2. INTRODUCTION
Saprophytes :are free-living microbes that live on dead or
decaying organic matter
Commensal: :normal bacterial flora of the body
Pathogen :can establish themselves and multiply in the hosts
1. Primary pathogen
2. Opportunistic pathogen
4. CLASSIFICATION
Infection occurs when germs enter your body and
multiply, resulting in disease. There are four main types of
infections:
Viral
Bacterial
Fungal
Parasitic
5. Viral infection
Viruses can cause a wide range of infectious diseases. Viruses cause illness by killing
cells or interfering with cell function.
The virus infiltrates a host's body and attaches itself to a cell, where it releases its
genetic material. The virus multiplies as the cell replicates. When a cell dies, more
viruses are released, infecting new cells. Some viruses alter the function of cells
rather than killing them.
Bodies frequently respond by inducing fever (heat inactivates many viruses),
secreting a chemical called interferon (which prevents viruses from reproducing) or
mobilizing the immune system's antibodies and other cells to target the invader.
6. 2. Bacterial infection
Bacteria cause a wide range of infectious diseases, including strep throat and urinary tract
infections, meningitis, and tuberculosis. Bacteria are also to blame for many skin rashes.
Bacteria can enter the body through wounds, scrapes, and surgical incisions, as well as the
mouth and nose. Some bacteria proliferate so quickly that they crowd out host tissues and
disrupt normal function. Some may kill cells and tissues right after they multiply.
Sometimes, these produce toxins that can paralyze, destroy cells or trigger a massive
immune response that is toxic.
Antibiotics are the first-line defense against bacterial infections.
7. 3. Fungal infection
Fungal infections are often more bothersome than dangerous. However, some can cause
serious illness.
Inhaling fungal spores is one of the most common ways for an internal fungal infection to
develop. Fungal spores are frequently found in decaying vegetation or on animal feces.
Fungal cells can invade the healthy tissues and disrupt their function. The body often
launches an immune response against fungal particles, which causes collateral damage to
the cells.
Infected people are treated with a combination of antibiotics and antifungal medications.
8. 4. Parasitic infection
Protozoa are a type of parasite that thrive on moisture and frequently spread disease via
water. Some protozoa cause intestinal infections, resulting in diarrhea, nausea, and
stomach upset.
In healthy people, parasites cause mild illness, but those with severely weakened immune
systems can develop serious infections that can spread to major organs.
Oral rehydration therapy is usually the first-line treatment. Antiparasitic drugs with a
broad spectrum of action can be used to treat severe cases
9. CLASSIFICATION
Primary infection: Initial infection
Reinfection: Subsequent infections by the same parasite
Secondary infection: new parasite infection in a host whose
resistance is lowered
Local infection: sepsis at localized sites such as appendix or
tonsils, generalized effects are produced.
Cross infection: When in a patient already suffering from a
disease a new infection is set up from another host
Nosocomial infections: Cross infections occurring in hospitals
are called nosocomial infections.
10. • Iatrogenic infection: physician induced infections resulting
from investigative, therapeutic or other procedures.
• Inapparent infection: clinical effects are not apparent.
• Atypical infection: the typical or characteristic clinical
manifestations of the particular infectious disease are not
present.
• Latent infection: Some parasites may remain in the tissues in a
latent or hidden form proliferating and producing clinical disease
when the host resistance is lowered.
14. INSECTS
• Blood-sucking insects such as mosquitoes, ticks, mites, flies, and
lice may transmit pathogens to human beings and diseases so
caused are called arthropod borne diseases.
• Insects that transmit infections are called vectors
Mechanical vector:
Biological vectors:
15.
16. MODES OF TRANSMISSION OF
INFECTION
Transmission is the process by which a
pathogen spreads from one host to another. Diseases or
infections are transmitted in many ways. It may be directly
transmitted from one person to another, or by certain bacteria,
viruses, protozoa, or fungi.
There are two different modes of transmission of diseases:
17. 1. Direct Transmission– This occurs when the pathogen is
transmitted directly from an infected person. For eg:- if an open
wound comes in contact with the blood of a Hepatitis B infected
patient, the wounded person might contract the disease.
2. Indirect Transmission- When the pathogens are not transmitted
directly from the infected person but through vectors such as flies,
mosquitoes, ticks, dogs, etc., it is known as indirect transmission.
18. Direct Transmission
1. Person to Person
When an infected person comes in contact with or exchanges body fluids
with a non-infected person. A mother can transmit infections to the unborn
child via the placenta.
2. Droplet Transmission
The droplets spread during sneezing, speaking, and coughing by an infected
person can spread infections. The infections can also spread by touching the
nose and mouth with the hands contaminated with infectious droplets. The
droplets are so minute that they travel only a short distance before falling.
The people nearby might contract infections.
19. 3. Spread by skin
There are a few infections such as chickenpox, conjunctivitis,
head lice, ringworm, etc., which spread when the skin of an
infected person comes in contact with the skin of the other person.
4. Spread through body fluids or blood
A few diseases spread when the body fluids or blood of an
infected person come in contact with the mucous membrane or
bloodstream of an uninfected person. Diseases such as hepatitis,
HIV, cytomegalovirus infections, etc. spread through semen and
vaginal fluids, saliva, breastmilk, urine, etc.
20. Indirect Transmission
1. Airborne Transmission
Some infectious agents remain suspended in the air for a long
period of time. These pathogens might attack the immune system of
a person in contact. E.g. if you enter a room that was initially
occupied by a patient of measles.
21. 2. Contaminated Objects
The objects around us carry pathogens. Touching the infected objects
which were initially used by a diseased person might render us diseased.
Contaminated blood and medical supplies can also spread infections.
3. Vector-Borne Diseases
Some infectious agents are transmitted by the blood-sucking insects. The
insects feed on hosts such as birds, animals, and humans and carry
infectious agents from them. These infections are transmitted to some
new host. Malaria and Lyme disease are the two vector-borne diseases.
22. 4.Food and Drinking Water
Improperly canned and undercooked food is the main source of
infections. Water also carries various pathogens from rivers and
lakes. It should be boiled or filtered before use. E.coli is transmitted
through contaminated food which causes various stomach
problems. Botulism is caused by the consumption of improperly
canned food. Cholera is one water-borne disease which has affected
millions of people consuming contaminated water.
23. 5.Transmission through Animals
When an infected animal bites or scratches against a person, it transfers the
infectious agents to the person. These agents can also be transmitted through
animal waste. When diseases are transferred from animals to people, zoonosis
occurs. Anthrax (sheep), rabies (dogs), plague (rodents) are some of the diseases
transmitted from animals to humans. Pregnant women and people with weak
immune systems are more prone to infections.
6.Environmental Factors
The infectious agents are present in soil, water and plants as well. These agents
can be transmitted to people and may cause diseases. For eg., Hookworm is
transmitted through contaminated soil.
24.
25. Different Modes of Transmission of Diseases
Disease Transmission Modes of Disease
Transmission
Diseases Caused
Direct Transmission Spread Through droplets Cold, cough
Spread by skin Conjunctivitis, chickenpox
Spread through blood or body
fluids HIV, Hepatitis
Person to person Gonorrhoea
Indirect Transmission Airborne transmission Measles, Influenza
Contaminated objects Cold, syphilis
Vector-borne transmission Malaria, Lyme disease
Transmission through food and
water Cholera, diarrhoea
Transmission through animals Rabies, anthrax
