Parasitology and Pathogenesis of Parasite Infections Flashcards
What is a parasite
A parasite is an organism that lives on or in a host organism and gets its food from or at the expense of its host.
What are the three main classes of parasites that cause disease in humans
- Protozoa
- Helminths
- Ectoparasites
What are protazoa
- Protozoa are microscopic, single-celled, free-living or parasitic organisms.
- They are able to multiply in humans allowing serious infections to develop from a single organism.
How are protozoa trasmitted
- Protozoa living in the human intestine can be transmitted by the fecal-oral
route
-Protozoa living in blood or tissues are transmitted by an arthropod vector
How are protozoa classified
They are classified by they mode of movement
What are the different groups of protozoa
- Amoeba, e.g. Entamoeba
- Flagellates, e.g. Giardia, Leishmania
- Ciliates e.g. Balantidium
- Sporozoa – organisms whose adult stage is not motile e.g. Plasmodium, Cryptosporidium
Name some medically important protozoa infections
- Entamoeba histolytica
- Giardia lamblia
- Trichomonas vaginalis
- Malaria (Plasmodium spp.)
- Toxoplasma gondii
- Cryptosporidium
- Leishmania spp.
- Trypansoma cruzi
- Trypansoma brucei (gambiense/rhodesiense)
What are helminths
Helminths are large, multicellular organisms (worms) generally visible
to the naked eye in their adult stages. In their adult form, helminths cannot multiply in humans.
What are the main groups of helminths
- Nematodes (roundworms)
- Trematodes (flukes)
- Cestodes (tapeworms)
List some medically important helminths - nematodes
Soil-transmitted helminths:
- Ascaris lumbricoides
- Trichuris trichiura
- Hookworm spp.
- Enterobius vermicularis
Filarial parasites:
- Wuchereria bancrofti
- Loa loa
- Onchocerca volvulus
- Dracunculus medinensis
Others:
- Toxocara canis/cati
- Trichinella spiralis
List some medically important helminths - Trematodes
- Schistosoma mansoni/haematobium/jap nicum
- Clonorchis sinensis
- Fasciola hepatica
- Paragonimus spp.
List some medically important helminths - cestodes
- Taenia saginata
- Taenia solium
- Echinococcus granulosus
What are ectoparasites
Blood-sucking arthropods such as ticks, fleas, lice, and mites that attach or burrow into the skin and remain there for relatively long periods of time (e.g., weeks to months).
List some medically important ectoparasites
Mites:
- Scabies
- Trombiculid
Ticks:
- Hard
- Soft
Lice:
- Pediculus humanus capitis
- Pediculus humanus humanus
- Pthirus pubis
Flies:
- Botflies
Where are causes of high incidence rates of parasite infections
- Tropic and subtropic climates
- Temperate climates
- In rural areas of low-income countries
- High migration
What types of hosts can parasites have in their life cycle
- Intermediate – host in which larval or asexual stages develop
- Definitive – host in which adult or sexual stage occurs
What are the type of vector parasites can have
- Mechanical when no development of parasite in vector
- Biological when some stages of life cycle occur
What are the determinants of parasite infections
- Depends on mode of transmission and opportunities for transmission
- Faeco-oral
- Food
- Complex life cycles
- Others
What are the Faeco-oral determinants of parasite infections
- Household sanitation
- Access to clean water
- Personal hygiene behaviours
What are the food related determinants of parasite infections
- Animal husbandry
- Surveillance
- Regulations and government controls
How can complex life cycles be a determinant of parasite infections
There are distributions of vectors and intermediate/definitive hosts
What are the other determinants of parasite infections
- Government resources and level of human development/per capita income
- Education
- Country-level and regional control programmes
- Availability of cheap and efficacious treatments
- Construction and building regulations (eg Chagas)
- Urban vs. rural residence
- Environmental sanitation
Describe the life cycle of Trypansoma cruzi
- Triatomine bug takes a blood meal
- Metacyclic trypomastigotes penetrate various cells at the bite wound site. Transform not amastigotes inside cells
- Multiply by binary fission in infected tissue cells
- Transform into trypomastigotes then burst out into the bloodstream
- Triatomine bug takes a blood meal and trypomastigotes ingested
- Epimastogtes in midgut multiply and become metacyclic trypomastigotes in hind gut
What are the three phases of the Chagas disease
- Acute
- Chronic ‘indeterminate’
- ‘Determinate’ Chronic disease
Describe the onset of the acute phase of Chagas
- Incubation 1-2 weeks after bite
– Up to months after transfusion
– Trypanosomes in blood
Describe the symptoms in acute chagas
Occurs within 3 weeks
Generally mild or asymptomatic:
- Local swelling (Romaña)
- Nodule or chagoma
- Fever
- Anorexia
- Lymphadenopathy
1-2% diagnosed
Symptoms last 8-10 wks
Rarely (young and IS):
- Hepatopsplenomegaly
- Acute myocarditis
- Meningoencephalitis
- Fatality <5% of
symptomatic
Describe the Chronic ‘intermediate’ phase of chagas
- Lifelong infection
- Generally trypanosomes not detectable but often positive for parasite DNA
- Seropositive
- 60-70%
- Normal ECG and X-rays
- Cardiomyopathy/Heart failure
Describe the ‘Determinate’ Chronic disease phase of Chagas
- Seropositive
- 30-40% of infected 10-30 years after infection
- 5-10% develop chronic Chagas immediately after acute disease
What is the digestive effect of chronic chagas
- Develops in 10-15% of patients with chronic infections
- Esophagus, rectum, and sigmoid colon are most affected
- Patients present with constipation
- Complications seen as: Faecaloma, Obstruction, Sigmoid volvulus, Ulceration, Perforation
Describe the pathogenesis in acute chagas
- Tissue damage caused by inflammatory response to parasites in nests of
amastigotes in cardiac, skeletal, and smooth muscle - Parasite killing by antibodies, activated innate immune response and Th1 pro- inflammatory cytokines.
