Week 24 - protozoan microorganisms Flashcards
Parasites as a health concern
Parasites are studied by a branch called parasitology
Parasitic infections accounted for around 2-4% of Infections and parasitic diseases
(IPD) hospital admissions in the UK only:
-Mostly caused by protozoa
-Higher percentages for other countries
-Health threats for pets
Endoparasites
ENDOparasites
-Inside of the host’s body ->permanently
-Some anaerobes, some aerobes
-CLASSES -> protozoa and helminths
Ectoparasites
ECTOparasites
-On the OUTER surface of the host’s body – temporary or permanent
-Aerobes
-Some ectoparasites serve as vectors of pathogens
-CLASSES -> ticks, fleas, lice, and mites
Endoparasites - protozoa and helminths
Protozoa:
-Monocellular
-Mostly asexual (binary fission)
and sexual reproduction
-Different groups according to
their locomotion modes
Helminths:
-Pluricellular -> parasitic
worms (usually visible)
-Sexual reproduction only
-Move through muscular
contractions
Protozoa general characteristics
-Monocellular eukaryotic cells (2-100 μM)
-All protozoa are chemoheterotrophs -> similar requirements of the mammalian cells
-Diverse oxygen requirements
Either free-living or parasitic with many hosts
-> ~ 20 human pathogens
-> Animal and plant hosts, including pets
Protozoa cell characteristics
Similar intracellular composition to eukaryotic mammalian cells,
with some exceptions:
-Do not contain cell wall, but some contain a pellicle -> a flexible, proteinaceous covering
-Contains vacuoles
-The plasma membrane contains different structure for
movement:
-Pseudopods -> temporary plasma membrane extensions
-Cilia
-Flagella
Life cycle stages
Some protozoa exist in two morphological forms/stages:
Vegetative (Trophozoite):
-Motile, vegetative (active) form
-Actively feed & multiply
-Pathogenic form
Dormant (Cyst):
-External, non-active form
-Protection against stress -> it forms an unusual cell wall
-Non-parasitic form - means of
transfer between hosts
-High resistance against
disinfection and therapeutics
Cyst -> transmission
Vegetative -> pathogenesis
Life cycle stages -> transmission
Transmission of enteric
protozoa (e.g. Giardia) occurs
through a faecal-oral route
-Contaminated food
-Contaminated water
-Domestic pets
-Sewage/waste water
A concern under inadequate
sanitation and poor hygiene practices
Medically relevant protozoa – motility modes
Most protozoan infections can be inapparent/mild, yet life-threatening in
immunosuppressed patients
Protozoa classified by their motility mode:
1. Amoebae - through pseudopods
2. Flagellates - use flagella
3. Ciliates - use cilia
4. Sporozoa - Non motile, spore-producing
->Motility structures can be used to spread other tissues within the body
Amebae
Move by extending pseudopods
-> arm-like projection of the cell membrane
-Engulf food with pseudopods and phagocytize
Flagellates
Possess one or more flagella for
locomotion and sensation
They target different human tracts:
-Intestinal and genito-urinary
-Blood and tissue flagellates
Vectors
Carry and transmit the parasites
Leishmania
Transmission of blood borne protozoa - Leishmania
In humans, Leishmania spp. parasitise in mononuclear phagocytic cells -> macrophages, monocytes
Leishmania species spread through the bite of sand flies (vectors)
Leishmaniasis produces a spectrum of diseases:
Cutaneous leishmaniasis: Affects the skin -> causing skin ulcers
Mucosal leishmaniasis: Affects the mucous membranes of the nose and mouth, causing
sores and destroying tissues
Visceral leishmaniasis: Affects the internal organs, particularly the bone marrow, lymph nodes, liver, and spleen
Ciliates
Protozoa that move by cilia -> hair-like structures that protrude from the surface of cells
-Distributed in rows or patches
Sporozoa
-Do not have any locomotory extensions
-Complex life cycles -> alternating sexual and asexual reproduction, involving spores
-Usually, they have more than one host (human and vector hosts)
Plasmodium spp.
-Agent responsible for malaria – the major and most deadly protozoa-causing disease
-Obligate intracellular parasite – sporozoan
4 species responsible – P. falciparum, P. vivax, P. malariae and P. ovale
->P. falciparum causes the most severe disease and is the most common
Transmission:
-Spread to humans by the bite of female mosquitoes (of the genus Anopheles)
-Blood transfusions
-Mother to foetus
Malaria
-Around 250 million new cases
annually
-600,000 deaths each year
Endemic in tropics –
subtropic countries
-Endemic -> disease present
at a constant level
-Risk for travellers visiting
these areas
Malaria
Symptoms:
-Acute febrile illness -> symptoms start after 10-14
days from mosquito’s bite
-Headache, fever, chills, sweating, dry cough, back pain, muscular fatigue and pain, nausea and vomiting and spleen enlargement
Serious complications may occur
-Cerebral malaria
-Severe anaemia
-Death if untreated / misdiagnosed
Malaria and life cycle of plasmodium
The life cycle of Plasmodium spp. is linked to the malaria transmission modes
-Mosquito bites infected person and becomes infected
-Infected mosquito bites person and person becomes infected
-Infected liver (no symptoms at this stage)
-Infected red blood cells
-Person exhibits symptoms
-Cycle continues
Malaria control measures
2 Vaccines:
-Modest efficacy over time
-Preventing 70-30% of severe cases
Antimalarial preventive drugs:
-Reducing the risk of malaria of 90%
-Before travel into an endemic area until 4 weeks after leaving the area
Personal protection against mosquitoes:
-Insect repellents - 50%
Diethyltoluamide (DEET)
-Covering clothes or nets
Environmental mosquito controls:
-Destruction of mosquito
larvae
Treatment of malaria
Several classes of antimalarial drugs are available
The choice is based on:
-Type of infecting Plasmodium species -> different drug susceptibility
-Clinical status of the patients -> disease severity, comorbidities
-Previous use of antimalarial drugs
-Drug resistance
Antiprotozoal drugs
Antiprotozoal drugs:
-Protozoal diseases are
spreading geographically
-Protozoa are eukaryotes like
human cells -> difficult to treat
-Most mechanisms of action are
not completely elucidated
-Some antiprotozoal drugs
cause serious toxic effects
-Most have not proven to be safe for pregnant patients
Principles of microorganisms identification
