Common Infectious Diseases

By: Dzhingarov

Microorganisms are responsible for many infectious diseases, wreaking havoc by invading cells and changing them without being noticed, leading to fever, rash and diarrhea in their wake.

Infections may spread by skin contact, inhaling airborne microorganisms, eating or drinking contaminated food or water, using fomites (door handles, keyboards and razor blades), birth canal transmission or through bites from animals bitten or wounding humans.


Viral agents, also known as viruses, are microbes that cause infectious diseases in their hosts. Each virus consists of small pieces of genetic material encased within a protein- and lipid-based envelope to protect itself from immune systems in its host cell or its own. Viral organisms come in all shapes, sizes, and structures – from being spherical or rod-shaped like bacteria all the way to long cylinders like those seen with Rhabdoviruses – making their existence hard to predict and detect.

Viral infections may spread directly between individuals through fecal or oral transmission, through fomites (surfaces that harbor germs such as doorknobs and countertops), airborne or droplet transmission, coughing or sneezing and inhalation of particles by coughing/sneezing; airborne transmission; coughing or sneezing and inhaling particles into their lungs and airborne transmission by coughing or sneezing and inhalation, coughing/sneezing; or through airborne/droplet transmission – with particles being inhaled into their lungs by coughing/sneezing or cough/sneezing particles entering into their lungs via cough/sneezing particles being inhaled into their lungs; common viral infections include influenza, respiratory infections (rhinovirus and enterovirus), gastrointestinal tract infections (rotavirus & norovirus), and Hepatitis A B C & D respectively.

At any one time, there are trillions of viruses living inside us; only some cause disease in us. Most human disease-causing viruses have names that refer to where or how they were first isolated (e.g. molluscum contagiosum, herpes), their symptoms (hepatitis), or diseases they cause (covid-19).

Viral diseases are transmitted between animals and humans via bites from rats or bites from people; examples include bubonic plague (caused by the Yersinia pestis bacteria) and smallpox (which spreads via Variola virus). Pregnant women can pass infectious diseases to their unborn child through placenta or breast milk during gestation. Germs can linger on inanimate objects, infecting someone when touched later – for instance by handling an infected cat. Fecal or oral exposures are the most prevalent means of transmission; however, other methods may occur as well. Example of such vaccines include the Rotavirus vaccine that protects against Rotavirus infections that cause diarrhea in infants and young children, while Hepatitis A/C virus infections or HIV/AIDS infections cause viremia (the presence of viruses in bloodstream).


Fungi are ubiquitous unicellular eukaryotic organisms found across all environments around the globe, from mushrooms visible to naked eye to yeasts that produce bread-rendering dough. While fungi usually do not cause disease in healthy immune-competent hosts, their pathology can result from accidental penetration of host barriers or immune deficiencies or debilitating conditions which promote their presence and growth.

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Fungus infections can affect any part of the body, but are most frequently found on skin, nails, lungs and internal organs. Fungi reproduce by emitting spores that can be inhaled; similar to seeds in nature they help fungi find suitable locations where they can spread rapidly through airborne contact between individuals.

Fungus infections on the skin typically result in redness, itching and sometimes rashes that can be treated using over-the-counter or prescription medicines. If left untreated, however, mycoses (serious fungal infections) could spread into other parts of the body including organs.

Pulmonary mycoses, or infections caused by fungi that infiltrate the lungs, include Valley fever, Histoplasmosis and Blastomycosis. Unfortunately, these infections are often misdiagnosed as pneumonia or other common illnesses due to symptoms that overlap, including fever, chills, cough and fatigue.

Fungi that cause these diseases thrive in damp soil, decomposing plant material and other damp and warm places such as homes or other buildings where moisture exists. They may even grow inside contaminated water supplies or inside specific medical devices.

Fungal infections can range from being mild, such as those affecting only skin or nails, to becoming severe and spreading to various organs in the body and even other countries. Research funded by NIAID is exploring various methods to diagnose and treat serious fungal infections.

Three endemic mycoses can be found throughout the United States near Mississippi and Ohio River valleys, California and Arizona. Their spread may be associated with increasing temperatures or climate changes, drought conditions or increased use of land for agriculture or housing purposes in these areas.


Parasites are tiny organisms or worms with multiple cells that rely on other living things for food and shelter; this dependence often makes their hosts sick. Parasites come in all sizes and forms; from invisible organisms (protozoa) to visible worms that can be seen by the naked eye (helminths). Many parasitic diseases are caused by helminths – flatworms or roundworms found in your digestive tract that can spread disease throughout your body. Hookworms and tapeworms can enter through the skin while others such as schistosomes can infiltrate blood or tissues, infect reproductive organs or eyes and spread from person to person through food and water contamination. Helminths may also infest reproductive organs or eyes before spreading from person to person through food or water contamination. Other parasitic infections include trichomoniasis, giardiasis, cryptosporidiosis and toxoplasmosis – among many more – among many more than those listed above.

These organisms spread via contaminated water, food, dirt or waste. Some, like malaria-causing parasites transmitted by mosquitoes; intestinal parasites (protozoa and helminths), however, spread by person-to-person contact or through contact with feces-contaminated food or water or through contact between people; while cysts such as Enterobius vermicularis (Strongyloides stercoralis) and Entamoeba histolytica do not require intermediate hosts in order for growth or maturity; instead they commonly found in soil or water or passed from mother to fetus during gestation.

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Parasitic infections typically impact the digestive tract; however, some parasites such as schistosomes tend to invade other systems like blood and tissue more commonly. Malaria or parasites infecting lung, brain or eye tissue may spread throughout the body if left unchecked.

Parasite infections can be serious and even life threatening, yet modern medications can effectively treat many forms of parasitic infection, though some side effects may occur. Therefore, it’s essential that patients follow their physician’s orders for treatment, including taking preventative measures like improving sanitation and providing clean drinking water sources – which in turn can reduce prevalence rates of some parasitic diseases. Furthermore, hand washing after using the toilet will lower chances of spreading microscopic parasite eggs through food or water supplies to others.

How do you get an infection?

Some infectious diseases are spread through direct contact between sick individuals, such as kissing, touching or coughing or sneezing; others spread by breathing in bacteria or viruses that have been released into the air when an infected individual breathes out; still others are transmitted via insects such as mosquitoes, fleas, lice and ticks that carry germs between organisms; you could even get an infection by eating or drinking contaminated food or water, coming in contact with infected soil or plants or being exposed to them directly.

When bacteria or other microorganisms enter our bodies, our immune systems respond by sending white blood cells out to fight off an infection. You may experience fever, malaise, headache and rash as your immune system tries to flush the infectious organism out.

Bacterial infections occur when bacteria that normally reside in your mouth, nose or eyes (or other places like cuts) enter unwelcomed parts of your body – such as in a cut). Bacterial infections can be very serious; even life-threatening in severe cases (septsis). Sepsis occurs when your immune response damages its own tissues causing life-threatening drops in blood pressure and organ failure.

Symptoms of bacterial infections vary, depending on their location in the body and type. For instance, infections caused by staphylococcus bacteria typically present as boils or cellulitis in an affected area; others like gonorrhoea or hepatitis B can spread from person to person and need medical treatment right away.

Your doctor can diagnose an infection by listening to your symptoms and conducting a physical exam, while also asking about your medical history and ordering blood tests to look for signs of infection, such as white blood cell counts or antibodies, in your blood. Infections that threaten life-threatening conditions, like sepsis, must be immediately treated with antibiotics either orally or intravenously (IV). If sepsis develops further, hospitalization will likely be required in an intensive care unit.