Communicable Diseases

This section explains communicable diseases, covering how pathogens spread, how pathogens cause harm, how the spread of disease is prevented and the lysogenic and lytic life cycle of viruses. Communicable diseases are diseases that can be transmitted from one individual to another. These diseases are caused by pathogens, which are microorganisms like bacteria, viruses, fungi, and protists. Communicable diseases can spread directly from person to person or indirectly via vectors (such as insects) or contaminated surfaces. These diseases can affect anyone, regardless of age or health, and they are a major cause of illness and death worldwide.

Some common communicable diseases include:

• Influenza (Flu) – caused by a virus
• Tuberculosis (TB) – caused by bacteria
• Malaria – caused by protists
• Athlete’s foot – caused by fungi

How Pathogens Spread

Pathogens can spread in a variety of ways:

• Direct contact: This includes physical contact, such as shaking hands or sexual contact.
• Airborne transmission: Pathogens can be inhaled through the air, often when an infected person coughs or sneezes.
• Waterborne transmission: Pathogens can spread through contaminated water (e.g., cholera).
• Vector transmission: Vectors, such as mosquitoes or ticks, can carry pathogens from one host to another.
• Contaminated surfaces: Pathogens can spread through surfaces that have been touched by infected individuals.

How Pathogens Cause Harm

Once inside the body, pathogens can cause harm in several ways:

• Bacteria: Bacteria can produce toxins that damage tissues, leading to symptoms like fever, inflammation, and pain.
• Viruses: Viruses invade host cells, taking over the cell’s machinery to reproduce. This causes the host cell to burst, leading to tissue damage and symptoms like fatigue and swelling.
• Fungi: Fungi can cause infections on the skin or in internal organs. They feed off the host, damaging tissues and leading to symptoms like rashes or sores.
• Protists: Protists are single-celled organisms that can invade tissues and damage cells, often causing conditions like malaria, where red blood cells are destroyed.

How the Spread of Disease is Prevented

There are various ways to prevent the spread of communicable diseases:

• Good hygiene: Washing hands regularly with soap and water, using tissues when coughing or sneezing, and cleaning surfaces reduce pathogen transmission.
• Vaccination: Vaccines help the body’s immune system recognise and fight off specific pathogens before infection occurs.
• Antibiotics and Antivirals: These medications are used to treat bacterial and viral infections, respectively. Antibiotics must only be used for bacterial infections to prevent antibiotic resistance.
• Quarantine and isolation: Infected individuals should be isolated to prevent the spread of contagious diseases.
• Insect control: Using insect repellent, nets, and eliminating breeding grounds for vectors like mosquitoes can prevent diseases like malaria.
• Safe drinking water: Ensuring access to clean water and proper sanitation reduces the risk of waterborne diseases.

Table of Bacterial Diseases

Table of Fungal Diseases

Table of Viral and Protist Diseases

The Influenza Viral Life cycle

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Lysogenic and Lytic Life Cycle of Viruses

Lytic Cycle:

In the lytic cycle, the virus infects a host cell, uses the cell’s machinery to replicate itself, and causes the cell to burst (lyse), releasing new virus particles. This process leads to the immediate destruction of the host cell and the spread of the virus.

Steps:

1. Virus attaches to the host cell and injects its genetic material.
2. The viral DNA/RNA takes over the host cell's machinery to replicate and transcribe its own genetic material.
3. New viral particles are assembled.
4. The host cell bursts, releasing the new viruses to infect other cells.

Lysogenic Cycle:

In the lysogenic cycle, the viral DNA integrates into the host cell’s DNA and becomes dormant. The viral genes are replicated along with the host cell’s genetic material, meaning the virus can lie dormant for a long time before becoming active.

Steps:

1. Virus attaches to the host cell and injects its genetic material.
2. The viral DNA integrates into the host cell’s DNA, becoming a prophage.
3. As the host cell divides, the viral DNA is replicated along with the host DNA.
4. Under certain conditions, the viral DNA may become active, entering the lytic cycle and causing the production of new virus particles.

Summary

Communicable diseases are caused by pathogens like bacteria, viruses, fungi, and protists. They can be spread in various ways, including through direct contact, air, water, and vectors. Prevention methods such as good hygiene, vaccination, and proper medical treatments can help control the spread of these diseases. Understanding the life cycles of viruses and the different ways pathogens cause harm is important in the fight against infectious diseases.