4 avcn 15-21.pdf

Anthrax An infectious disease of warm-blooded animals (as cattle and sheep) caused by a spore-forming bacterium (Bacillus anthracis), transmissible to humans especially by the hand[r]

UNIT 4 DISEASE - GENERAL PRINCIPLES

1 Reading

What it is and its causes Disease, in a general sense, can be said to be a deviation from the normal conditions of an animal It can also be said to mean a change in the normal condition of

an animal caused by a living organism and this is the meaning more generally given to it

Diseases caused by living organisms are called infectious and all of them can be spread from animal to animal Those transmitted by direct or indirect contact are sometimes called contagious Diseases spread by insects or other vectors are called non- contagious

Living organisms which may infect the body and cause disease include: (i) Bacteria

These are small organisms generally visible under the ordinary microscope and termed cocci (round or oval in shape); bacilli (rod shaped); or spirilla (long cells twisted into spirals) Bacteria also include organisms called rickettsia which (like viruses) can multiply only in living cells

(ii) Viruses These are so small that they can only be seen under a special, very high-powered microscope Examples of the diseases they cause are rinderpest, African swine fever, and foot and mouth disease Viruses can be transmitted by small flying insects, examples of the diseases caused in this way are blue tongue and three day sickness

(iii) Protozoa These organisms are normally larger than bacteria and can clearly be seen under the ordinary microscope An important difference between protozoa and bacteria is that

in the case of many of the diseases caused by protozoa, the protozoan organisms concerned undergo part of their reproductive cycle in an intermediate host such as a tick

or fly These diseases are of special importance in tropical and sub-tropical areas

Some diseases caused by protozoa have no intermediate host such as the ticks or tsetse flies mentioned above but are passed directly or indirectly (by mechanical carriers) to a final host

(iv) Parasites This is a very important group of organisms from the animal kingdom which live (or are parasitic) in or on other organisms or animals which are referred to as the "hosts" These parasitic organisms are referred to as ecto-parasites when they live on the outside of animals (ticks, mites, fleas and lice) and endo-parasites when they live inside the animal (flukes, flat-worms and round-worms)

(v) Fungi The fungi are microscopic and some of them cause disease, ringworm being an important example of such a fungus

Non-infectious conditions Non-infectious diseases (caused by factors other than living organisms) include those resulting from a low level of nutrition (especially from a lack of vitamins or mineral); mechanical injuries and lesions such as cuts, abscesses, ulcers and fractures; poisoning; hereditary conditions transmitted through the parents; excessive heat or cold; an insufficient

or excessive production of hormones; tumors and certain disease conditions such as milk fever in dairy cattle

Predisposing causes These are causes of disease which open up or prepare the way for specific diseases Such causes include: the age of the animals; climate and weather conditions, which may result in animals being exposed to heavy rain or severe cold, or tropical conditions of sun and heat and which may reduce the natural resistance of the animals to disease; pollution

of water and air; poor feed such as moldy hay and green crops causing "bloat"; excessive work; hereditary conditions handed down through parents and certain disease conditions

Morbidity and mortality These terms are frequently used in describing the results of disease in a herd or flock Morbidity is the number of animals in a herd or flock which are affected by the disease but which do not die If a large percentage of the animals become affected the morbidity is said to be high Mortality is the number of animals dying from disease

Both mortality and morbidity are generally expressed as a percentage, e.g 10 animals affected out of 100 would be 10 percent

Epizootic, enzootic and sporadic diseases Epizootic is the term used to denote a disease of animals (such as rinderpest) which spreads rapidly over a large area It corresponds to the word epidemic which is used to describe a disease which rapidly spreads amongst human beings

Enzootic is the term used to describe a disease which is continuously present in a population of animals but does not spread rapidly like an epizootic

Sporadic is used to refer to a disease not normally present in an animal population but which appears suddenly from time to time and, equally suddenly disappears

Immunity, tolerance and susceptibility When an infectious disease invades an animals body the animal may develop the ability to resist it, in which case it is said to have immunity to the disease The substances produced in the body which help the animal to resist disease are called antibodies

