[Biology Class Notes] on Infectious Diseases Pdf for EXAM

Infectious diseases are the diseases of microbial pathogens, namely viruses, bacteria, fungi, and parasites. These may be transmittable or non-communicable. They may be spread by plants, humans, or insects. The agents who spread the pathogens or pass them on are called vectors or intermediaries of the disease.

Types of Infection

A disease is a condition that, through hampering body processes, impacts only a portion of the whole body. Infectious or non-infectious diseases, both, can cause illness. In general, non-infectious causes may be internal factors, genetic irregularities, and lifestyle, while infectious diseases are caused by pathogenic microorganisms, which are the agents causing the infection. Certain disorders caused by organisms that live in and on are known as infectious diseases. Organisms like viruses fungi bacteria parasites etc can cause a number of infectious diseases. Infectious diseases can be passed from one person to another; some diseases were also transmitted by other animals or insects.

Causes of infectious diseases

are caused by pathogens invading the body. For, e.g., a particular virus can trigger a viral infection. There are infectious agents all around us, and they come in varying forms and sizes. They may be classified on the basis of certain common features. Some of these are single-celled animals like fungi, bacteria, and viruses. Other multicellular organisms like worms are also known to cause illnesses. Microscopic organisms that are most likely to cause infections are also known as pathogens.

Pathogens

Pathogens are basically disease-causing agents. These include viroid’s, nematodes, prions, arthropods, notably mites and fleas and macro-parasites such as helminths and roundworms. Such diseases arise when an organism invades the cells and tissues of the human body with an infection-causing agent that triggers the reaction of the host tissues to these pathogens, both because of the effects of the pathogen and the toxins it releases. Examples of pathogens are

• Bacteria

• Virus

• Fungi

• Parasites

()

These pathogens can enter our bodies in several different ways such as

• Through the transfer of body fluids

• By inhaling airborne droplets or particles

• Skin contact

• Contact with wastes

• Contaminated food or water

Types of infectious diseases

can be classified on the basis of the causative pathogen. The main types are enlisted and described below.

1. Viral infections- this infectious disease occurs due to viruses. Researchers have found around 5,000 types of viruses to date. In this type of infectious disease, viruses attach themselves to a cell by inviting a host’s body and releasing the genetic material. The virus in the body multiplies when the released material forces the cell to replicate the virus. Viruses are the primary cause of viral infections like the common cold, influenza, and so on. The virus can enter a host’s body and attaches itself to the cell where its genetic material activates, and it begins to replicate itself. The cell replicates, and the virus grows. The infection of cells then releases more viruses that can go on to infect new cells. Few viruses alter cell structure rather than destroy the cells. For example, human papillomavirus, the Epstein Barr virus, causes uncontrollable cell replication leading to cancer. Other Examples- polio, dengue, fever, HIV  Zika virus, Ebola virus, Coronavirus swine flu etc

2. Bacterial infections- Single-celled organisms are known as bacteria. These are also called prokaryotes. Researchers have found that there are almost 1 nonillion bacteria on earth. Bacteria have main shapes- spherical, rod-shaped and spiral. Examples of bacterial infections are- typhoid, cholera, tuberculosis, dysentery diphtheria etcetera. Bacteria can live in extreme environments from extreme heat to extreme cold, and even radioactive waste in any environment. Innumerable bacterial strains are present on Earth, some of which cause disease. Bad bacteria cause infection, and good bacteria kill bad bacteria and avoid disease. Some of the bacterial diseases that are infectious are cholera, tuberculosis, diphtheria, typhoid. These diseases are usually treated with the help of antibiotics. 

3. Fungal infections- A fungus breaks down (using an enzyme) and consumes organic material. Fungi grow and cause infections when good bacteria are destroyed. In the upper layers of the skin, many fungal infections appear, although some penetrate into the deeper layers. When inhaled, fungal spores can cause fungal infections involving the internal layers of the body. Fungus is a multicellular parasite that uses an enzyme to observe organic matter. Fungal infection generally develops on the upper layers of the skin. Examples of fungal infections are- Candidiasis, ringworm, histoplasmosis, athlete’s foot etc.

4. Prion disease- A prion has no genetic material and is a protein. In case the prion is abnormally folded, it impacts the brain system, which triggers dangerous diseases such as Creutzfeldt-Jakob Illness. Such diseases spread very quickly and are particularly deadly. They do not replicate in the host but stimulate anomalous behaviour in the cells of the body. A prion is basically a protein that causes no harm and contains no genetic material. Prions generally affect other parts of the nervous system. Diseases caused by Prion are rare, but in some cases, researchers have linked Alzheimer’s disease to Prion disease.

5. Other Infections- Also capable of causing communicable diseases are protozoa, helminths, and ectoparasites. Protozoa are transferred via faeces contact. Protozoan causes amoebic dysentery. Helminths encompassing flatworms and roundworms also cause human infections. Ectoparasites, including mites, lice, ticks, etc. stick themselves to the skin and induce infections.

Infectious Diseases Examples

Modes Of Transmission

Infectious diseases are transmitted through the following means, such as Air: Whenever an infected person sneezes or coughs, the droplets actually contain disease-causing pathogens. For example, chickenpox and measles may spread in the air and may infect others nearby. Bodily Fluids: Pass the pathogens to a safe individual by contacting an infectious individual or their bodily fluids such as spit, vomit, sweat, urine, etc.Surface Transmission: Touching an infected individual’s previously contacted objects or areas can cause the pathogen to transfer the infection to an unaffected person and cause illness.Sexual Transmission: Diseases like Syphilis and AIDS are sexually transmitted diseases

Measures to cure an infectious disease

Antibiotics are an effective medicine that can treat bacterial infections. Antibiotics generally cure urinary tract infections, renal infections, and strep throat. Antiviral medications are effective medications for treating infections like Hepatitis C, HIV, and influenza. Antifungal medications can be helpful in the treatment of valley fever, toenail infection, yeast infections, etc. Antiparasitic medications can cure infections like malaria and tapeworm.