Introduction to the infectious disease, how they transmitt and the stratigies used for the management of infectious disease because it's more in tropical and subtropicals

2. • ‘Infection’ is defined as the process of foreign organisms
invading and multiplying in or on a host.
• Infectious diseases remain the main cause of morbidity
and mortality in man, particularly in developing areas.
• Infectious agents:
1. Prions.
2. Viruses.
3. Bacteria.
4. Eukaryotes (protozoa, helminthes, and fungi).

3. • Host–organism interactions:
• Each of us is colonized by huge numbers of microorganisms
(1014 bacteria, plus viruses, fungi, protozoa and worms),
with which we coexist.
• The relationship with some of these organisms is symbiotic
(in which both partners benefit), while other organisms are
commensalism (living on the host without causing harm).
• Infection and illness may be due to these normally
harmless commensalism and symbioses evading the body's
defenses and penetrating into abnormal sites.
• Alternatively, disease may be caused by exposure to
exogenous pathogenic organisms that are not part of our
normal flora.
• The symptoms and signs of infection are a result of the
interaction between host and pathogen.

4. Routes of transmission:
1= Endogenous infection:
• The body’s own endogenous flora can cause infection if the
organism gains access to an inappropriate area of the body.
2= Air-borne spread:
• Many respiratory tract pathogens are spread from person to
person by aerosol or droplet transmission.
3= Faeco-oral spread:
• Transmission of organisms by the faeco-oral route can occur
by direct transfer (usually in small children), by contamination of
clothing or household items (usually in institutions or conditions
of poor hygiene) or most commonly via contaminated food or
water.
4= Vector-borne disease:
• Many tropical infections, including malaria, are spread from
person to person or from animal to person by an arthropod
vector.

5. 5= Direct person-to-person spread:
• Organisms can be passed on directly in a number of ways. E.g
(Sexually transmitted infections, Skin infections, blood to blood
transmission).
6= Direct inoculation:
• Infection can occur when pathogenic organisms breach the
normal mechanical defences by direct inoculation.
• May be inoculated by accident, e.g (tetanus, fungi, and rabies).
7= Consumption of infected material:
• Food-related zoonotic infections are due to contamination of
food with animal faeces, several diseases are transmitted
directly in animal products. These include some strains of
Salmonella (eggs, chicken meat), brucellosis (unpasteurized
milk) E. coli and the prion diseases kuru and vCJD (neural
tissue).

6. Prevention and control:
Infection control measures:
• Wash or clean hands.
• Wearing medical equipment and devices.
Eradication of reservoir:
• Treatment and immunization.
Immunization.

7. • Healthcare-associated infections:
• Clostridium difficile, Staph. aureus (especially MRSA),
vancomycin-resistant enterococci, multiresistant,
Gram-negative organisms are all strongly associated
with healthcare contact and are a growing problem
in hospitals worldwide.
• HCAI control measures:
A. Hand hygiene.
B. Personal protective equipment.
C. Aseptic technique.
D. Urinary catheters.
E. Vascular access devices.

8. Classification of outbreaks:
• Person to person:
• Where infection is passed from one infected individual to another and
outbreaks of infection are separated by the incubation period.
• Point source:
• Is where there is a single source of infection, e.g. food eaten at a social
function.
• Common source:
• Where there is a single source of infection but over a period of time, e.g.
a symptomatic carrier of infection working with food preparation.
• Epidemic:
• An increased unusual widespread infection in the community, causing
waves of infection.
• Pandemic:
• Is an epidemic occurring worldwide or over a very wide geographical area
and crossing international boundaries, usually affecting a large number of
people e.g COVID 19.

9. PRINCIPLES AND BASIC MECHANISMS:
o Specificity:
• Microorganisms are often highly specific with respect to
the organ or tissue they infect. E.g hepatotropic viruses are
{hepatitis A, B, C and yellow fever}.
o Pathogenesis:
• Is the process by which infectious agents can cause
disease.
• Steps following pathogenesis:
1. Epithelial attachment.
2. Colonization.
3. Tissue dysfunction or damage:
A. Cell lysis
B. Exotoxins and endotoxins.

10. Pathogen entry
Epithelial Attachment
Or inoculation
Multiplication
Colonization
Tissue invasion
Luminal/superficial
epithelial infection e.g
(V. cholerae, T.
vaginals,
Dermatophytes)
Intracellular e.g
(Virus, Toxoplasma)
Extracellular e.g
(Staphylococcus spp
E. histolitica)
Circulation
(blood/lymph) e.g
Plasmodium spp
Filariasis.
Bacteraemias.
Cell/tissue injury
Dysfunction e.g
Enterotoxin ( V.
cholerae, E. coli
Destruction e.g
Cytotoxin (
Diphtheria,
Gas gangrene)

11. Protein secretion pathways for Gram-negative bacteria. These specialized pathways are
necessary for virulence. Types I and II facilitate protein (toxin) secretion into the
extracellular space (type I). Type II does this in two stages. Types III and IV pathways
secrete toxins, as well as injecting toxins directly into the host cells via multiprotein
complexes across the bacterial cell envelope and host-cell membrane. Type V is a minor
variation of type II. The type VI pathway is unclear but is involved in cytotoxicity.