Immunity of an animal to disease varies greatly from one disease to another If the animal can resist the disease without having been vaccinated against it, the immunity is termed

"natural immunity" If, however, the animal has been given vaccine against the disease, its immunity is termed "artificial immunity"

Tolerance is a form of resistance against disease acquired by animals of an animal population which have been in contact with a disease for many generations The N'Dama cattle breed of West Africa is the prime example of this The animals of this breed have a much higher degree of resistance to trypanosomiasis than breeds of cattle having had no contact with the disease

An animal is said to be susceptible to disease when it has no immunity, tolerance

or resistance to the disease and goes down with the disease on exposure to it

Sanitation

An important means of preventing and controlling disease is the maintenance of good animal hygiene The severity of some diseases is dependent on the number and virulence of microorganisms entering the animal's body Many microorganisms live and multiply outside the animal, so the number of microorganisms can be reduced by

implementing sanitation practices These practices, in turn, reduce the incidence of disease outbreaks

Manure and other organic waste materials are ideal environments for the proliferation of microorganisms A good sanitation program includes cleaning of organic materials from buildings, pens, and lots This allows the effective destruction of microorganisms from high temperatures and drying Buildings, pens, and pastures should be well drained, preventing prolonged wet areas or mud, holes These sanitation practices help both in disease prevention and controlling parasites

Antiseptics and disinfectants are carefully selected and effectively utilized in a good sanitation program Antiseptics are substances, usually applied to animal tissue, that kill or prevent the growth of microorganisms Disinfectants are products that destroy pathogenic microorganisms They are usually agents used on inanimate, objects In the absence of disinfectants, sanitizing with clean water is helpful

If a herd or flock becomes infected with disease it is very important to remove the infected animals to a place where they are isolated from other stock In some cases it may

be better to isolate all the healthy animals Animals isolated in this way should be herded and looked after by herdsmen who have nothing to do with other stock or the herdsmen of other stock

In outbreaks of disease the veterinary services of a country will often declare an area

to be "in quarantine" This means that the movement of animals is restricted to a certain designated area laid down by the veterinary authorities

The A.H.A can play an important part in this not only in supervising the animals and herdsmen involved but in convincing the local stock-owners of the necessity for such a measure

Other measures which should be taken in preventing the spread of infection include the destruction of carcasses by fire and their disposal by burial; the disinfection of buildings and pens where practical, and, where grazing lands are heavily infested by parasites These measures are generally best planned by the veterinary officer

2 Pronounciation

SOME MAJOR DISEASES OF FARM ANIMALS

Acetonemia An abnormal increase of ketone bodies in the body in

conditions of reduced or disturbed carbohydrate metabolism (as in uncontrolled diabetes mellitus) Actinomycosis Infection with or disease caused by actinomycetes ;

especially : a chronic disease of cattle, swine, and humans characterized by hard granulomatous masses usually in the mouth and jaws

Anthrax An infectious disease of warm-blooded animals (as cattle

and sheep) caused by a spore-forming bacterium (Bacillus anthracis), transmissible to humans especially by the handling of infected products (as hair), and characterized

by external ulcerating nodules or by lesions in the lungs Atrophic rhinitis: A chronic disease of swine that is characterized by

purulent inflammation of the nasal mucosa, atrophy of the nasal conchae, and abnormal swelling and distortion of the face

Aujeszky’s disease A disease primarily of pig but can occur in other secondary

host species; caused by herpesvirus and characterized by respiratory, reproductive, and nervous signs

Avian influenza Any of several highly variable diseases of domestic and

wild birds that are caused by orthomyxoviruses and characterized usually by respiratory symptoms but sometimes by gastrointestinal, integumentary, and urogenital symptoms — called also fowl plague

Babesiasis Infection with or disease caused by babesias — called also

babesiasis Botulism Acute food poisoning caused by botulinum toxin

produced in food by a bacterium of the genus Clostridium ( ) and characterized by muscle weakness and paralysis, disturbances of vision, swallowing, and speech, and a high mortality rate

