Lecture 22 - Parasites And Infections Flashcards
What is a general definition of parasite?
Any living form which is dependent on other living forms for survival, and causing some damage to the host
What are parasites used to describe?
Protozoa Helminths (worms)
What are 3 main types of parasites?
Protozoa
Helminths
Ectoparasites
What is a Protozoa?
Endoparasites (live inside the host body)
What is helminths (worms)?
Ascaris
Taenia
Hookworm
What is ectoparasites?
Live on the surface of the host
Fleas
Lice
Ticks
What are Protozoa?
Not easily defined as very diverse
Distantly related to each other
Belong to kingdom: Protista
All are unicellular eukaryotic organism
Habitats: all aqueous environment (incl soil and us)
Around 20.000 species described (most do not cause disease)
Where are Protozoa diseases common in?
Developing countries
Growing emerging threats in developed countries
What can Protozoa be classified by?
Their means of locomotion
Pseudopodia (Entamoeba histolytica)
Flagella (Trypanosoma)
Cilia (paramecium)
How does Protozoa reproduce asexually?
Binary fission: one cell splits into two
What is schizogony (schizont stage)?
Nucleus divides many times before cell divides
The single cell separates into daughter cells
How does some Protozoa reproduce sexually?
Fusion of gametes (e.g. plasmodium)
What do some Protozoa produce?
Cysts (Giardia, Entamoeba)
Protective capsule to resist unfavourable condition (ie:outside host)
What is Trophozoites?
Protozoa in feeding and growing stage
What are 3 forms of Protozoa disease?
Apicomplexa (SPOROZOA)
Amoebae
Archaezoa - Euglenozoa (FLAGELLATES)
What are examples of Apicomplexa?
Plasmodium species (malaria) Toxoplasma Gondi (toxoplasmosis) Cryptosporidium (diarrhoea)
What is an example of Amoebae?
Entamoeba histolytica (amoebic dysentery)
What are some examples of Archaezoa?
Giardia (diarrhoea, malabsorption)
Trypanosoma (sleeping sickness, Chagas)
Leishmania (Leishmaniasis)
Where are malaria found?
Endemic in parts of Asia, Africa, Latin America and Oceania
How much percentage of the world’s population live in areas where malaria is transmitted?
40%
What does WHO estimate?
212 million clinical cases per year
429,000 deaths in 2015 (sub-Saharan African - under 5 year old children)
50% reduction since 2000
What is malaria caused by?
Apicomplexa protozoan parasites belonging to the genus plasmodium
What are Apicomplexan parasites?
Non-motile
Obligate intracellular parasites
Characterised by complex set of organelles at tip of cell
What are 4 plasmodium species that cause malaria?
Plasmodium falciparum
Plasmodium vivax
Plasmodium malariae
Plasmodium ovale
What plasmodium species is most common?
P. Vivax
80% of malaria infections
What plasmodium species is clinically most important?
P.falciparum
15% of malaria infections
90% deaths
What is the transmission of malaria?
Causative agent is transmitted in the saliva of pregnant female mosquitoes (Anopheles)
30-40 different Anopheles species transmit the pathogen
Anopheles Gambiae is best known as it transmits most common type of malaria
Sporozoites
Found in mosquito saliva gland
Stage transmitted by mosquitos
After injection into the skin, sporozoites move through the dermis until they contact blood vessels
Sporozoites move into the circulatory system
Travel to the liver (30 min after bite)-infect hepatocytes
What does sporozoite develop into?
Liver schizont
What is a schizont?
Multinucleated parasite (asynchronous division of parasite nucleus)
What does the schizont differentiate to form?
Many mononucleared merozoites
Merozoites
Liver cell ruptures
Merozoites released into the bloodstream
Infect red blood cells (RBC)
What does merozoites differentiate into?
Trophozoite stage
What are young trophozoites called and why?
Ring stage
Because of Giemsa staining pattern
Asexual cycle of malaria: RBC
The merozoite changes forming a large mononucleated trophozoite
The trophozoite nucleus divides forming a schizont
The schizont differentiates to generate many uninucleated merozoites
RBC ruptures releasing merozoites into the blood
The merozoite invade new RBC - start new asexual cycle
What does some merozoite upon invading RBC develop into?