12. • Host response to infection:
• Natural defences:
• Intact surface epithelium, local secretion,
antimicrobial enzymes and gastric acidity.
• Immunological defences:
• Antibody- and cell-mediated immune mechanisms
play a vital role in combating infection.
• Metabolic and immunological consequences:
1. Fever.
2. Inflammatory response.

13. Clinical Approach to the Patient with a Suspected
Infection:
Fever:
• Is often regarded as the cardinal feature of infection.
• Fever is usually intermittent, may not be present at the time of
presentation and occurs less commonly in elderly patients.
• Infection can also present with hypothermia (temperature
<36°C), which is a poor prognostic sign.
Physiological assessment:
• Patients should initially be assessed according to the airway,
breathing, circulation, disability and extremities (ABCDE)
approach.
• Evidence suggesting sepsis or septic shock should be sought.
Diagnostic assessment:
• History-taking and examination should aim to identify the site
of infection and also the likely causative organism.

14. A) History:
• A detailed history is taken with specific questions about
symptoms and epidemiological risk factors for infection.
The latter are based on sources of infection and routes of
transmission.
• Symptoms, Travel history, Food and water history,
Occupational history, Animal contact, Sexual activity,
Intravenous drug use and Vaccination history.
B) Clinical examination:
• A thorough examination covering all systems is required.
• Skin rashes and lymphadenopathy are common features of
infectious diseases and the ears, eyes, mouth and throat
should also be inspected.
• Rectal, vaginal and penile examination is required in
sexually transmitted infections.
• The fever pattern may occasionally be helpful: for example
the tertian fever of falciparum malaria.

15. Infections commonly associated with a
rash:

16. Investigation:
• In some infections, such as chickenpox, the clinical presentation
is so distinctive that no investigations are normally necessary to
confirm the diagnosis.
A) General investigations (to assess health and identify organ(s)
involved):
• Blood tests
Routine blood count, ESR and C-reactive protein (CRP),
biochemical profile, urea and electrolytes are performed in the
majority of cases. Procalcitonin may be a more specific marker
of bacterial infection but it seems to be controversial.
• Imaging
X-ray, ultrasound, echocardiography, computed tomography
(CT) and magnetic resonance imaging (MRI) are used to identify
and localize infections. Positron emission tomography (PET) and
single photon emission tomography (SPECT) have proved useful
in localizing infection, especially when combined with CT
scanning.

17. • Radionuclide scanning
After injection of indium- or technetium-labelled white cells
(previously harvested from the patient) occasionally helps to
localize infection. It is most effective when the peripheral white
cell count is raised and is of particular value in localizing occult
abscesses.

18. B) Microbiological investigations (to identify causative organism):
• Direct tests
Some microbiological tests rely on direct examination of a tissue
specimen (e.g. blood, cerebrospinal fluid (CSF) or urine) for the presence
of microorganisms.
Nucleic acid detection: Nucleic acid probes can be designed to detect these
sequences, identifying pathogen-specific nucleic acid in body fluids or
tissue. The use of nucleic acid amplification techniques (NAATs) such as
the polymerase chain reaction (PCR) has increased the power of these
tests to detect very small quantities of microbial material.
• Culture
Culture techniques can be applied to a wide variety of bacteria, fungi
and viruses. Viruses are particularly difficult (and in many cases
impossible) to culture in the laboratory.
• Immunodiagnostic tests
These can be divided into two types:
• tests that detect microbial components, using a polyvalent antiserum or
a monoclonal antibody.
• tests that detect an antibody response to infection (serological tests).

20. Management:
• Many infections, particularly those caused by
viruses, are self-limiting and require no treatment.
• The choice of antibiotic should be governed by:
The clinical state of the patient.
The likely cause of the infection.
• Serious infections may require supportive therapy in
addition to antibiotics.
• Some patients are too unwell to wait for results
(which in the case of culture may take days).
• In diseases such as meningitis or septicaemia delay
in treatment may be fatal and therapy must be
started on an empirical basis.

21. • Special circumstances:
1. Returning travellers.
2. Immunocompromised patients; eg bacteria and
fungi.
3. Injecting drug user; eg Hepatitus virus, Staph.
aureus and group A streptococci and certain fungi.
4. Highly transmissible infections; eg influenza, Lassa
fever, and Ebola.