Disease:

A disease is a condition that affects the normal functioning of an organism, causing harm or discomfort. It can be caused by genetics, environment, lifestyle, or infection. A disease has a more objective, biological, or pathological basis. While often used interchangeably, “disease” and “illness” have distinct meanings. An illness is a person's subjective experience of feeling unwell. It may or may not be related to a specific disease. While disease focuses on the medical aspect, illness includes personal, social, and cultural factors.

Types of diseases according to duration:

According to duration, diseases are of two types:

1. Acute Diseases: Short-term diseases that resolve on their own or with treatment (e.g., pneumonia).
2. Chronic Diseases: Long-term diseases that persist or worsen overtime (e.g., diabetes).

According to causes, diseases are either infectious or non-infectious.

Infectious disease:

Infectious diseases can spread from person to person or from animals to people. An infection occurs when a pathogen enters and multiplies inside a person's body, causing disease. A pathogen is an agent that causes disease or infection. Types of pathogens include viruses, bacteria, fungi, protozoans and parasitic worms.

They can spread in several different ways, through: skin contact, the transfer of bodily fluids, with faeces, ingesting contaminated food or water, inhaling airborne particles or droplets, touching an object that a person carrying the pathogen has also touched.

Types of Infectious Diseases:

The types of infections are viral infection, bacterial infection, fungal infection, protozoan infection and parasitic infection.

Types of pathogens, their description, examples and diseases:

Zoonotic disease:

A zoonotic disease or zoonosis is an infectious disease that is directly transmitted from animal to humans, such as rabies and bird flu. Almost any animal can carry zoonotic disease e.g., mammals, birds etc.

Causes zoonotic diseases:

Many different pathogens can cause zoonosis. These are viruses, bacteria, Parasites (protozoa and parasitic worms), fungi.

Symptoms of zoonotic diseases:

Symptoms of zoonotic diseases vary depending on the specific illness. For example, symptoms of bird flu are fever, cough, tiredness, muscle aches, sore throat, shortness of breath, runny nose and headache.

Types of Zoonotic Diseases:

1. Viral zoonoses: The examples of diseases caused by zoonotic viruses are rabies which can be transmitted from all mammals and bird flu which is transmitted from birds.
2. Bacterial zoonoses: Examples of bacterial zoonoses are anthrax which is transmitted from cattle and plague which is transmitted from rat fleas.
3. Fungal zoonoses: The example of zoonoses caused by fungus is ring worm which is transmitted from cats and cattle.
4. Protozoan zoonoses: Examples of protozoan zoonoses are African sleeping sickness which is transmitted from an African fly and beaver fever which is transmitted from beavers.
5. Parasitic worm zoonoses: Examples of parasitic worm zoonoses are snail fever which is transmitted from snails and tape worm which is transmitted from pig.

Transmission of Zoonotic Diseases:

Zoonotic illness can spread through bites, scratches, inhalation, ingestion, or contact with contaminated animal waste or products.

Vector Borne Diseases:

A vector is a living organism that transmits an infectious agent from an infected animal to a human or another animal. Vectors are common insects that carry and transmit diseases causing bacteria, viruses and parasite. The examples of vector are mosquitoes, ticks, flies, fleas and lice etc. Vectors may be biological vectors are mechanical vectors.

1. Biting vectors: The examples are mosquito, mite, flea and tick. They may carry pathogens that can multiply within their bodies and be delivered to new hosts, usually by biting.
2. Carrier vectors: The example is flies that can pick up infectious agents on the outside of their bodies. Then they and transmit infectious agents through physical contact. Examples of vector-borne diseases include Dengue fever, Lyme disease, and malaria etc.

Vector-Borne Diseases:

Vector-Borne Diseases are transmitted through vectors like insects. For example, malaria and dengue are spread by mosquitoes. A vector is an organism that acts as an intermediate host for a pathogen. Most importantly the vector transfers the pathogen from one host to the next host.

Non-infectious diseases are not caused by pathogens and cannot spread from person to person. These include:

1. Physiological diseases (e.g., type 2 diabetes, cancer)
2. Genetic disorders (e.g., sickle cell anaemia, colour blindness)
3. Autoimmune diseases (e.g., type 1 diabetes, rheumatoid arthritis)
4. Nutritional deficiency diseases (e.g., scurvy, rickets)
5. Environmental diseases (e.g., lung cancer from smoking, skin cancer from UV rays)
6. Degenerative diseases (e.g., osteoarthritis, Alzheimer’s disease)
7. Psychological disorders (e.g., anxiety disorders, depression)

Covid 19:

You all are familiar with Covid–19. It was a global pandemic during 2020–2022. COVID–19 is caused by the coronavirus SARS–CoV–2. It is an acute disease.