Gametocytes
What are RBC containing gametocytes taken up by?
Mosquito
Where does the RBC break down?
Insect gut
What does gametocytes form?
Male and female gametes
What does the gametes fuse to form?
Zygote
What does zygote undergo?
Meiosis in the insect guy wall forming an oocyst
What occurs in the oocyst?
Repeated mitotic division
Producing thousands of sporozoites
When the oocyst ruptures what does it release?
Sporozoites into the haemolymph
Where does the sporozoite migrate?
From gut lining to the salivary gland, starting the life cycle again
What is mosquito?
Primary or definitive host
Host where parasite reaches maturity and sexually reproduces
What are mammals?
Intermediate host
Used to get from insect to insect
What are the pathology and clinical manifestation of malaria due to?
Asexual red blood cell stage
What does the symptoms of malaria depend on?
Cycle of parasite
Immune state
General health
Nutritional status
What are other symptoms of malaria?
High fever Periodic fever every 48 to 72hr Chills Headaches Joint pain Vomiting Weakeness Reveal failure Confusion Seizures
What does cerebral malaria result in?
Tissue death in the brain (P.falciparium)
What is malaria diagnosis?
Microscopic detection of parasite in blood smear
Thick blood film - detection
Thin blood film - species identification
What are the treatment of malaria?
Various antimalarial medications
(Chloroquine, quinine, artemisin)
Type depends on severity of case
What are the prevention of malaria?
Reduce: Human-mosquito context Vector density Parasite reservoir Avoid getting bitten Use anti-malaria medication (chemoprophulaxis) - chloroquine, mefloquine, primaquine Insecticide spray Bed nest with insecticide
How many Leishmania species are there?
More than 20
What are examples of Leishmania?
L. Donovani
L. Major
Where are Leishmaniasis?
Present throughout tropics and subtropics
South-central America, Asia, Africa
How many are infected with Leishmaniasis?
Around 12 millions
2 millions new case per year
50.000 death per year
What is the vector for Leishmania?
sand fly
Female: Phlebotomus, Lutzomyia
What is the pathology of Leishmaniasis?
Begnin skin lesions to fatal systemic disease
What are 3 main diseases of Leishmaniasis?
Cutaneous
Mucocutaneous
Visceral
What is cutaneous?
Form presents with skin ulcers
Self-limiting infection
What is mucocutaneous?
Form presents with ulcers of the skin, mouth and nose
What is visceral?
Form starts with skin ulcers
Later presents with fever, low red blood cells, large spleen and liver
What are the two main parasites form of Leishmaniasis?
Promastigote
Amastigote
What is Promastigote?
Flagellar stage Occurs in sand fly Spindle shape Non-infectious: insect gut, divide by binary fission at 27 Infectious: attach/invade Neutrophils/ macrophages Non-dividing
What is Amastigote?
Aflagellar stage Occurs in vertebrate host Round shape: non-motile Infectious: invade macrophages Divide by binary fission (+500 per single cell)
What is the first stage in life cycle of Leishmaniasis?
Sand fly takes a blood meal in infected host
Ingests macrophages infected with Amastigote
What is the 2nd stage of Leishmaniasis?
Macrophage ruptures releasing amastigotes in insect gut
What is the 3rd stage in life cycle of Leishmaniasis?
In midgut amastigotes transform into non-infectious promastigotes
What is 5-6th stage in life cycle of a Leishmaniasis?
Promastigotes multiply and move to anterior midgut and attach to gut epithelium - prevent elimination
What is the 7th stage of Leishmaniasis?
Some promastigotes form infective metacyclic promastigotes that detach from gut wall
What is the 8-9th stage in life cycle of Leishmaniasis?
Infected sand fly takes a blood meal
Metacyclic promastigotes regurgitated into victims bloodstream
What is 10-13th stage in life cycle with Leishmaniasis?
