Introduction
Disease:
· State of dysfunction of body systems.
· Deviation from normal healthy body condition.
· Inability of the body to perform physiological functions at normal level.
· Dynamic process developed in animal body as a result of interaction between causative agent and host.
Classification of Diseases:
· According to infectiousness:
1. Infectious disease: occur as a result of entrance, multiplication and activities of any infectious agents (virus, bacteria, Parasite and fungi) which cause pathological changes in tissues manifested by appearance of symptoms.
2. Non infectious disease: caused by any disturbance in normal metabolism, environmental conditions, trauma, physical and chemical agents or autoimmune disease.
· According to etiology (Cause):
1. Bacterial diseases: that caused by bacteria (Strangles, Glander, Tetanus, CL, Tuberclosis, Brucellosis, Leptospirosis, Clostridial diseases, ESD …..)
2. Viral diseases: that caused by viruses (Cattle Plague, FMD, LSD, Rabies, Canine Distemper, Camel Pox, AHS, VS, Canine Parvo, Feline Panleukopenia, RVF, ……)
3. Parasitic diseases: that caused by parasites
A) Trematodes (Fascioliasis, Paramphistomiasis)
B) Cestodes (Tape worm infestation mainly Anoplocephala perfoliata)
C) Nematodes (Verminous Pneumonia, Parasitic Gastroenteritis)
D) Protozoa (Babesiosis, Anaplasmosis, Trypanosomosis, Anaplasmosis)
E) Arthropods (Oestrus Ovis, Nasal Myiasis, Hypoderma bovis)
4. Fungal diseases: that caused by fungi (Ringworm, Canine Aspergillosis, Epizootic Lymphangitis, Mycotic Dermatitis, Dermatophytosis)
5. Multifactorial diseases: that caused by several infectious agents.
(Mastitis, Infectious Calf Diarrhea and Respiratory Disease Complex)
· According to Contagiousness (Transmissibility):
Transmissibility:
o Ability of pathogen to grow profusely and to be shed in large numbers in body fluid or excretions to infect or to be transmitted to a new host.
o Case with which disease is spread within populations.
1. Contagious diseases (communicable): in which infectious agents are transmitted from an infected animal, person, inanimate reservoir to susceptible host either by direct and/or direct contact.
(Brucellosis, Contagious bovine pleuropneumonia, FMD, CP, SGP, Dermatophytosis, Epizootic Lymphangitis, Coccidiosis, Mange)
2. Non-contagious diseases (Non-communicable): in which infectious agents transmitted only by indirect contact.
o AHS, BT à Need Arthropods (insect borne diseases)
o Tetanus à Need wound.
o Rabies à Need bite.
· According to Course (Duration)
Course: time from appearance of signs until end result of disease either recovery or death.
1. Peracute disease (form): that cause very rapid death within a few hours or 1:2 days due to septicemia (Anthrax, Clostridial diseases, Colibacillosis)
2. Acute disease (form): that cause severe infection and takes relatively longer course than per-acute form (few days or 1:2 weeks) as in ( CP – FMD – Salmonellosis)
3. Subacute disease (form): that takes longer course than acute form (few weeks to 1:2 months) as in (subacute form of AHS)
4. Chronic disease (form): that take very long course (fow months to 1:2 years) due to slow growth of the organism as in (Tuberculosis, CL, Johne’s diseas, Glanders)
· According to Occurrence (How disease occur) (Patterns of disease):
1. Sporadic disease: that occurs rarely in without regularity in a population.
(Tetanus, MCF, BVD, Blackleg)
2. Endemic disease (Enzootic): that occurs in usual frequency of occurrence in a population with predictable regularity and confined to certain locality or district as in Fascioliasis, FMD and LSD in Egypt.
According to fluctuation in predictable regularity classified into:
A) Mesoendemic. B) Hypoendemic. C) Hyperendemic.
3. Epidemic disease (Epizootic) (Oubreak): that occur in frequency higher (in excess of) than expected frequency as in (FMD, PPR, AI, Swine Influenza)
o Characterized by: rapid spread between animals & affect many animals
4. Pandemic disease: large scale epidemic which occur in many countries at same time.
5. Exotic disease: that occurs in a country which is previously free from it.
As in (Europe Origin à BVD, IBR, PI3, IPV, BL / Africa origin à AHS, RVF, BT, EI, LSD, CE, CBPP, PPR / Australia origin à BEF)
o Why (Factors facilitate entrance of exotic disease)
A) Importation of animals or animal products from infected localities.
B) Lack of quarantine measures.
C) Free Animal Movement between districts.
D) Lack of efficient laboratory skills.
o How to control of exotic disease
A) Prevent importation of animal or animal products from infected localities
B) Good quarantine measures.
