General Veterinary Pathology

DEFINITIONS

• Pathology literally means study of disease or discourse of disease
• Pathology is that branch of medicine treating of the essential nature of disease especially of the changes in body tissues and organs which cause or caused by disease (Dorland).
• Pathology is study of the molecular, biochemical, functional and morphological aspects of diseases in the fluids, cells, tissues and organs of the body. Summary: Pathology is study of the functional and morphological alterations in tissues and fluids of the body during the disease (Thomson, 1984)

Health

• Normal condition of the body and mind i.e. with all the parts functioning normally.

Disease (Dis – Negative ease)

• Any deviation from or interruption of normal structure or function of any body part, organ, or system that is manifested by a characteristic set of symptoms and signs whose aetiology, pathology, and prognosis may be known or unknown.
• Disease is any departure from healthy state.
• The following are the essential components in the study of diseases :

Aetiology

• The science dealing with causes of disease
• Study of causation of disease

Incubation period

• Incubation period is the time that lapses between the action of a cause and manifestation of disease.

Pathogenesis

• Pathogenesis is development of morbid conditions or of disease or mechanism by which the causes produce diseases. e.g. In traumatic reticuloperitonitis in cattle sharp objects like nails ingested are usually trapped in the reticulum.
• Movement of reticulum and pressure from pregnant uterus in cows favours the piercing of foreign body through the wall of the reticulum, setting up reticulitis and then into peritoneal cavity causing injury causing peritonitis.
• If the foreign body is carrying pyogenic organisms purulent inflammation is found.

Clinical signs

• Clinical signs are outward manifestations of the patient’s suffering from diseases while alive.

Lesions

• Lesions are macroscopical (visible to naked eye) or microscopical changes in tissue structure.

Pathognomonic lesion(s)

• Pathognomonic lesion(s) is/are characteristic for a particular disease e.g. Blue tongue in sheep- Haemorrhages in the base of the pulmonary artery and base of the aorta.

Course of the disease

• Course of the disease is the duration of time through which the series of changes characteristic of disease pass through to their ultimate end.

Termination of disease

• Termination of disease is recovery or death or may prolong for a considerable length of time as in chronic disease.

Diagnosis

• Diagnosis is the art of determination of the nature of disease, its causes, symptoms, lesions etc.

Morphological diagnosis

• Where diagnosis is based on the alterations observed in a tissue or organ. i.e. naming the lesion e.g. Pneumonia (Inflammation of lungs), enteritis (Inflammation of intestine). This provides information to clinician on the extent, duration, distribution and type of lesion.

Aetiological diagnosis

• Where specific cause of the disease can be identified i.e. naming the cause. e.g. Cause of pneumonia-Bacteria, virus, fungus, foreign body

Specific or definitive diagnosis

• Where the pathognomonic lesions are characteristic of the disease can be observed. i.e. naming the specific entity involved e.g. Corrugated appearance of intestine in Johne’s disease in cattle, haemorrhages in the base of the aorta and pulmonary artery in blue tongue in sheep

Differential diagnosis

• Differential diagnosis is aimed at diagnosing a disease by differentiating from different diseases based on clinical and pathological findings. This is the first step in diagnosis.

Prognosis

• Prognosis is pronouncing probable/expected outcome of the disease
• Prognosis of a disease is the estimate by a clinician of probable severity and outcome of the disease.

Sequelae

• Final end result of the disease

Morbidity

• Morbidity is the percentage of affected animals that get exposed
• Number of animals exposed is 100
• Number of animals affected is 50
• Morbidity 50%

Mortality rate

• Mortality rate of a disease is the percentage of deaths among animals affected by that disease.
• Number of animals exposed is 100
• Number of animals affected is 60
• Morbidity 60%
• Number of deaths among affected animals 30
• Mortality rate 50%

Autopsy

• Autopsy is seeing with one’s own eyes (Used in human medicine)
• The pathologist cuts open a corpse to see the lesions in diseases.

Necropsy

• Necropsy is seeing a carcass (Used in veterinary medicine)

Biopsy

• Biopsy is examination of biological samples like fluid, tissue, etc., collected from living animals.

Scope of Pathology

• Pathology is aiding in the diagnosis of diseases.
• Helps in understanding the disease process.
• Hence, prognosis, control and rationale treatment and prevention are possible.