It affects the body in many ways:

1. Respiratory System:
   Causes breathing difficulties and pneumonia.
2. Cardiovascular System:
   Increases the risk of heart attacks and strokes.
3. Nervous System:
   Leads to headaches, fatigue, and loss of taste and smell.
4. Digestive System:
   Causes diarrhoea, nausea, vomiting and liver damage.
5. Urinary system:
   Leads to abnormal kidney function and kidney damage.
6. Immune System:
   Weakens the immune response.
7. Mental Health:
   Leads to anxiety, depression, and stress.
8. Long-term Effects:
   May cause lasting lung damage and other health problems.

Prevention:

COVID–19 can be prevented by following practices:

1. Washing hands frequently
2. Wearing masks
3. Social distancing
4. Staying home if symptomatic
5. Vaccination

HIV (Human Immunodeficiency Virus) attacks the immune system, specifically helper T cells (CD4 T cells). It weakens the body’s ability to fight infections. Without treatment, HIV can lead to AIDS (Acquired Immune Deficiency Syndrome) which is a chronic disease. The symptoms of AIDS include fever, headache, muscle aches, joint pain, swollen lymph nodes, diarrhoea, weight loss and severe immune dysfunction. In the final stages due to immune dysfunction lots of opportunistic infections attack the patient.

HIV is transmitted through patient’s blood and body fluids. Infected needles, blood and instruments are mainly responsible for the spread of this disease. After infection there are four clinical stages showing the progression from HIV to AIDS. Stage 1 is without any symptoms and it lasts for few weeks. Stage 2 has mild symptoms and it can last up to 10 years. In stage 3 the immune system weakens and opportunistic infections start to appear.

Diabetes:

Diabetes is a group of metabolic disorders characterized by high blood sugar levels. It is a chronic disease.

Its main types include:

1. Type 1 Diabetes (T1D): It is a chronic disease. An autoimmune disease destroying insulin-producing cells in the pancreas. It can be treated by taking regular injections of insulin.
2. Type 2 Diabetes (T2D): It is a chronic disease. A metabolic disorder from insulin resistance and impaired insulin secretion.
3. Gestational Diabetes (GDM): Develops during pregnancy. Most cases of gestational diabetes will resolve shortly after delivery. Proper management includes medication, diet, and lifestyle changes.

Effects of unmanaged diabetes include:

1. Short-term effects: Increased thirst, urination, fatigue, blurred vision, slow-healing wounds.
2. Long-term effects: Heart diseases, high blood pressure, irregular heartbeat, kidney damage, nerve damage, retina damage, high cholesterol level, high lipid level, high uric acid level, high risk of COVID-19, ketoacidosis, foot ulcers and memory loss.

• Be more active.
• Eat fiber rich foods.
• Eat whole grains.
• Lose weight.
• Make healthier choices.
• Don't smoke.

Plant diseases in Pakistan:

Pakistan is an agricultural country. Crops and their yields are the back bone of our economy. Some, common plant diseases caused by fungi in Pakistan are following.

1. Rust: Wheat leaf rust is a fungal disease caused by Puccinia rust fungus, it infects plants such as wheat, barley, rye. It gets transmitted from one plant to another through spores or air. Rust infections can lead up to 20% yield loss.
2. Smut: Smut is also a fungus that affects wheat crops and some grasses. Smut gets its name from the sooty, black appearance of infected wheat plants. The fungus produces spores in the leaves, grains or ears. These fungi are damaging pathogens of cereal crops, reducing yield and quality of harvested grain. It is caused by fungi Ustilago tritici.
3. Red rot of Sugarcane: Red rot is a very serious disease of sugarcane. The main symptom of the disease is the reddening of the internal tissues and reduced sugar content. It is caused by fungi Colletotrichum falcatum.

Effective disease management includes resistant varieties, crop rotation, and fungicides, along with proper diagnosis and monitoring.

Antibiotics:

Antibiotics are chemicals produced by microorganisms which are capable of destroying or inhibiting the growth of another microorganism. The microorganisms that produce antibiotics are mostly bacteria and a few fungi. Now synthetic antibiotics are also available. Antibiotics are effective against bacterial infections but are of no use against viruses.