C) Restriction of animal movement between districts.
D) Test and Slaughter of infected animals with hygienic disposal.
E) Vaccination of healthy in contact animals by inactivated vaccine (contraindicated to use live attenuated vaccine in free area بدخل المرض بايدي or in case of arthropod borne diseases because occur virulence reversion through arthropod which take blood meal from vaccinated animal then occur multiplication of infectious agent with production newly virulent agents which transmitted to animals again.
· According to species affected: (Multiple – Equine – Large ruminant – Small ruminant – Pet animal)
Common Terms used in infectious diseases:
1. Notifiable disease: that disease when appear in the field, the field and or owner must immediately notify about it to local authorities to:
ü 1- Establish all precautions and measures for protection of both human and animal health.
ü 2- Take all measures to confirm diagnosis.
ü 3- Undertake quarantine and other control measures.
Ø Characterized by: Rapid spread – Zoonotic importance – high economic loss
Ø Examples: Anthrax – Rabies – Brucellosis – TB – FMD – CP – Glanders – AHS – EI – Horse Pox – MCF – EE
2. Zoonotic disease: that transmitted to human being by direct or indirect methods (TB, Brucellosis, Leptospirosis)
3. In-apparent infection: infection of susceptible animals without appearance of any clinical signs although infectious agent take the same course of the disease to produce signs (ie: multiply, replicate and shed from animal) so cause considerable problem in disease control
ü It can be demonstrated only by lab method.
4. Latent infection: it is an in-apparent infection but causative agent has ability to produce signs of disease under stress factors
OR causative agent present inside body but undetectable and under stress factors become detectable and produce clinical signs.
Or infection that persist inside animal body without producing clinical signs, Once stress factors present the causative agent produce clinical signs.
Example: Black disease (CL.Novyi and Fasciola relationship)
5. Reservoir: Normal inhabitant of causative agent (animal, plant, snail, soil or inanimate object) in which agent lives, multiply and transmitted to susceptible host.
6. Carrier animal: apparent healthy animal (in-apparent infected animal) that shed micro-organism without showing any clinical signs and it can be diagnosed only by lab methods
ü Most clinical cases remain carrier after recovery.
ü Classification according to stage or time of shedding of micro-organism:
ü 1- Incubatory carrier (Preclinical): shed micro-organism during incubation period of disease as rabid animal shed rabies virus in saliva 3:5 days before appearance of clinical signs.
ü 2- Convalescent carrier: shed micro-organism during convalescent period and this animal is clinically cured but not bacteriologically cured as FMD
ü Classification according to duration of carriage:
ü 1- Temporary carrier: carry micro-organism for days, weeks or months.
ü 2- Chronic carrier: carry micro-organism for years or long life
7. Incubation Period (IP) for virus and bacteria = Pre-patent Period for parasites: time elapsed between entrance of infectious agent till appearance of clinical signs
Pre-patent Period: The time elapsing between the initiation of a parasite's infection of a definitive host and the appearance of the products of parasite reproduction, e.g., eggs, larvae, etc.
8. Latent Period: The time from initial infection until the start of infectiousness.
9. Course:
10. OIE (Office International des Epizooties) (The World Organization for Animal Health): it is an office or organization gives full epidemiological data about any disease all over the world.
OIE classify diseases according to severity into:
ü 1- List A: group of diseases which characterized by:
o Rapid spread
o Sever socioeconomic loss
o Zoonotic importance
o Major importance in international trade of animal and animal byproducts
o Scope of which extend beyond borders (TADs)
o Examples: LSD – FMD – PPR – CP – RVF – AHS – AI – SGP – BT
ü 2- List B: group of diseases which characterized by:
o Socioeconomic loss and/or zoonotic importance.
o Major importance in international trade of animal and animal byproducts
o Examples: Brucellosis – Anthrax – TB – Leptospirosis – Babesiosis – Theileriosis – Trypanosomiasis – Mange – EI – EE – EVR – EVA – Glanders – MCF
ü 3- List C: group of diseases which characterized by:
o Socioeconomic importance
o Example: Blackleg – Listeriosis – Toxoplasmosis – Fascioliasis
11. Trans-boundary animal diseases (TADs): group of highly contagious epizootic diseases that transmitted across national borders and characterized by:
ü 1- Rapid spread
ü 2- Socioeconomic loss
ü 3- Public health importance
ü 4- High morbidity and mortality rate
Examples: List A of OIE
12. Early Warning System (EWS): System used for early detection of disease through early diagnosis by studying of all epidemiological and predisposing factors of disease.
