Introduction to Parasites Flashcards
What is a parasite
An organism that lives in another organism (host) and gets its food at the expense of this host
They are simple organisms but more complex than bacteria and consist of a wide range of pathogens
Where can parasites cause infections
Tropics
Subtropics
Temperate climated
What parasitic disease causes the most deaths globally
Malaria
What are the three main groups of parasites
Protozoa
Helminths (worms)
Arthropods
What type of organisms are classified as protozoa
Malaria
Amoebae
Flagellates
What type of organisms are classified as helminths (worms)
Roundworms
Tapeworms
Flukes
What type of organisms are classified as arthropods
Lice
Ticks
Mites
What are protozoa
Microscopic one celled organisms
Can be free-living or parasitic in nature
Can multiply in humans
How can protozoa be transmitted
Fecal-oral route
Arthropod vector
Why type of protozoa use the fecal-oral route transmission
Protozoa that live in a human’s intestine
Why type of protozoa use the arthropod vector transmission
Protozoa that live in the blood or tissue of a human
What are roundworms also known as
Nematodes
What are tapeworms also known as
Cestodes
What are flatworms also known as
Trematodes
How can a definitive diagnosis be made
From the identification of parasites in the host tissue or excreta should be obtained
Using microscopy to identify the different stages (i.e. parasites, cysts and ova) in the faeces
Why should serology be used instead of a culture
Culture is rarely possible
Serology can be useful to detect antibodies (e.g. when parasite is located in deep tissue sites
Give examples of protozoan infections
Malaria
Amoebic Dysentery
Leishmaniasis
What is malaria
A mosquito-borne disease (uses Anopheles mosquito as its vector) caused by a parasite
What do patients with malaria normally experience
Fever
Chills
Flu-like illnesses
If left untreated they may develop severe complications and die
How many types of the plasmodium species are there which can cause malaria
4
Which plasmodium species has the highest mortality rate for malaria
P. falciparum
What types of blood films will be used for malaria
Thick and thin giemsa stained blood films will show the infected red cells
What are parasite infected red blood cells called
Parasitaemia
Describe the life cycle for malaria
Sporozoites are injected under the skin by the mosquito
This travels through the blood and will enter the liver where it matures and re-enters the circulation as merozoites
They invade red cells, multiply and lyse to reinvade more red cells
What happens to the crescent shaped gametocytes produced in the malaria life cycle
They are taken up by the mosquito
How can malaria be prevented
Use of insecticide treated mosquito nets (ITNs)
Prophylaxis
How many cases of amoebic dysentery are there a year
200-400 million cases/yr
100,000 deaths/yr
What is amoebic dysentery
An infection which causes diarrhoea with blood/pus
The trophozoite ingests red cells by removing pseudopodia (‘hot stool’)
When are the symptoms of amoebic dysentery most common
During an infection by Entamoeba histolytica
What can be seen under a microscope in amoebic dysentery
Cysts formed in the stool
What does Entamoeba histolytica cause clinically
Intestinal and extra-intestinal infections
Liver abscess filled with reddish-brown pus in late disease
How many Leishmaniasis species are there
Several
What can the Leishmaniasis species cause
Cutaneous or muco-cutaneous Leishmaniasis
Visceral Leishmaniasis
What can Cutaneous or muco-cutaneous Leishmaniasis cause
Skin or mucosal ulceration
What can visceral Leishmaniasis cause
Fever
Weight loss
Hepato-splenomegaly
What is the Leishmaniasis species infection caused by
Sand-fly bite
How can a Leishmaniasis species infection be diagnonised
Through the histology of biopsied materials
Give examples of nematodes
Enterobiasis
Ascaris lumbricoides
How does enterobiasis present and where is it mainly found
1cm
Threadlike
Found in children
How can enterobiasis be diagnosed
By pressing adhesive sellotape against the perianal region in the morning
By seeing ova under a microscope
How do ascaris lumbricoides work
Through their ingested eggs which hatch in the intestines
The larvae are carried through circulation into the lungs and swallowed again causing adult worms to develop in and inhibit the small intestine
How can ascaris lumbricoides be diagnosed
Ova can be seen in faeces by microscopy
State some features of ascaris lumbricoides
Largest nematode in the human intestine measuring between 15-35 cm in length
Often asymptomatic but can cause transient pulmonary symptoms (Loefller’s syndrome).
Mass of worms can obstruct the small intestine or common bile duct
Where can cestodes be found
Taenia saginata (beef) Taenia solium (pork)
How does cestodes enter taenia saginata (beef) and taenia solium (pork)
Larval cysts are ingested in the meats which act as intermediate hosts
What is the adult tapeworm caused by larval cysts definitive host
Humans
What are tissues cysts in humans infected with T. solium called and how do they occur
Cysticercosis
Through the ingestion of T. solium eggs
How can T. solium be diagnosed
Ova in stools on microscopy
What is the echinococcus species (tapeworms) carried by
Dogs
Wolves
Foxes
How does the echinococcus species enter the human body
Humans ingest eggs through dog faeces
The eggs hatch and enter circulation
A hydatid cyst forms in liver
How must the cyst caused by the echinococcus species be removed
Surgical resection which must remove the whole cyst
What is Trematodes Schistosomiasis and how many species are there
A type of helminths
3 main ones
What are the three main species of Schistosomiasis
S. haematobium (bladder)
S. mansoni (intestinal)
S. japonicum (intestinal)
Where are Schistosomiasis found in high quantities
Fresh water
What is important for the Schistosomiasis life cycle
Snails
Describe the Schistosomiasis life cycle
The Schistosomiasis eggs (ova) are excreted in urine or faeces
Miracidia is released in freash water
They penetrate the body of a snail, which acts as an intermediate host
Cercaria emerge from the snails after 4-6 weeks
They then penetrate human skin causing swimmer’s itch and migrate through the lungs to the liver.
In the liver they mature into worms (schistosomes) which migrate to mesenteric or bladder venules to lay eggs which cause inflammation in the bladder or intestinal wall
What is the most severe kind of schistosomiasis
Schistosoma japonicum
What does schistosoma haematobium cause
Haematuria
Bladder cancer
What is a helminth infection normally accompanied by
Eosinophilia
Elevated IgE
