3. Diagnosis of infectious diseases, treatment of animals having infectious diseases.

Question 1

Diagnostics of Infectious diseases?

Answer 1

Diagnostics of infectious diseases

• Complex procedure: lab d alone is not enough!
• Epidemiological data: vet must perform
• Clinical signs: allergic reactions
• PM lesions
• Preliminary diagnosis: local vet ʹ Diff Dx, make list of what it could be to narrow down
• Lab exam (diagnostic institutions) ʹ aimed diagnosis by referred vet
• Sampling: appropriate number, how to sample correctly & covering letter
• Clinical observations & necropsy
• Histological examination

Question 2

Direct detection of the agent: Agent itself?

Answer 2

Direct detection of the agent: Agent itself

• Microscopic examination (organs, fluids: stain with Gram bacteria: smear)
• (Electron microscopic exam) (detection of viruses mainly) ʹ better ways available now (Not used frequent as its expensive)
• Isolation (medium ʹ cell culture ʹ egg ʹ laboratory animal): good for bacterial, can
• do for viruses but uses molecular methods more nowadays
• Detection of antigens (immunofluorescence, ELISA, western/immunoblot, electrophoresis)
• Methods detecting nucleic acids (DNA hybridisation, PCR: Ricketsia, Mycoplasma,
• can detect some genes for virulence factors

Question 3

Indirect detection of the agent? ( Serological and Cellular tests)

Answer 3

Indirect detection of the agent:

• Antibodies,
• immune cellular reactions

Serological tests

• Classical: agglutination, precipitation, electrophoresis, PAGE, Complement fixation
• Virus serology: Virus Neutralisation, HAI Haemagglutination inhibition (Infl, Parainfl)
• Marked (mostly used now!) immunological methods: IF, ELISA, (RIA & IRMA
• need isotypes) (ELISA is very good)

Cellular tests:

• not as widely used for diagnosis, not easy to read them
• Lymphocyte stimulation test: LST - paratubercuolosis
• Immune rosette formation
• Allergic tests: Tuberculin
• Cytotoxic reaction
• Macrophage migration (not widely used)
• Gamma interferon test - mycobacteria

Question 4

Characteristics of the Lab diagnostic test?

Answer 4

Characteristics of the lab diagnostic test

• Sensitivity (97%): can detect large number of positive cases
• specificity (there should not be cross reactions): when detect positive, that they are actually positive and not false
• Want a test with Good specificity & sensitivity
• Influenced by:
• amount & antigenicity of the agent, phase of the pathogenesis
• Indirect: needs time for the immune reaction, so can’t be used in acute phase of pathogenesis,
• but can be used even after clinical signs disappear So:
• More diagnostic methods have to be used AND they have to evaluated together with the pathogenesis/Clinical signs/PM lesions
• complex final evaluation
• None of them are 100%, there are always mistakes
• Evaluation of data, diagnosis

Question 5

Treatment of diseased animals?

Answer 5

Treatment of diseased animals

• Aetiological treatment
• Bacteria (own metabolism): AB treatment (appropriate medicine ʹprudent use!)
• Hyper-immune serum: animals vaccinated many times producing high level of
• antibodies then the blood is taken and the serum from them is used to treat other animals with their serum ʹ not widely used
• Viruses: antiviral medicines (limited use, very expensive, have to be used in the
• appropriate phase of the pathogenesis)
• Symptomatic treatment : support the healing/immune system of the animals
• animal welfare
• Individual/mass treatment
• Treatment of certain diseases is not allowed e.g. TB, Malleolosis (prohibited to treat
• Some chronic diseases cannot be treated or treatment is not reasonable e.g. fowl/swine typhoid (easier to slaughter than to treat)
• Prevention of complications (diseases caused by viruses) ʹ can give ABs to treat
• viruses e.g. IBR to avoid secondary complication/infection due to bacteria
• o Elimination of predisposing factors helps recovery (environmental factors)