Microorganisms or germs? What causes infections?
Infections are common. From ear infections and the flu to COVID-19, we all have had at least one. Viral, bacterial, fungal, and parasitic infections all have different impacts on the human body based on the strength and resilience of the immune system.
Viruses, bacteria, and parasites are living organisms found all around us. They are in water and soil. They are on the surfaces of foods that we eat. They are also on surfaces we touch, such as countertops in the bathroom or kitchen. Some bacteria live in and on our bodies and don’t cause problems.
Four Main Types of Infections
Infection occurs when germs enter your body and multiply, resulting in disease. There are four main types of infections:
- Viral
- Bacterial
- Fungal
- Parasitic
In response to an infection, the immune system goes into overdrive, activating white blood cells and antibodies to fight the foreign invader. This can cause symptoms such as fever, headache, and rash.
1. Viral infection
Viruses can cause a wide range of infectious diseases. Viruses cause illness by killing cells or interfering with cell function.
The virus infiltrates a host's body and attaches itself to a cell, where it releases its genetic material. The virus multiplies as the cell replicates. When a cell dies, more viruses are released, infecting new cells. Some viruses alter the function of cells rather than killing them.
Bodies frequently respond by inducing fever (heat inactivates many viruses), secreting a chemical called interferon (which prevents viruses from reproducing), or mobilizing the immune system's antibodies and other cells to target the invader.
Most viral diseases are self-limiting, and the immune system may be able to fight them off. In rare cases, doctors may prescribe antiviral medications. Vaccinations can also help fight viral diseases.
2. Bacterial infection
Bacteria cause a wide range of infectious diseases, including strep throat and urinary tract infections, meningitis, and tuberculosis. Bacteria are also to blame for many skin rashes.
Bacteria can enter the body through wounds, scrapes, surgical incisions, and the mouth and nose. Some bacteria proliferate so quickly that they crowd host tissues and disrupt normal function. Some may kill cells and tissues right after they multiply. Sometimes, these produce toxins that can paralyze, destroy cells or trigger a massive immune response that is toxic.
Antibiotics are the first-line defense against bacterial infections.
3. Fungal infection
Fungal infections are often more bothersome than dangerous. However, some can cause serious illness.
Inhaling fungal spores is one of the most common ways for an internal fungal infection to develop. Fungal spores are frequently found in decaying vegetation or animal feces.
Fungal cells can invade healthy tissues and disrupt their function. The body often launches an immune response against fungal particles, which causes collateral damage to the cells.
Infected people are treated with a combination of antibiotics and antifungal medications.
4. Parasitic infection
Protozoa are a type of parasite that thrive on moisture and frequently spread disease via water. Some protozoa cause intestinal infections, resulting in diarrhea, nausea, and stomach upset.
In healthy people, parasites cause mild illness, but those with severely weakened immune systems can develop serious infections that can spread to major organs.
Oral rehydration therapy is usually the first-line treatment. Antiparasitic drugs with a broad spectrum of action can be used to treat severe cases.
What are other types of infection?
- Endogenous: Infection that develops within the body due to organisms already present in the body.
- Example: bacterial vaginosis
- Exogenous: Infection that starts outside the body, caused by foods, fluids, fomites, etc.
- Example: food poisoning due to contaminated food
- Nosocomial: Hospital-acquired infection that is typically resistant to antibiotics
- Example: sepsis due to methicillin-resistant Staphylococcus aureus
- Opportunistic: Infection that occurs when the body's defenses are compromised (acquired immune deficiency syndrome, cancer, diabetes).
- Examples: Kaposi's sarcoma and Clostridioides difficile diarrhea