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4. Through vectors: (example- malaria,

dengue)
Many animals which live with us may

carry diseases. Such animals or insects
that carry infectious diseases from sick

person to another potential host and
spread a disease are called vectors.

These animals act as intermediaries and

are the carriers of the disease causing pathogens.

Organ-specific and tissue-specific manifestation:
 Organ and tissue-specific manifestations refer to certain organs, tissues, or cells

where the microorganisms affect a person’s body.

 When the microbes affect the entire organ, such as lungs or kidneys, it is known
as organ-specific manifestation.

 When the entire tissue is affected by the microbes, it is called a tissue-specific

manifestation.
Organ-Specific Manifestation

● The microorganisms that enter the body travel to a specific organ and multiply

there. Mycobacterium tuberculosis is the bacteria that causes tuberculosis. It
usually enters the body through the nose and migrates to the lungs.

● Bacteria such as the Salmonella enter through the mouth (through consumption
of infected food or water) and travels to the gut lining causing typhoid.

● There are a few infectious agents that go to a particular organ and then spread
throughout the body. The HIV virus enters the body through sexual contact and

tends to spread to lymph nodes throughout the body.

● The malarial parasite enters the liver and spreads to the red blood cells. The
signs and symptoms of disease thus depend upon the tissue or organ it targets.

Tissue-Specific Manifestation
 The immune system is also activated in response to infections. The

microorganisms enter into the tissues and damage it.