Infection and DiseaseFungi
ParasitesNosocomial infection
Diagnosis of infectious disease
Fungi
Fungi
• Eukaryotes – nucleus / several organelles
• Non-motile
• Aerobic
• Cell wall made of Chitin
Need for special antibiotics (antifungals):
Fungal diseases –superficial infections
• Superficial infection– ability to infect intact skin /nail
• Caused by dermatophytes
• These fungi use keratin for their growth
• Eg. Trychophyton spp
Fungal diseases –Systemic infections
• Systemic infections:
• Lung infections in healthy individuals
• Not common Eg. Histoplasma spp
Fungi opportunistic infection
• Infection in immunocompromised individuals
• Eg. Aspergillus spp. and Candida spp. in AIDS patients
• Can affect any organ
Fungal toxins
• 1960s – “Turkey X disease” – Brazilian peanut feed
• Linked to fungal toxin from Aspergillus spp. (Aflatoxin)
• Can affect liver, kidney , heart and brain in humans
Parasites• Unicellular (Protozoa) – eg.
Amoebae
• Multicellular worms (Helminths) eg. Round worms /flatworms
• Many parasites require – 2 hosts to complete their life cycle (eg. Plasmodium falciparum)
• Some parasites require vectors for transmission(eg. Mosquitoes)
Entamoeba spp
Round worms
Protozoa
• Eg. Entamoeba spp. – amoeba that can cause dysentery / bloody diarrhoea
• Plasmodium falciparum – causes malaria
Helminths
Nematodes
• Unsegmented worms
• Roundworms
Platyhelminthes
• Segmented worms
• Flat worms
Roundworm (Ascaris spp.) - life cycle
< 100µm
500µm
40 cms
Abdominal painDiarrhoea
Tapeworm (Taenia spp. ) – life cycle
< 50µm
5mm
Up to 10 meters
Indigestion, loss of appetite, abdominal pain
Nosocomial infections or hospital acquired infections
Nosocomial or hospital acquired infections infections
Hospital acquired infections: new infections acquired in the hospital or immediately after discharge
Example of nosocomial infections
MRSA – Methicillin Resistant Staphylococcus aureus ; highly antibiotic resistant
Diagnosis of infectious diseases
Methods in Diagnosis of infectious diseases
Direct methods:• used to detect the microbe
or its components
Indirect methods: • used to detect antibody
response in the host to a microbe
• Direct methods - Microscopy - Culture - Antigen detection - Detection of genomes
• Indirect methods - Serology (Ab detection)
Choosing the right sample
• Choosing the appropriate sample is critical
Factors:• Type of illness• Time from appearance of
symptoms
Typhoid feverWeek 1-2 – bloodWeek 3 - StoolWeek 4 - Urine
Window period
• Period between infection and the point when the lab test can identify infection
• Varies with the test used. (Shorter for direct tests than indirect tests)
Choosing the right test
Dengue• 1-6 days – NS1 antigen
• 5-15 days – IgM Ab against dengue virus
Direct methods
(1) Microscopy
• Light microscopy used for visualization of bacteria, fungi, parasites
• Staining – enhances contrast
• Good for rapid presumptive Dx
Bacteria - unstained
Bacteria stained
Microscopy
• Quick, easy, inexpensive
• Good for microbes that are difficult to grow – MTB, malarial parasite
• Viruses – require electron microscopy
Bacteria in urine
MTB in sputum
Malarial parasite in blood
(2) Culture• Good when the number of microbes in
the sample is low
• Culture media -used for bacteria and fungi
• Human cell lines – used for some viruses
• Time – 2 days to 8 weeks
• Expensive
• Subsequent tests are required for specific identification
Bacteria
Poliovirus in human cells
Fungi
(3) Antigen detection of microbial antigens
• Detection of microbial proteins (antigens) allows specific identification of microbe
• Easy, inexpensive and reliable methods available
Antigen detection: Immunofluorescence
Specific Ab tagged with a fluorochromeRequires fluorescence microscope
Antigen detection: ELISA
Anti-Target Antibody
Enzyme linked immunosorbent assay = ELISA
ELISA Principle
Anti-Target Antibody
Target Protein
ELISA Principle
Anti-Target Antibody
Target Protein
Antibody-Enzyme
Conjugate
Anti-Target Antibody
Target Protein
Antibody-Enzyme
Conjugate
Substrate
ELISA Principle
ELISA-Antigen detection video
https://www.youtube.com/watch?v=70TPrfL_8-M
(4)Detection of microbial genomes
Agarose gel electrophoresis
Applications of PCR
• Highly sensitive (1-10 copies are picked up)
• Early Dx
• Can quantitate microbes - virus loads / response to treatment
• Works on non-cultivable microbes
Indirect methods
(1)Detection of antibodies produced against microbes
Ab detection ELISA Eg. HIV Ab detection ELISA
Ab in sample
Point-of-care tests
Point-of-care tests
• Tests performed at the point-of-care (eg. doctor’s office)
• Can be performed outside a laboratory
• Does not require special training
Point-of-care tests for Ag and Ab detection
• Principle –similar to ELISA
• Rapid (< 10 minutes)
• Available for many infectious agents (eg. HIV, rotavirus..)
Antigen Antibody