Bovine spongiform encephalopathy

Brucellosis Classical swine fever

Coccodiosis Colibacillosis

Enzootic pneumoniae

Erysipelas

Foot and mouth disease

Infectious bursal disease (Gumboro disease)

Japanese encephalitis

Leptospirosis

Milk fever

A progressive fatal disease of the central nervous system of adult domestic cattle that resembles scrapie of sheep and goats and is prob Caused by a prion transmitted by

infected tissue in food — abbreviation bse; called also mad cow disease

A disease caused by bacteria of the genus Brucella — called also Malta fever

Also hog cholerae, a highly infectious disease of pigs caused by a togavirus and characterized in its classical form by high fever, lassitude, purple discoloration of abdominal skin, conjunctivitis and nervous signs including circling, incoordination, tremor, and convulsions

Infestation with or disease caused by coccidia Infection with ; takes many forms, some of them septicaemia, some toxigenic due to absorption of the

enterotoxin and some locally toxigenic due to the effects of the bacteria’s endotoxin

A group of pneumonic diseases which affect young animals They are principally viral origin, although mycoplasmas also play a part, and are only mild pathogenic unless secondary bacterial invasion intervenes

rarely in cattle and sheep, mainly in pigs which are marked by diamond-shaped skin lesions

An acute contagious febrile disease especially of cloven- hoofed animals that is caused by any of several

picornaviruses (genus Aphthovirus) and is marked by ulcerating vesicles in the mouth, about the hooves, and on the udder and teats

A disease of 3-6 week chickens caused by Binavirus which primarily and selective destroys B lymphocytes in the bursa of Fabricius resulting in a secondary

immunodeficiency

An encephalitis that occurs epidemically in Japan and other Asian countries in the summer, is caused by a

flavivirus (genus Flavivirus) transmitted by mosquitoes (especially Culex tritaeniorhyncus), and usually produces a subclinical infection but may cause acute

meningoencephalomyelitis Any of several diseases of humans and domestic animals (as cattle and dogs) that are caused by infection with spirochetes of the genus Leptospira — called also lepto

A disease of newly lactating cows, sheep, or goats that is

caused by excessive drain on the body mineral reserves during the establishment of the milk flow

Neoplasms Newcastle disease

Parakeratosis Pasteurellosis PRRS Rabies

Rinderpest

Salmonellosis

Swine dysentery Trichinellosis

White muscle disease

A new growth of tissue serving no physiological function : TUMOR

A disease of domestic fowl and other birds caused by a paramyxovirus (genus Rubulavirus) and resembling bronchitis or coryza but in later stages distinguished by nervous invasion leading to incoordination, tremors, and twitching of the head and being especially destructive of young birds although all ages may be attacked

An abnormality of the horny layer of the skin resulting in a disturbance in the process of keratinization

Infection with or disease caused by bacteria of the genus Pasteurella

Porcine reproductive and respiratory syndrome

An acute virus disease of the nervous system of warm- blooded animals that is caused by a rhabdovirus (genus Lyssavirus) transmitted with infected saliva usually through the bite of a rabid animal and that is typically characterized by increased salivation, abnormal behavior, and eventual paralysis and death when untreated

An acute infectious febrile disease of ruminant animals (as cattle) that is caused by a morbillivirus and is marked by diarrhea and inflammation of mucous membranes Infection with or disease caused by bacteria of the genus Salmonella typically marked by gastroenteritis but often complicated by septicemia, meningitis, endocarditis, and various focal lesions (as in the kidneys)

A disease characterized by severe diarrhea with passage of mucus and blood and usually caused by infection

Infestation with or disease caused by trichinae contracted

by eating raw or insufficiently cooked infested food and especially pork and marked initially by colicky pains, nausea, and diarrhea and later by muscular pain, dyspnea, fever, and edema

A disease of young domestic animals (as lambs and calves) that is characterized by muscular degeneration and is associated especially with inadequate intake of vitamin E