Animal Health Lecture 2

Define disease

deviations from normal health or physical, or mental being

• any disordered or incorrectly functioning organ, part, structure or system of the body

• Diseases can occur due to external factors or internal factors

Do we need an infection for a disease to happen?

No, diseases can occur without infections. Internal imbalances or genetic factors also contribute to disease.

• mental disease

• cancer

• diabetes

Non- Infectious diseases

Do not arise from pathogens and are caused by transmissible agents

• can be due to environmental factors

• can cause symptoms and may result in serious health conditions to the animal

Envoirmental factors

• trauma (broken arm or being wounded)

• Non-Infectious agents (posion)

• Nutritional deficiencies (Rickets due to vitamin D deficiency)

• Dehydration, heat stroke, frost bite

Internal factors

• neoplasia (cancer)

• congenital defects (cleft lip)

• Genetic/Metabolic disorders (Diabetes type 2, or hip plsma in certain dog breeds)

• Allergy, heart or renal failure, etc.

Infectious disease

when a body is disturbed by a foreign invader capable of replcating and disturbing homeostastis often causing symtoms

• can either be contagious or non-congious

Contagious

Disease can spread from one animal to another directly (Flu, salonellosis, tuberculosis)

Non-contagious

Diseases do not spread directly between animals and require special conditions (Tetanus, Gas gangrene)

Do all infections cause disease

No

• A microorganism ability to cause a disease depends on 2 things, its virulence and the hosts resistance

Virulence

The severity and harmfulness of a microorganisms ability to cause disease

• microorganisms with higher virulence have greater potential to cause severe illness

5 factors affecting virulence include

1. The ability to produce toxins and enzymes

2. the ways it can invade and evade the host

3. the ability to mutate

4. replication rate

5. transmission mechanisms

resistance vs disease challenge

An animal will reamin healthy as long as the animals resistance is greater than the disease challenge. However if the resistance is reduced for any reason or the disease challenge becomes stronger, the disease will appen

How many lines of defense

two

1st line of defense

1. Physical barriers

2. Chemical barriers

3. Microbiome

2nd line of defense

Inante and adaptive immune system

Physical barriers

1. Skin

2. Epithelial tissues (G.Im respiratory, Urinary/reproductive)

Chemical barriers

1. Salivia

2. Mucus

3. Tears

4. Stomach acid

Saliva

Contains enzymes capable of attacking some agents of siease

Mucus

A slimy protein containing fluid lining most internal epithelial layers Traps particulates and microbes for elimination

Tears

Contain enzymes capable of attacking some agents of disease

Stomach acid

Low pH kills microbes and may deactivate some other agents

Good bacteria

Good bacteria compete with harmful ones. These bacteria live in sunuses, mouth and along the GI track

Innate immunte system

Composed of phagocytes like neutrophils and macrophages

• reacts the same way every time it encounters an agent

• if defeated once may fail against subsequent exposures

• offers immediate but relatively generalized defense

Adaptive immune system

Composed of T cells and B cells

• learns from the first encounter with an agent

• reacts more strngly and effectively upon subsequent exposures

T cell role

Can directly kill or assist B cell response

B cell role

produce antibodies targeting specific antigens

Antibody role

neutralize targets and mark them for destruction