Role of white blood cells in the diagnosis of diseases in animals
Dr. Jayant Bhardwaj, Dr. Yamini Verma, Dr. Madhu Swamy , Dr. Amita Dubey
Department of Veterinary Pathology , College of Veterinary Science & Animal Husbandry , Jabalpur ( M.P. )
White blood cells ( WBCs ) are considered as the complete cells which have a nucleus and organelles. Since they lack haemoglobin, therefore they are colourless and are also called as leucocytes which is a Greek word meaning ‘leukos’ as ‘white’ and ‘cyte’ as ‘cell’ . They are mainly responsible for body’s defense mechanism against pathogens and thus play a major role in the diagnosis of diseases in animals .Whenever any pathogen enters the body, then the marked changes are observed in their number .
Types of white blood cells – White blood cells are categorized into 2 on the basis of presence or absence of granules.
- Agranulocytes – They lack visible cytoplasmic granules . These include lymphocytes and monocytes .
- Granulocytes – They have visible cytoplasmic granules . These include neutrophils , basophils and eosinophils .
Leucopoiesis – It is the formation of white blood cells ( WBCs ) . The granulocytes originate from the bone marrow. The multipotent stem cell develops into unipotent haemopoetic line which in course of division forms neutrophil, eosinophil and basophil. The successive stages of division of myeloblast are progranulocyte, myelocyte, metamyelocyte, band cells and ultimately mature granulocytes.
Monocytes originate in spleen and bone marrow from the monoblast with intermediate stage as promonocyte .
Lymphocytes formed in lymph tissues , lymph nodes , Peyer’s patches , spleen , tonsil and thymus from lymphoblast with intermediate stage as prolymphocyte .
Neutrophil – Neutrophils are the first line of defense against microbial infection and are important participants in inflammatory reactions . Nucleus of a neutrophil is generally divided into lobes connected by filaments . It’s cytoplasm has granules which stain with neutral dyes .In aves , it is called as heterophil .
Eosinophil – It’s nucleus is less lobulated and usually contains 2 lobes . The cytoplasm granules stain with acid dyes .
Basophil – They are very less in number in the circulation .It’s nucleus is elongated or bend in S form .Usually it’s cytoplasm stain with basic dyes .
Monocyte – It is the largest cell of the blood with size 12 -22 micrometre in diameter with oval or horse shoe shaped nucleus .
Lymphocyte – It’s nucleus is large and round and is placed a little eccentric with a thin rim of cytoplasm
Role in diagnosis of diseases –
Absolute and relative leucocyte counts – In case of differential leucocyte count performed manually , minimum of two hundred cells should be identified but in leukopenia count as many cells as possible . The chances of errors are less with absolute values as compared to the percentages .
Various physiologic or pathologic causes results in variations in leucocyte numbers . Suffix “ – osis “ or “ philia “ is used to denote an increase in the number of various leucocytes above the normal value ; while the suffix “ – penia “ is used to denote a decrease in the number of various leucocytes below the normal value . The nature of the various disease processes and the body’s response to them can be indicated by the quantitative and qualitative changes in a particular leucocyte type .
Leucocytosis — It can be defined as an increase in the number of circulating leucocytes above the normal range.
Physiologic leucocytosis – It is usually seen in muscular exercise , excitement , emotional disturbance etc.
Pathologic leucocytosis – It is observed in infections like pyometra , metabolic intoxications like uremia, acidosis, eclampsia , foreign protein reaction , insect venom, tissue necrosis , acute haemorrhage, acute hemolysis, neoplasia like leukaemia , adrenal corticosteroid etc.