Discovery of Penicillin:

The discovery of penicillin is attributed to Alexander Fleming in 1928. He was studying bacteria in his lab. He left a dish with bacteria uncovered. When he returned to his laboratory after a holiday, he noticed a mold, Penicillium notatum, growing on that bacterial culture. To his surprise, the mold killed the bacteria around it. He realized the mold was producing a special substance that could kill a wide range of harmful bacteria. He isolated the substance and named it penicillin. Fleming thought penicillin could be used to treat bacterial infections, but he needed help to develop it. He worked with two other scientists, Florey and Chain, to purify and mass-produce penicillin.

Finally, penicillin was ready to use, and it revolutionized the treatment of bacterial infections. It saved many lives and became a widely used medicine. In short, Fleming’s discovery of penicillin was an accident that led to a breakthrough in medicine, it has been estimated that Penicillin has saved over 500 million lives.

Penicillin was the first successful antibiotic used in medicine. From 1940s to 1960s it was widely used throughout the world against bacterial infections. But afterwards many bacteria get resistant against penicillin. Penicillin is still used to treat some bacterial infections.

Mode of Action of Antibiotics:

Antibiotics work by targeting specific biochemical processes in bacteria, ultimately leading to their death or inhibition of growth by inhibiting cell wall synthesis, protein synthesis, DNA, replication and metabolism.

1. Cell Wall Inhibition: Antibiotics like penicillins and cephalosporins inhibit the synthesis of the bacterial cell wall, causing it to weaken and eventually burst.
2. Protein Synthesis Inhibition: Antibiotics like tetracyclines and erythromycin bind to the bacterial ribosome, preventing protein synthesis and essential cellular functions.
3. DNA Replication Inhibition: Antibiotics like gentamicin bind to the bacterial DNA, inhibiting replication and repair.
4. Membrane Disruption: Antibiotics like polymyxins interact with the bacterial cell membrane, disrupting its structure and function.
5. Metabolic Inhibition: Antibiotics like sulfonamides inhibit specific metabolic pathways, depriving bacteria of essential nutrients.

By targeting these critical processes, antibiotics effectively prevent bacterial growth and proliferation, helping to clear infections.

Classification of Antibiotics: Evaluation and Overview

Antibiotics can be classified in several ways based on structure, mechanism of action, spectrum of activity, and source. This classification helps in selecting the right antibiotic for treatment and understanding its potential side effects or resistance risks.

1. Based on Mechanism of Action:

   Class	How It Works	Example
   Cell wall synthesis inhibitors	Prevent bacterial cell wall formation	Penicillin, Cephalosporins
   Protein synthesis	Disrupt bacterial protein production	Tetracyclines, Macrolides

Based on Spectrum of Activity:

Based on Source:

Antibiotics are essential in medicine, but their overuse and misuse have contributed to antibiotic resistance. Antibiotic resistance in bacteria refers to the ability of bacteria to survive and grow in the presence of antibiotics, which are designed to kill or inhibit their growth. This occurs when bacteria develop mechanisms to avoid the effects of antibiotics, making these life-saving drugs less effective. It leads to untreatable infections that result in increased mortality, require longer treatment, increasing healthcare costs and make certain medical procedures risky. For example, drug resistant typhoid, drug resistant TB etc. The development of resistance in bacteria is a natural process that occurs through various mechanisms of resistance.

Mechanisms of resistance:

Antibiotic resistant bacteria utilize following mechanisms:

1. Enzyme production: Bacteria produce enzymes that degrade antibiotics.
2. Alter target site: Bacteria modify their target sites, making antibiotics less effective.
3. Active efflux: Bacteria pump antibiotics out of their cells.
4. Biofilm formation: Bacteria form protective biofilms, reducing antibiotic effectiveness.

Factors Contributing to resistance:

There are many factors which are responsible for increasing antibiotics resistance in pathogenic bacteria. These include excessive use of antibiotics for humans, agricultural use in animal feed and lack of new antibiotic development.

Prevention:

To combat resistance, it’s essential to:

1. Use antibiotics judiciously:
   Only use antibiotics when necessary.
2. Develop new antibiotics:
   Invest in research and development.
3. Improve infection control:
   Enhance sterilization and hygiene practices.
4. Monitor and track resistance:
   Surveillance and data collection to inform strategies.