Lecture 3C - Protozoa Flashcards
How can protozoan infections be transmitted?
they can be ingested or transmitted by blood infusion, enter through wounds and be injected by ectoparasite vectors such as mosquitos
What are protozoa?
single cell eukaryotic cells with a membrane bound nucleus, cellular organelles and a surrounding cell membrane
How can protozoa reproduce?
asexually and rapidly to grow in very large numbers
What can protozoal parasites invade?
cells such as red blood cells, so as to hide from the immune system
What to protozoa use the nutrient pathway for?
to fuel their own growth and division
How do protozoa evade the immune system?
they often change their surface coats at a rapid rate so that the immune system is faced with trying to hit a moving target
finding constant regions of surface proteins to target with a vaccine is very challenging
Examples of water borne protozoa?
Giardia lamblia (500x10^6 infections), cryptosporidium, entamoeba histolytica (0.5x10^6), trichomonas
E. histolytica?
amoebic dysentery, also forms abscesses in the brain, liver and lung
can cause ulceration of the gut wall and if this results in gut wall perforation it can be life threatening
Trichomonas?
WB
(180x10^6)
infects the urogenital tract, causes vaginitis in women
What do water borne protozoa cause?
they infect the gut and cause severe diarrhoea and bloody stools
What are common vectors for protozoal infections?
insects
What are protozoal infections a major cause of?
disability, illness and death
Trypanosoma?
INSECT BORNE
causes sleeping sickness (T.brucei gambiense, Africa)
extracellular in blood first, then CNS or heart depending on species
Leishmania?
INSECT BORNE
sand fly
intracellular macrophages
skin sores, swelling of liver and spleen, low white cell count (lysis), can be fatal
Toxoplasmosis?
INSECT BORNE
cat faeces are a major source of infection
widespread infection in humans
can cause foetal damage and some suspected linkage to schizophrenia
Plasmodium?
INSECT BORNE
cause of malaria, intracellular
causes fever and can be fatal
How many cases of malaria were there worldwide in 2017?
219x10^6
What are insect borne protozoa?
the insect is the vector of the disease and injects the protozoan when it comes in for a blood meal
What can ticks transmit?
lyme disease, typhus, encephalitis
need to be removed with tweezers
What can fleas transmit?
typhus and plague
What can sandfly transmit?
leishmania
What can the tsetse fly transmit?
sleeping sickness
What can the reduvid bug transmit?
chagas disease
What can the simulum fly transmit?
onchocerciasis
What % of insects were found to be infected with malarial parasites?
5%
from one study
What precautions should be taken in a malarious area?
bed nets, long sleeved clothing and covering legs, insect repellants, avoiding situations where biting is more likely
What else can mosquitos transmit?
dengue, yellow fever, chikungunya, elephantiasis
What is malaria?
a potentially fatal protozoal infection, carried by mosquitoes
Untreated malaria results in?
cyclic fever, chills
the destruction of red blood cells and sometimes the blockage of cerebral blood vessels
some forms can be fatal
Where is 90% of the malaria disease burden?
in the tropics
What can affect the malarial disease range?
travel, military activity and the greenhouse effect
How many people are at risk of malaria?
2-2.5 billion (40% of world population in 100 countries)
How many cases of acute malaria are there annually?
300,000,000
How many deaths does malaria cause annually?
1.5-3 million
In Africa, what does malaria cause?
1/4 of all deaths in children under 5, this makes up 1/3 of all hospital admissions
How many malarial deaths are in children?
70% of the deaths
this is because they have a small blood volume and cannot cope with large infections of RBCs
they also have immature immune systems
How are malarial sporozoites injected?
from the salivary gland of the female mosquito into the human tissue when it bites into the skin for a blood meal
Why do male mosquitos not transmit malaria?
they are vegetarian
Where are the two main phases of the plasmodium life cycle?
one in humans and the other in insects
When the mosquito bites, where do the injected sporozoites go?
rapidly make their way to the liver
What do sporozoites occupy?
a sinusoid of the liver and there they rapidly multiply
What other form can sporozoites take in the liver?
they may enter a dormant, hypnozoite phase which can erupt months later
depends on the species
What happens when the sporozoite has multiplied up to 1000 fold in the liver?
the infected liver bursts and the merozoite form is released into the bloodstream
In the blood stream, where does the merozoite form go?
into red blood cells where they can mature, multiply and eventually burst the red blood cell
What happens when the infected red blood cell bursts?
it releases more infectious merozoites and fever stimulating granules of digested haemoglobin
What are signs of malaria?
fever and anaemia
anaemia due to loss of red blood cells
What is plasmodium falciparum
the most common and most dangerous form of malaria as it can cause cerebral malaria
Life cycle of plasmodium falciparum?
appears in blood 5.5 days after initial infection
has a 48 hour life cycle and malignant tertian (3 days) appearance of fever and can be fatal
How long can blood donors be infective with plasmodium falciparum?
5 years
What plasmodium species do NOT have a hyponozoite (dormant) phase?
plasmodium falciparum and plasmodium malariae
Plasmodium malariae?
emerges into the blood 15 days after infection
72 hour cycle benign quartan fever (erupting every 4 days)
less common
blood donors may be infective for years
Plasmodium ovale?
widespread species, benign tertian malaria
blood donors infective for 7 years
Plasmodium vivax?
more rare
benign tertian form of malaria
blood donors infective for 5 years
What plasmodium species HAVE a hypnozoite stage?
plasmodium ovale and plasmodium vivax
Plasmodium knowlesi?
has a localised prevalence in some parts of south east asia
