, and urinary tract infections (UTI’s), to the life-threatening such as pneumonia, meningitis, appendicitis, and sepsis (“blood poisoning”), among others.
Some common bacteria include Staphylococcus (Staph), Streptococcus (Strep), and Escherichia coli (E. coli). Famous ones include tuberculosis, typhoid, cholera, anthrax, botulism, etc. Curable STDs like gonorrhea, chlamydia, and syphilis are also bacteria.
Antibiotics kill bacteria. They’ve increased our life spans since the first sulfonamides (“sulfa drugs”) were invented in 1935, then penicillin in 1945. But the problem is, that bacteria can develop resistance to antibiotics, after which they no longer work. This is happening more and more, due to overuse (like prescribing them for what winds up being a virus), and from adding them to animal feed. We’re on the verge of having pan-resistant strains of some common bacteria emerge, resistant to everything.
3. Protozoa. One-celled animals, also visible by normal microscopes. Sometimes they’re called parasites, but are much different from Helminths [see below]. The main ones causing disease in the US are giardia (diarrhea), trichomonas (vaginitis), and cryptosporidium (community outbreaks of diarrhea). In other countries, or travelers returning from them, the common ones are ameba (amebic dysentery), plasmodium (malaria), Trypanosoma (“sleeping sickness” causing coma in Africa, Chagas Disease causing heart failure or huge intestinal swelling in Latin America). Toxoplasmosis (from cats) can cause brain infections in AIDS, and serious disease in neonates.
Diagnosis can be made by microscope, blood tests, or other tests depending on the germ. We can cure most protozoal illnesses with specific medications that only work for them, not for bacteria (usually).
4. Fungi (plural for fungus). Superficial fungal infections include Yeast (Candida) in the vagina, the diaper area, or on the skin (“intertrigo”: thick red irritation where skin touches skin, like under breasts or the belt line). There are also dermatophyte species, called Tinea, occurring between toes (“athlete’s foot”), in the groin (“jock itch”), or round patches anywhere on the body (“ringworm”), or rarely on a child’s scalp. Yeast & Tinea itch. They’re common, but anyone who gets yeast over & over should get tests for diabetes & HIV (which make yeast easier to grow).
Then there are environmental fungal lung infections, that are often unnoticed, or mild & get better on their own. They include Coccidioidomycosis in especially California & Arizona (“Valley Fever”), Histoplasmosis & Blastomycosis in the Midwest. They’re most dangerous for people with weak immune systems (immunocompromised), like AIDS, when they can spread all over. Deep fungal infections of the blood or brain are also dangerous & occur almost only in the immunocompromised.
There are specific types of antibiotics that work against fungi, and not other germs. These medications are called anti-fungals (duh). They come in creams for the skin, sometimes in pills, & as intravenous (I.V.) administration for serious diseases.
5. Helminths (Worms). Also called parasites, these are not very common in the U.S., but extremely common throughout the 3rd World. Some are big enough to be seen, like Ascaris (roundworm) which can clump to clog the intestines & gallbladder (& even crawl up the throat & out the nose). Tapeworms can grow 50 feet long & live inside your intestine for decades, but only cause harm when microscopic larva (from undercooked beef or pork) wind up in the brain (called cysticercosis).
Schistosomiasis from snails (if you swim in fresh water) gradually destroys livers in Africa and bladders in Asia. Onchocerciasis is “river blindness” in Africa, where worms destroy the eyes. Hookworm, from walking barefoot, enters through skin & works its way to the intestine, causes chronic anemia by sucking blood from the bowel. Guinea worm (Dracunculiasis) from bad drinking water in Africa winds up trying to crawl out the skin, causing severe pain, as sufferers wrap its head around a twig & gradually curling it out over weeks.
There are more, but that’s enough for now. Diagnosis may be made by seeing the worm, or finding eggs by microscope, or by blood tests. There are various medications to treat some Helminths, but others can only be cured early on during infection, although symptoms may not occur until it’s too late. Each worm is different.