You wake up sweating, your body sore for no clear reason. A quick check with the thermometer confirms a fever, and you can feel the beginnings of a sore throat. You’re getting sick, that’s for sure, but what exactly is wrong? Modern medicine tells us such general symptoms could signal many ailments — a flu, strep throat, even malaria. Though they may manifest with similar symptoms, these conditions are all very different in how they infiltrate your body and how they’re effectively banished. Take a look at the difference between bacteria, viruses, and parasites to find the best course of action for each.


When you fall sick in a developed country, chances are your ailment is either bacterial or viral. Bacteria are everywhere — on countertops, doorknobs, even inside us. Actually, most bacteria are helpful, or at least harmless, but it’s the one percent minority of troublemakers that comes to mind when someone mentions these microorganisms. Bacteria are single-celled, can reproduce outside of a host, and are capable of thriving in many types of environments. The pathogenic bacteria capable of making us sick can cause a wide range of nasty symptoms and, left untreated, are more than capable of killing us. Luckily, however, we have a powerful tool on our side: antibiotics.

These drugs, which revolutionized medicine in the 20th century, have become both a blessing and a curse. Together with vaccination, antibiotics almost wiped out diseases like tuberculosis in the developed world. This success, however, lead to many misconceptions about antibiotics, the most damaging of which is that antibiotics are effective against any microbe, including viruses. This isn’t the case, but it hasn’t stopped patients from requesting antibiotics when their illness doesn’t go away, or doctors from prescribing them incorrectly. A combination of overprescription and antibiotic use in animals has created a new kind of epidemic: antibiotic-resistant bacteria.


Perhaps the most mysterious of all pathogens, viruses inhabit a unique space in the living world. Described as “organisms at the edge of life,” viruses exhibit a combination of characteristics that has baffled scientists trying to categorize them. On one hand, viruses possess genes, evolve through natural selection, and are capable of reproduction. On the other, viruses do not have a cellular structure or their own metabolism, and require a host cell to replicate. Regardless of whether they fit our definition of life, viruses can wreak havoc on a variety of cells in the human body: Some attack the blood, some go for the respiratory system, some target the liver, and so on.

Many times, viral symptoms are similar to those caused by bacterial infections, but this doesn’t mean the same drugs can effectively treat both. Antibiotics are not effective against viruses in any way. Many public health organizations now caution against prescribing antibiotics until a clinician is certain a patient has a bacterial infection. Vaccines can help prevent viruses, but the treatment of viral infections has remained challenging. We have drugs that can slow down a viruses’ progression and drugs that can ease symptoms, but many times the defeat of a virus rests with our body’s own immune system.

Like bacteria, viruses can be transferred through pretty much anything: surfaces, microbes in the air, bodily fluids. This is not to say all viruses are transmitted through all avenues, though. For example, Ebola can only be contracted through direct contact with bodily fluids from an infected person.



Sometimes we hear people describe other humans as parasitic, and they likely mean that person constantly relies on and exploits others for their own livelihood. It’s a good descriptor — parasitic microorganisms do just that, but in a biological rather than social way. Parasites need a host to survive, using this other living thing for shelter and food. Many parasites don’t negatively affect their hosts, but a handful can produce toxins that make the host sick. Parasites can encompass certain types of bacteria and viruses; all viruses exhibit parasitic characteristics, but due to their dodgy status as only quasi-alive, they are not often considered parasites.

Today, parasitic infections are a large problem in rural, developing areas of the world due to poor sanitation and unhygienic practices. Many neglected tropical diseases, which suffer from lack of attention in the public health world, are parasitic. Water and food contaminated with sewage is the most common way for the cells to infect new hosts. Parasites can also be transferred through food that has been mishandled or undercooked, and insects that act as carriers, transmitting the parasite while they feed on a host.

A parasitic presence can be diagnosed through a fecal exam or a blood test. In especially aggressive cases, X-rays or MRIs may be able to identify parasites in the body. Depending on the nature of the parasite, antibiotics or other medication may be used to treat the infection. Unfortunately, some parasites have no treatment.