Diseases caused by microorganisms in humans are known as pathogenic diseases. The word pathogen is derived from a Greek word that means 'giving rise to suffering'. These diseases can be caused by a number of agents like bacteria, viruses, fungi, etc. All these pathogenic agents can lead to a variety of diseases and conditions. There are many good bacteria that live on and within the human body systems. These good bacteria help our immune system keep away pathogenic bacteria. Many people often ask 'is a bacterial infection contagious'? Yes, such infections are contagious. There exist hundreds of bacterial diseases affecting humans all over the globe. When the immune system and the beneficial bacteria are affected in some way, pathogenic bacteria can easily attack the body, interrupt normal body processes, and can cause diseases. Such infections are known as opportunistic infections. Bacteria can cause food poisoning, tooth decay, anthrax, pneumonia, etc. A few bacteria have even been linked with cancer. Chronic Helicobacter pylori (H. pylori) infection can lead to stomach ulcers and cancer over time. Women with Chlamydia trachomatis infection of the reproductive organs have a greater risk of developing cervical cancer than other healthy women. ➺ The main source of pathogenic bacteria is raw food such as meat, poultry, egg, dairy products, etc. ➺ The other sources of pathogenic bacteria are pests and pets. Pests like cockroaches, rats, mice, etc. are carriers of bacteria. Pets that are infected with fleas and ticks also cause diseases in humans due to flea or tick bites. ➺ The third source of pathogenic bacteria are people. People can pass on infection by sharing food, utensils, clothes, even through kissing and sex, through infected body fluids, and respiratory droplets. ➺ The last source of these infectious diseases is through soil. Soil is rich with pathogenic bacteria that can cause poisoning, infection, and even gangrene. You can even find disease-causing bacteria in stagnant water under the coolers, sewage, and uncovered water tanks. This is the reason why you should wash roots, fruits, and vegetables properly. Pathogenesis of a disease is the development of a disease in the infected person. The initial appearance of the disease till its end stage is known as pathogenesis of a disease. It is very important to identify the disease and treat it accordingly. Different steps of a disease include the origin of a disease, the progressive changes occurring in the body, and the action of the disease on the body, as it develops a hold on the body. For example, when a child falls down while playing and develops a cut, the wound gets colonized with Staphylococcus bacteria. The bacteria cause inflammation, and as the bacteria grow, they lead to a full-blown infection. This process of getting a wound till the development of infection is known as pathogenesis. An infection occurs when pathogenic bacteria, viruses, or other microbes enter your body, and start multiplying. Disease occurs when the infection damages certain cells in your body. Then, the signs and symptoms of an illness are noticed. The study of pathogenesis of disease is very important for medical professionals and scientists, as it helps them understand the cause, the changes in the body, and epidemiology. The signs and symptoms help diagnose the disease. They also help design the treatment of the disease. ✦ Common Diseases Caused by Pathogenic Bacteria

• Food poisoning - Escherichia Coli
• Strep throat - Streptococcus pyogenes
• Tuberculosis - Mycobacterium tuberculosis
• Legionnaire's disease - Legionella pneumoniae
• Cholera - Vibrio cholera
• Syphilis - Treponema pallidum
• Gonorrhea - Neisseria gonorrhoeae
• Anthrax - Bacillus anthracis
• Leprosy - Mycobacterium leprae
• Bubonic plague - Yersinia pestis
• Tetanus - Clostridium tetani
• Pneumonia - Streptococcus pneumoniae
• Influenza - Haemophilus influenzae
• Pneumonia - Klebsiella pneumoniae
• Septicemia - Pseudomonas aeruginosa
• Respiratory Tract Infections - Moraxella catarrhalis
• Pneumonia - Chlamydophila pneumoniae
• Cellulitis - Streptococcus or Staphylococcus
• Walking Pneumonia - Mycoplasma pneumoniae
• Pneumonia - Legionella pneumophila
• Whooping Cough - Bordetella pertussis
• Lyme Disease - Borrelia burgdorferi
• Gas gangrene - Clostridium perfringens
• Tularemia - Francisella tularensis

Salmonella infection is quite common in the U.S. Similarly, chickens contaminated with Campylobacter can leave people permanently disabled and paralyzed. Clostridium perfringens, also known as C. perfringens, are bacteria that can be found on raw meat and poultry. Staphylococcus aureus (staph), that's commonly present on the skin, throats, and nostrils of many healthy people and animals, multiplies and produces harmful toxins when it is transferred to food products. Listeria monocytogenes bacteria are found in refrigerated, ready-to-eat foods, such as hot dogs, deli meats, unpasteurized milk and dairy products, and raw or undercooked meat, poultry, and seafood. Food poisoning due to these bacteria can lead to nausea, stomach cramps, vomiting, and diarrhea. The list of pathogenic bacteria contains hundreds of such bacteria. Antibiotics are used to treat bacterial infections. ✦ Common Diseases Caused by Fungi

• A yeast that can cause an infection of the mouth and throat - Candida or Candida albicans
• Ringworm - Tinea barbae or Tinea corporis or Tinea capitis or Tinea cruris
• Athlete's foot - Tinea pedis or Trichophyton mentagrophytes or Trichophyton rubrum

✦ Common Diseases Caused by Viruses Like bacteria, viruses can cause numerous diseases. Here are some examples:

• Influenza - Influenza viruses: A, B, and C
• Pneumonia - Influenza (flu) A and B viruses, Respiratory syncytial virus (RSV), coronaviruses, rhinoviruses, parainfluenza viruses, and adenoviruses, etc.
• AIDS - Human immunodeficiency virus
• Genital herpes - Herpes simplex virus-2 (HSV-2) or the herpes simplex virus-1 (HSV-1)
• Ebola hemorrhagic fever - Ebola virus
• Measles - Paramyxovirus
• Chickenpox - Varicella-zoster virus (VZV)
• Shingles - Varicella-zoster virus (VZV)

Antibiotics do not help lower the symptoms of viral infections. ✦ Common Diseases Caused by Protozoa Protozoa are single-celled organisms that hunt and gather other microbes for food. Many protozoa that live in our digestive tract are harmless. Some cause diseases like:

• Toxoplasmosis - A single-celled parasite called Toxoplasma gondii
• Giardia - The flagellated protozoan Giardia intestinalis (lamblia).
• Malaria - Four different species of the parasite Plasmodium cause malaria in human beings.

✦ Common Diseases Caused by Helminths Relatively larger parasites called Helminths and their eggs can invade human intestines, lungs, livers, skin, or brains. They thrive in an environment where they have a ready supply of food. For example:

• Tapeworms
• Roundworms

Pathogenic diseases can be prevented by maintaining a healthy diet. Proper supply of nutrients helps maintain the health of the immune system. Frequent washing of hands and maintaining proper hygiene can also prevent diseases. This was a little information on diseases caused by bacteria and other pathogens. There are many bacteria that can be our friends, but there is no telling when the opportunistic bacteria can strike and bring us down with a horrible infection. Disclaimer: The information provided in this article is solely for educating the reader. It is not intended to be a substitute for the advice of a medical expert.