Leucopenia – It can be defined as a decrease in number of circulating leucocytes below the normal range. It is observed in viral infections like feline panleukopenia , Canine distemper , infectious canine hepatitis , lymphosarcoma in cats , feline infectious peritonitis , picornavirus infection , hogcholera , swine influenza , blue tongue, malignant catarrhal fever , bovine viral diarrhoea , rinder pest, psittacosis – granuloma infection of cattle , viral arteritis in horses , bacterial infection, rickettsial infection like ehrlichiosis in dogs and horses, protozoal infections like toxoplasmosis, East coast fever . It can also be seen due to sequestration of leucocytes in capillaries of lung , liver and spleen due to endotoxic , septic or anaphylactic shock and due to their retention in normal reservoirs ; bone marrow hypoplasia , bone marrow dysplasia ; deficiency of vitamin B12 and folic acid . It can also be found when drugs like chloramphenicol , streptomycin, penicillin , griseofulvin , aspirin, phenacetin, phenylbutazone , antipyrine , pyribenzamine, primidone, dilantin, thiouracil , propylthiouracil, cytoxan, 6- mercaptopurine , arsphenamine, mapharsen, DDT , barbiturates , pyrimethamine , chlorpromazine , metallic poisons like lead, thallium , mercury , arsenic etc. are either given or ingested by animals .
Neutrophilia – It can be defined as an increase in the total number of neutrophils in the blood above the normal range. It can be observed in endogenous release of corticosteroids, trauma , neoplasm, surgical procedures , anaesthetics , some metabolic and endocrine disorders, intoxication , hyperadrenocorticism , stress, inflammation etc.
Neutropenia – It can be defined as the decrease in the total number of neutrophils in the blood below the normal range. Deficiency of functional neutrophils in the peripheral blood , overwhelming bacterial infection , viral infections , rickettsial infection , hypersplenism , sequestration of neutrophils in capillary beds in conditions like shock , initial stage of acute bacterial infection, reduction of granulopoiesis in bone marrow , deficiency of vitamin B12 and folic acid etc. may be responsible for it .
Eosinophilia – It can be defined as an increase in the relative or absolute number of eosinophils in the blood. Skin allergies , eosinophilic pneumonia, eosinophilic gastroenteritis , during estrus, parasites like filaria , hookworms, lungworms, strongyles , spirocerca, echinococcus , fascioliasis, trichinosis, fleas, hay fever, allergic bronchitis or sinusitis , food allergy , anaphylactic reaction , angioneurotic edema, drying – off period in cows, adrenocortical insufficiency , eosinophilic myositis, eosinophilic panosteitis, chronic suppurative diseases , eosinophilic leukaemia , after splenectomy etc. may be the few reasons of it .
Eosinopenia – It can be defined as the decrease in the total number of eosinophils in the blood below the normal range. It can be observed due to systemic stress , hyperadrenocorticism , administration of corticosteroids etc.
Basophilia – It can be defined as an increase in the relative or absolute number of basophils in the blood. Heartworms, chronic respiratory disease , hyperadrenocorticism with eosinopenia in dogs , basophilic leukemia, hypothyroidism etc.may be the reasons .
Basopenia – It can be defined as the decrease in the total number of basophils in the blood below the normal range.It is seen in dogs, cattle and horses when adrenal corticosteroids released in stress etc.
Lymphocytosis -It can be defined as an increase in the total number of lymphocytes in the blood above the normal range.It can be observed after vaccination , chronic infection , hypersensitivity , autoimmune disease, hypoadrenocorticism , lymphocytic leukaemia , lymphadenitis or lymphangitis ,infection with blood parasites like babesia , theileria, trypanosome etc.
Lymphopenia – It can be defined as the decrease in the total number of lymphocytes in the blood below the normal range.It can be seen due to conditions like chylothorax, chronic enteric disease , canine distemper , hog cholera , bovine viral diarrhoea , infectious canine hepatitis , corticosteroids , radiation , immunosuppressive drugs , hyperadrenocorticism, systemic stress etc.
Monocytosis – It can be defined as an increase in the total number of monocytes in the blood above the normal range. Corticosteroids, stress, chronic suppurative diseases , late phase of acute diseases , hemolytic anaemia, hemorrhage into the tissues, thrombocyte destruction , pyometra , retained placenta , exudate in pleural or peritoneal cavities , tuberculosis , brucellosis , systemic mycotic infections, protozoan infection etc. may be responsible for it .
Thus , by knowing the increase or decrease in the particular type of leucocytes , one can suspect the disease . Along with this the clinical signs should also be correlated and various other tests should also be done for the confirmatory diagnosis of the disease .