ü Early detection of microbial circulation prevent spread of the disease to other animals and to human
13. Biosafety (Biosecurity): Number of measures which applied to:
ü 1- Reduce onset of disease
ü 2- Prevent spreading of disease
ü 3- Prevent disease causing agent from entering or leaving any place
14. Epidemiology (Epizootology):
ü Definition: Science which deals with studying of health and disease state within population and involve: بمعني اخر و هو تجميع معلومات عن المرض و تفسير هذه المعلومات
Ø 1- Determine all factors of etiology
Ø 2- Establishment of the disease
Ø 3- Distribution and spread of the disease.
Ø 4- Animal susceptibility
Ø 5- Factors affect economic importance of disease
ü Aim:
Ø 1- Determine extent and location of problem.
Ø 2- Determine animal susceptibility to disease.
Ø 3- Determine time of outbreak as some diseases have seasonal incidence as LSD in summer while Strangles in winter.
Ø 4- Identify etiological agents of diseases and their distribution within population.
Ø 5- Establishment of good control measures.
15. Epidemiological Triangle (Disease Determinants): factors contributing occurrence of disease and include: Infectious agent – Susceptible animal – Suitable environment
16. Mode of transmission (Mode of spread): Mechanism by which infectious agent transmitted from reservoir or carrier animal to susceptible animal
Ø Types:
o Horizontal Transmission: infectious agent transmitted from any segment of population to another either directly or indirectly
§ 1- Direct: susceptible animal contract infection by:
A. Direct contact with infected animal through touch, scratch, bite or intercourse.
B. Contact with host infected discharges as feces, urine or droplet which spread onto conjunctiva or mucous membrane of eye, nose or mouth during coughing or sneezing.
§ 2- Indirect: involve intermediate link between infected and susceptible host.
A. Vehicle borne transmission: through exposure to contaminated inanimate object (surgical materials, soil, water, food) or biological material (blood, serum, vaccine, plasma) and infectious agent might or might not developed in or on vehicle before transmission.
B. Vector borne transmission: through invertebrate vectors (flies, mosquitoes or ticks) either mechanically (without development of agent as VS) or biologically (with development of agent as RVF, Babesia)
C. Air borne transmission (Aerosol): agents aerosols are suspensions of particles in air which remain suspended in air for long period and infect susceptible animal through respiratory tract
May be (Droplet or Dust infection)
o Vertical Transmission: infectious agent transmitted from animals of one generation to subsequent generation and may be: trans-ovarian as babesia between generation of tick, trans-placental (in-utero) as BVD or BL or Trans-colostral as Ascariasis.
17. Mode of infection (Routes of infection) (Portals of entry and exit): the way(s) by which infectious agent gains entry to body of susceptible animal and by which leaves host and include: alimentary, udder, anal, skin, respiratory, urogenital and conjunctiva.
18. Signs: Objective evidence of the disease which detected by examiner as lameness
19. Symptoms: Objective or Subjective evidence of disease and may be
A. Generalized: which present in most of cases and not specific to certain disease (fever, anorexia, depression,….)
B. Objective (Signs): which observed by examiner as lameness
C. Subjective: which confined to patient as colic
D. Specific symptoms: which specify certain disease and not present in other diseases as locked jaw in case of tetanus, abscessiation of sub-maxillay lymph nodes in case of strangles and escape of unclotted blood form body orifices in case of Anthrax
20. Disease Control: all procedures or measures aimed to reduce disease frequency
A. If animal diseased by exotic disease or notifiable disease à slaughter all infected animals and hygienic disposal.
B. If animal disease by endemic disease à treatment and quarantine measures.
C. Healthy animal à Immunization
21. Disease eradication: all procedures or measures aimed to completely eliminate disease from an environment as in case of exotic or notifiable diseases.
22. Quarantine: period of time during which an animal’s movement is restricted (3-5 weeks) and tested and observed for evidence of disease to:
A. Prevent inter-herd transmission of disease
B. Prevent entrance of exotic and epidemic diseases
23. Diagnosis: Studying methods for recognizing of disease by field investigations and recent lab procedures
24. Prognosis: end result of disease, outcome of disease or prediction of future of disease and it may be good or bad (favorable or unfavorable)
25. Case: Individual animal infected by infectious disease
26. Infective period: longest period of disease during which affected animal act as a source of infection.
27. Pathological material: Samples obtained from dead or live animal contain or suspected to contain infectious agent to be sent to lab.
28. Vaccination: Introduction of vaccine into animal body to produce immunity against specific disease.
29. Vaccine: Suspension of live attenuated or inactivated or killed micro-organism or its products which given in a routine manner for prevention or control infectious disease.
Aim: 1- Prevent disease
2- Decrease number of susceptible animal during outbreak using emergency vaccination