Infectious diseases, also known as communicable diseases, are illnesses caused by a pathogen (a disease-causing organism such as viruses, bacteria, fungi, parasites, etc.) that can be spread from one person to another. Disease spread (aka transmission) can occur directly or indirectly. Direct transmission happens from close contact with an infected person, while indirect transmission may happen through infected water, food, surfaces, or insect bites. Not all bacteria, fungi, etc. cause disease. In fact, many are helpful in the body and in the environment, and some may only cause disease in people with weakened immune systems. There are hundreds of known infectious diseases worldwide, with varying symptoms and causative pathogens. Infectious diseases can be mild or severe/life-threatening, and some are very common, while others are rare. In many cases, untreated infections can cause serious complications and other medical issues. Many infectious diseases, particularly those caused by viruses, will go away on their own, while others require treatment with anti-infective medications. These medications are available as oral medications, intravenous or injectable medications, and topicals such as creams and ointments or ear/eye drops.
Also called “antibiotics,” are used to treat various diseases caused by bacteria. Some examples of bacterial infections include strep throat, tuberculosis, whooping cough, urinary tract infections, skin infections (cellulitis, boils/abscesses), STDs such as syphilis, gonorrhea, and chlamydia, Lyme disease, Typhoid fever, and some types of pneumonia, meningitis, ear infections, sinus infections, and gastrointestinal infections/food poisoning. It is important to remember that many similar infections (ex- ear infections, gastroenteritis, colds/respiratory infections, etc.) may be caused by viruses, and antibiotics will not work to treat those infections. Antibiotics work by killing bacteria or limiting their growth inside the body. They act either by destroying the structure of the bacteria themselves or by interrupting the bacterial growth/reproductive cycle. There are many different types of antibacterial medications, and your healthcare provider will choose the best one for you based on the location and type of infection.
Examples of common antibacterial medications are listed below:
Treat illnesses caused by viruses. Not all viral infections will need treatment with an antiviral medication, as many are self-limiting, meaning they will resolve on their own after a few days. There are fewer antiviral medications available to treat a limited number of viruses than there are antibacterial medications, which treat many more types of bacterial infections. Most antiviral medications do not cure viral infections but can help improve symptoms and decrease the duration of illness. In long-term viral infections, antivirals can help to control the infection and improve quality of life and lengthen life expectancy. Human immunodeficiency virus (HIV) is a clear example of this. Viruses need a host cell, meaning they must multiply inside a human or animal cell to remain infectious and cause disease. Antivirals work by blocking a virus’s entry into cells, interrupting the viral replication/ growth process, or enhancing the immune system to fight the virus. These medications can decrease the viral load/amount of virus in the body, help the virus to become inactive, and help reduce transmission of the virus to others. Examples of illnesses that antivirals are used to treat include HIV, Hepatitis B and C, influenza, genital herpes, human papillomavirus (warts), COVID-19, chicken pox, shingles, Ebola virus, and cytomegalovirus (CMV). There are several combination medications that include more than one of these active ingredients.
Examples of antiviral medications include:
Treat infections causes by fungi. Examples include ringworm, athlete’s foot, vaginal candidiasis (yeast infection), thrush, aspergillosis, pneumocystis pneumonia, candidemia (fungal blood infection), histoplasmosis, Valley fever, and other fungal types of pneumonia, eye infections, meningitis, skin infections. Some of these infections are common and easily treated, while others can be very serious, especially in patients who have compromised immune systems. Antifungal medications work by limiting fungal growth, or by destroying fungal cells.
Examples of antifungal medications include:
Treat infections caused by parasites. Parasites are small organisms that use a host, such as the human body, to survive. Examples of parasitic infections include several illnesses caused by insect bites, such as malaria, Yellow Fever, Dengue Fever, Valley Fever, Leishmaniasis, and trypanosomiasis, as well as those caused by parasitic worms- pinworms, roundworms, hookworms, trichomoniasis (an STD), toxoplasmosis, and some gastrointestinal infections such as giardiasis and cryptosporidiosis. These parasitic worms are found naturally in the environment and may be acquired through the skin or through ingesting infected food or water. Infections with hair and body lice and scabies are also considered parasitic infections. Antiparasitic medications work by killing the parasite and/or its eggs, stopping the parasite from attaching to the body’s tissues, or stopping growth of the parasite. Some antibacterial drugs also have antiparasitic properties and are used to treat these infections.
Examples of antiparasitic medications include:
Common side effects that you may experience while taking anti-infective medications include:
There are several possible serious side effects with anti-infective medications, but they are rare and usually related to a long duration of treatment. These will be discussed below.
Clostridium difficile (C. diff) infection is an overgrowth of “bad” bacteria in the gut due to the “good” bacteria being killed by antibiotic use. It can cause severe, sometimes bloody, diarrhoea that can lead to dehydration, and is very contagious. If you experience frequent and/or bloody diarrhoea while taking antimicrobial medications, you need to seek medical attention right away.
Allergic Reactions are possible with any medication, and the risk is slightly increased with anti-infective medications. However, they are still rare. In some cases, they may be life-threatening, though. Signs and symptoms of allergic reactions include rash, hives, swelling, itching, shortness of breath, or a sensation of tightness in the throat or chest, and may be accompanied by nausea and vomiting. Seek medical attention if you experience these symptoms while taking these medications. If shortness of breath or chest tightness/throat swelling is present, this is an emergency that needs immediate medical attention.
Central Nervous System Effects that may occur, rarely, while taking these medications include numbness and tingling in the hands and feet, nerve damage, and seizures. While these are rare, some may be permanent and may require discontinuation of the medication and extra medical treatment.
Organ Damage, especially to the liver or kidneys, is possible with several anti-infective medications. Signs and symptoms of organ damage include decreased urination, abdominal pain, and yellowing of the skin or whites of the eyes. If you have a serious infection that requires long-term treatment, it is important to keep all medical appointments and have regular blood draws, which can often detect abnormal lab values that indicate organ damage before symptoms occur.
Blood count abnormalities such as low red or white blood cells or platelets are possible with several medications. If you have abnormal or unexplained bruising, easy bleeding, or a cut that takes an unusually long time to stop bleeding, seek medical attention. These blood abnormalities may also be detected with regular blood draws during long-term treatment.
Antimicrobial Resistance is a process that many pathogens can undergo, usually genetic mutations, that help them become more difficult to kill with anti-infective medications. If you have an infection that does not seem to be getting better after a few days of treatment, notify your doctor, because you may need stronger medication to treat your infection effectively. It is also important to complete the entire course of medication as prescribed to help prevent antimicrobial resistance.
Drug Interactions are common with many anti-infectives. Some can be severe and require a change in medication therapy, so it is important that your prescriber and pharmacist know all medications you are taking.
Many infectious diseases can be prevented with proper infection control measures. It is important to practice good hygiene, wash your hands frequently, use safe food preparation practices, and practice safe sex. You should also avoid close contact with anyone you know that is sick and consider wearing a mask in public during periods of high respiratory disease cases, including influenza and COVID-19. There are also vaccines available that can help prevent many infectious diseases. Talk to your healthcare provider about vaccines that may be available to you.