Promastigote transformed into amastigotes in macrophages
What is 14th stage in life cycle of Leishmaniasis?
Amastigotes multiply in parasitophorous vacuole
What is 15th stage in life cycle of Leishmaniasis?
Vacuole and macrophage lyse and release Amastigote and can be taken up by other macrophages
What does Leishmania recruit and prevent?
Recruit complement
Prevent lytic action
Use complement for phagocytosis
What does Leishmaniasis produce?
Surface molecule lipophosphoglycan (LPG)
Once phagocytosed via complement receptor, what are parasite able to resist?
Acidification
Action of hydrolytic enzymes
Reactive oxygen species in phagolysosome
What is the pathology of cutaneous (Leishmaniasis)?
Most common (10 million case)
Starts as raised painless red lesion at site of sand fly bite
Ulcer wet or dry - no pus formation
Ulcer self heal or diffuse lesion develop
What is pathology of Mucocutaneous?
Metastasises mucocutaneous lesions
(Mouth/nose/soft plate or anus/genitals)
Can appear week to years after infection
Tissue destroyed - can lead to disfigurement
What is pathology of visceral?
Most serious form
High fatality rate - 30.000 death per year
Generalised infection of reticuloendothelial system
Liver, spleen, bone marrow, lymph node:
Protuberant abdomen classical sign
Disease progresss to malaise, weakness, wasting syndrome, death
What is diagnosis of Leishmaniasis?
Detection of parasites in clinical specimen
Detecting amastigotes or culturing promastigotes form aspirates or biopsies from lesions
Serology or intradermal skin tests also used:
Detect anti-Leishmania antibodies ( I.e. K39 Amastigote Antigen)
What is the treatment of Leishmaniasis?
Pentavalent antinomials
Pentamidine
Amphotericin B
What is Pentavelent antimonials?
First line treatment
60 year old drug still, effective - mode of action unclear - inhibit enzymes
Administration: parenteral and long duration treatment
Toxic side effects
Increase in drug resistance in Leishmaniasis
What is Pentamidine?
Interacts with DNA
Inhibits DNA topoisomerase II
What is Amphotericin B?
Alternative to antimonials Damage parasite membrane Administration similar to antimonial Toxicity reduced Treatment expensive
What is the control of Leishmaniasis?
Reduced exposure to sand fly Use of protective clothing Insects repellents Bed nets Insecticide spray
What is the control of reservoir species of Leishmaniasis?
Dogs
Vaccine development
What is Giardiasis caused by?
Giardia duedonalis (lamblia)
What is Giardia duedonalis?
Anaerobic
Flagellated
Eukaryotic protozoan
What is gastrointestinal infection?
Abdominal cramp
Vomiting
Explosive
Watery diarrhoea
What is transmission of Giardiasis?
Faecal/oral (also anthroponotic + zoonotic) could I’m intestinal tracts of animals and in the environment
What does Giardiasis?
Ingests cysts in contaminated water or swimming
Parasite multiply in the gut
What is prevention of Giardiasis?
Filtered water
What is self-limiting infection of Giardiasis?
Asymptomatic to diarrhoea
What is worldwide distribution of Giardiasis?
High incidence (20-30%) in developing countries Developed countries: travellers and institutionalised population
How many people infected with Giardiasis?
200 million people infected
Where does Giardia mature and multiply?
Gut
Where is infective cysts passed in?
Stool
What is the pathogenesis of Giardiasis?
Trophozoites multiply in the jejunum by binary fission
Adhere strongly to intestinal epithelium via sucking disks
Diarrhoea May be due to direct cytotoxicity, apoptosis, disruption of epithelial permeability
Giardia cysts excreted in faeces and able to survive in environment until new host infection
What is Giardiasis infection characterised by?
Diarrhoea Anorexia Abdominal pain Cramps Weight loss Offensive fatty stools
What is diagnosis for Giardiasis?
Microscopic obervation:
Detection of cysts in stools
Aspiration of intestinal content observed for presence of motile trophozoites
What is treatment of Giardiasis?
Metrodinazole main drug
Active against Giardia trophozoites
