Infectious process

Content
Infectious diseases. Infectious process
Biological basis of infectious process
Syndromes of infectious diseases.
Diagnosis (etiology)
Microscopy,
Bacteriological investigation ,
Serological investigations
Primary and secondary immune response
To prove etiological diagnosis: Ab; Ig; Ag
Phases of the process
Treatment
Etiotropic treatment
Pathogenetic (syndromic) treatment
Basic regiment

Infectious PROCESS is
an interaction between
micro- and macro-organisms
(under the impact of natural and social factors of the environment).
Infectious DISEASE is
a clinically marked part of this process.

Infectious diseases
There is an agent =>
Contagious: can be transmitted to another macro-organism => possibility of an outbreak.
Cyclic course (timing).

Infectious process.
got
inf.
Disease:
Severe. Moderate.
Mild. Sub-clinical.
Carriage.
incub
relapse
Clinical recovery:
sanitation or chronic form
onset

Biological basis of infectious process
Agent’s factors:
pathogenic power; portal of entry of infection; dose
Host’s factors:
genetically determined: non-specific
and specific resistance (HLA)
acquired: nutrition, intoxications, ecologic factors, behavior patterns, vaccination, treatment.

Complications
Specific: typical to the disease (perforation of ulcers of small intestine in typhoid fever patients)
Non specific (sepsis of another origin due to prolonged presence of intravenous catheter).

Symptoms and signs of infectious diseases
Fever
Rash
Lymphadenopathy
Liver /spleen enlargement
Respiratory syndrome
Diarrhea
Hepatitis
Meningeal syndrome, etc

Syndromes
Congunctivitis,
Tonsillitis, pharyngitis, stomatitis, …
Pneumonia, bronchitis…
Gastro-entero-colitis…
Hepatitis…
Kidney insufficiency (acute, chronic)
Meningitis…
DIC,
etc

Diagnosis
Anamnesis, symptoms and signs => syndromes.
Prove the syndrome: biochemical tests, ECG, X-ray, USI, etc.
Anamnesis, association of syndromes => suggestion of etiology.
Clinical etiologic diagnosis is always hypothetical => how to check it?

Etiologic diagnosis
To prove or to disapprove it: to find the supposed agent or to find its markers.
Markers: Ag of the agent or Ab to it.
Methods depend on the agent:
bacteria, virus, rickettsia, clamydia, mycoplasma, protozoa, helminthes, fungi.

Microscopy
Pluses:
- fast
- the main method for protozoa, helminthes, fungi.
Minuses: for bacterial infections in the most cases it is a tentative method.
But sometimes can be very informative (N.meningitidis in CSF).

Bacteriological investigation
Pluses: accurate; sensitivity to antibiotics
Minus: needs time (several days or more)
Negative result does not always turn down a supposed diagnose:
- defects of sample taking, transportation, media and lab technique;
- recovery stage (spontaneous or due to correct treatment).
Absence of correct suggestion! => media

Serological investigations
To detect antibodies to a suggested agent
Antibodies – in serum (CSF).
Pluses: simple; reliable; cheap; often – the only confirmation of a diagnosis.
Minuses:
“window period”;
investigation itself is fast, but results are always retrospective.

Primary
immune response
Onset
10
“Window”
period
20
IgG
IgM
Antibodies
30
40

Secondary
immune response
Onset
10
No “window” period; no IgM
20
IgG
only
Antibodies
30
40

To prove etiological diagnosis: Ab
4 times increase in titers of Ab to the agent (primary or secondary immune response):
Samples should be taken twice in time!
- 1-st time: the 1-st week (zero is expected),
- 2-nd time: in 2 weeks (maximum level).
Diagnosis is late: after 2-3 weeks; can be even later under effective treatment =>
- the 3d sample at week 5-6 of the disease.
The only test can be (+) due to previous disease, vaccination, poly-agglutination. “Min diagnostic level of Ab” is not reliable.

To prove etiological diagnosis: Ig
Ig M (+) to the agent even once means
the primary immune response.
Ig M can be usually found since the 5-th day of the disease up to the 4-6 weeks.
Rare IgM can persist much longer (HBV).
Ig G(+): >10 days of the disease (peak, recovery, chronic stage, previous disease or vaccination)–similar to Ab significance.

To prove etiological diagnosis: Ag
Ag can be found in any substrate.
No “window” period =>
- Express-techniques to reveal the Ag (Ab with some additional mark to make immune complex visible): plague, etc.
PCR – to reveal DNA/RNA of the agent. In blood PCR(+): replication; PCR(-): no replication; sanitation -? => biopsy.
Ag disappear in the process of sanitation in recovery stage => Ab.

Phases of the process
The end of incubation and the first part of the disease – presence of Ag; no Ab: the most contagious and dangerous part.
Recovery with clearing from the agent: all Ag disappear, Ab become (+).
Chronic form: presence of Ag, or Ag+Ab; sometimes – only Ab (anti-HBcor Ab).
Life prognosis depends mostly on tissues functions (biochemical tests, ECG, etc).

Mixed infections,
combination of different diseases
Confirmation of the one disease does not allow us to exclude another one.
To exclude (or confirm) a disease we should investigate for this disease.

C
B
D
inf
1
2
3
4
5
6
7
8

Exact diagnosis:
Prognosis
spontaneous course (subclinical, mild, moderate, severe),
under the treatment
Treatment
etiology,
phase of the process,
severity

Infectious process.
got
inf.
Disease:
Severe. Moderate.
Mild. Sub-clinical.
Carriage.
incub
relapse
Clinical recovery:
sanitation or chronic form
onset

Treatment
Etiotropic – to affect the agent.
Pathogenetic (syndromic)– to improve or to replace tissues functions.
Symptomatic – to suppress symptoms.

Etiotropic treatment
Antibacterial, antiviral, antiprotozoal, etc.
Result of therapy depends mostly on
- correct choice of spectrum and activity of preparations (if not correct: disease and treatment go own ways);
when the treatment is started (the first 1-2 days => just stop the disease);
duration of the treatment.

Pathogenetic (syndromic) treatment
Can be life-saving (rehydration in cholera, hemodialysis in HFRS, dehydration in brain edema, intubation in laryngeal diphtheria).
Often it is the main part of the treatment: DS is too late to start etiotropic treatment (HAV, HF), or etiotropic treatment is not correct, etc.

Basic regiment
Bed rest
Diet: in acute diseases – according to appetite; boiled and cultured milk foods can be used in any situation. Liquids.
Clinical observation (behavior, t, pulse, BP, RR, diuresis, symptoms and signs).
Symptomatic treatment - can be useful.