PATHOLOGY

1. FISH AND SHELLFISH DISEASES

2. Introduction
Pathology
Pathology is defined as study of disease and their
causative agents.
Disease
Disease is due to the change in existing environment
i.e. something change from the normal metabolism
or activity of the animal.
Incidence of disease is due to the breakdown of the
delicate balance between host, pathogen and
environment (Snieszko, 1970)

3. Pathogen Types
Obligate pathogen
• Organism which will cause disease because of the mere
presence in the culture system
• This is mainly due to the interaction between animal and
environment.
Aeromonas salmoniclda
Opportunistic pathogen
• Organisms which will not cause diseases even if it is
present in the culture system until other stressors limit
the capacity of animal.
Eg. Vibrio sp in shrimps

4. Stress
Is the sum of all the physiological responses by which
an animal tries to maintain or re-establish a normal
metabolism in the face of a physical or chemical
force (Selye ,1950) .

5. General Adaptation Syndrome (GAS)
• The changes which occur in response to
environmental stress
• animal ties to adopt its original condition is said to
be General adaptation Syndrome (GAS).
Steps involved in GAS
• Alarm reaction
• Stage of resistance
• Stage of exhaustion

6. Alarm reaction
• This is due to physical change i.e. animal escapement
due to external stimuli, physiology. If oxygen is lost in
bottom layers of water column animal comes to top.
• chemical change i.e. change in pH or dissolved oxygen
or amount of ammonia . Animal cannot escape.
Stage of resistance
• In response to Physical, Biochemical or microbiological
strssors animal will produce counter effect to maintain
the normal condition to achieve homeostasis.
• This stage helps to know whether the animal gets the
disease or not.

7. Contd…..
Stage of exhaustion
• When the animal is unable to achieve homeostasis
i.e. resistance / change. The animal gets exhausted. If
it reaches this stage leads to disease.
• When an animal course these three stages and
comes back to the normal condition, the animal does
not have disease.
• If the animal does not come back to the normal
condition prone to disease.

8. Characteristics of GAS
• The changes occurring during the GAS are neither
species specific nor stressor specific: anoxia,
infection, fright, forced exercise, anesthesia and
many other stressors provoke similar responses in
higher and lower vertebrates.
• Totality of response to each individual stressor will
vary, and be composed of some reactions specific to
that particular stressor, and others which are
common changes of the GAS regardless of the nature
of stress.

9. Adaptation of animals in GAS
• The hypothalamus senses the stress by HPI axis –
Hypothalamic pituitary Interrenal axis.
environmental stimuli carried by means of sensory
neuron to the hypothalamus which in turn activates
pituitary.
• Further adaptations to adverse conditions is
mediated by secretion of hormones such as Cortisol,
ACTH (Adrenocorlicotiophic hormone) by pituitary
and Thyroxine by downstream activation of thyroid
gland.

10. Factor or parameter causing stress
Temperature
• As fishes are cold blooded animal (Poikilothermic) it
can change the body temperature depending upon
surrounding and this has profound influence on
animal health status.
• As the animal approaches the temperature extremes
for its survival chances for pathogen invasion
increase.
• Sudden temperature change rather than
temperature per se thatis the stressor.

11. Inflammation In: Higher vertebrates
• Inflammation – It is a change happening in animal
due to a stressor. The cardinal signs of inflammation
in the higher vertebrates are
• Calor (heat) - This is due to increased physical activity
• Rubor (Redness) - This is due to the dilation of
capillaries due to the increase in the blood flow into
the area of infection.
• Tumor (swelling) –increased dimaeter of capillary
fenestrae allow the largest serum protein molecules
such as fibrinogen and immunoglobulin to exude into
the tisssue.

12. Contd….
• Doloro (pain) -The nerve encircling the area of
assault will be stretched which carry message and
cause pain.
• Et functio laeso (Loss of function)- It happens when
the integrity of the system is damaged or broken.

13. Inflammation in vertebrates
• As fishes are cold blooded animal except capacity to regulate
body temperarture all the factors are found in vertebrates.
• In vertebrates inflammatory response happens through
multiple chemical changes at tissue level.
• The Pharmaco dynamic amine (histamine and 5-
hydroxytryptamine) is a chemical compound produced from
mast cells.
• These amines will have a cascading effect.
• It also produces Vasoactive amine (related to blood
capillaries) that starts dilation.
• The cells like lymphocytes and Thrombocytes (Platelets) are
accumulated at the site of Inflammation.

14. contd…
The cells which leave the blood include.
• Neutrophils (Polymorphonuctear leucocytes)
• Monocytes (Mononuctecu macrophages)
• Lymphocytes
• Thrombocytes

15. Types of Inflammation
• Acute Inflammation
• Chronic Inflammation
Acute inflammation
• These happen for short duration. There are three
response normally happening during the process.
– Resolution
– Exudates / Exudation
– Necrosis

16. Contd…
Resolution
The cause of inflammation is countered rapidly
return to normal.
Exudates/ Exudation
continuous production of the products of the
inflammatory response.
Based on the site and stimulus may be suppurative,
catarrhal, fibrinous, serous or diptheretic.

17. Necrosis
• Necrosis is the death of the cell.
• Resolution and Exudation is reversible.
• But necrosis is not reversible.
• This is caused due to prolonged inflammation. At
this stage the inflammatory response ends.

18. Types of necrosis
Liquefactive necrosis
It is due to the release of enzymes at particular site
resulting in enzymatic digestion of cells.
Mediated by either the host cell itself such as
neutropils or lysosme or by lytic toxins produced by
infecting bacteria.

19. Contd…
Coagulative Necrosis
• When the group of blood vessels supplying blood
to tissue is cut off the cell will due to the loss of
blood supply (ischaemia) to an area.
• In sections recognised as an acidophilic are where
cell nuclei are destroyed but outlines still visible.
• When the coagulative necrosis area invaded by
saprophytic bacteria capable of digesting the dead
tissue, the necrosis is said to be gangrenous.

20. Contd…
Fat necrosis
The area having fat is digested by enzymes produced
by pathogens.
Lipase are produced and fat is digested which lead to
the formation of soap like material.

21. Sages of necrosis
Best characterised in terms of changes taking place in
nucleus of cell.
3 stages have been identified
1. Pyknosis 2. Karyohexis 3. Karyolysis
Pyknosis
Here the nucleus is shrunken and become very dark.
Karyohexis
characterized by rupture of the nuclear membrane
and fragmentation of the nuclear chromatin.

22. Contd…
Karyolysis
• As the nucleic acid are hydrolyzed, they lose their
basophilia and the whole tissue assumes a shiny
pink colour.
• Due to persistence nature of strands of fish
chromatin nucleus appear as very dark,
haematoxylinophilic irregular tadpole or
trypanosome shaped structure usually against a pale
shiny structureless back ground.

23. Chronic Inflammation
Chronic inflammation:- In case acute inflammation is
not resolving quickly, then Chronic inflammation
results characterized by contemporaneous
inflammation and proliferation of neighbouring
support tissues.
Granuloma formation:- Chronic inflammation many a
times lead to a condition called as granuloma. It is a
white to yellow lesion which may have a cheesy or
hard consisitency or even may be calcified.
May be caused by silicaceous diatoms, bacteria or
fungi.

24. Thanking you