Describe the pathogenesis in intermediate chagas
Regulatory immune response characterized by IL-10 and IL-17
Describe The pathogenesis in chronic chagas
- Chronic inflammatory response to persistent parasites in muscle and nerve cells
- Autoimmune mechanisms
- May vary by parasite strain and tissue tropism
- Predominance of Th1 cytokines and CD8+ T cells
Describe the existence of the Leishmaniasis disease across the world
Visceral leishmaniasis:
- Asia - Leishmania donovani
- Middle East/Africa/Asia - L. infantum variants
- Latin America - L. chagasi
Cutaneous leishmaniasis:
- Mediterranean/Middle East - L. Infantum/L. major/L. tropica
- Central and South America - L. braziliensis/amazonensis/mexicana
Describe the life cycle of Leishmaniasis
- Sand fly bites skin
- Promastogote enters and is engulfed by histiocyte
- Multiply by binary fission in cell
- Amastigotes released from histiocytes and can infect other cells
- When sand-fly bites again it takes up amastigotes
What is the vector for leishmaniasis
Lutzomyia/Phlebotomus
Sand-fly
Bites at night and is small enough to fit though mosquito nets
what can act as reservoirs for leishmaniasis
- Domestic animals
- Sylvatic animals
What forms can cutaneous leishmaniasis show up as
- Small papule
- Plaques
- Ulcers
Diagnosed by scarping ulcer and analysing with microscope
Describe the effect of diffuse cutaneous leishmaniasis
Occurs when individuals cannot mount an immune response against the parasite
Highly pappilated
Describe the symptoms faced in mucocutaneous leishmaniasis
- Destruction of soft tissue in nose and facial regions.
What is the pathogenesis in acute lesions of cutaneous leishmaniasis
- Tissue damage caused by inflammatory response to presence of parasites in
macrophages - Parasite killing by Th1 pro-inflammatory responses and macrophage killing.
What is the pathogenesis in latent cutaneous leishmaniasis
Parasites remain present long-term. Regulatory immune response characterized by balance of Th1 and anti-inflammatory responses
What is the pathogenesis in relapse of cutaneous leishmaniasis?
Alteration in immune response (i.e change in Th1 vs. immune regulation secondary to HIV, malnutrition) may trigger relapse:
- Mucocutaneous disease associated with strong but inadequate inflammatory response to
parasites that have metastasized to mucosa - Diffuse cutaneous leishmaniasis associated with uncontrolled parasite replication
- Recividans – recurrence of lesions at old ulcer site.
What are the three main species involved in schistosmiasis
- Schistosoma mansoni
- S. haematobium
- S. japonicum
Describe the life cycle of schistosomiasis
- Miracidia enters snails and undergo cycle
- Cercaria emerges from snails
- Enter host by penetrating skin or mucous membranes
- Migrate via the heart to the portal vein
- Schistosmula develops into male and female adult worms in portal and mesenteric veins
- Worms copulate and move to vesicle veins, eggs are deposited and extruded through bladder mucosa
- Eggs are passed in urine
- Eggs hatch and release mircidia in water
Describe the presentation of cercarial dermatitis due to schistosomiasis
- Exposure to cercariae from
animal or bird schistosomes - Requires pre-sensitization
- Allergic-type reaction
What are the key features of immune response in granuloma formation
- Eggs become organized in granulomas
- Repeated insults and tissue repair leads to fibrosis and
organ damage - Cirrhosis - Damage of the liver by the eggs
Describe Hepato-intestinal schistosomiasis
Infections with
S.mansoni and S.
japonicum
Pathology caused by
immune response to
eggs
Causes hepatospenomagaly
Describe Urinary schistosomiasis
Damage to bladder by granulomas and damage to epithelial layer when eggs are pushed through
Blood present in the kidney - Haematuria
Higher risk of carcinoma of baldder
What is Onchocerciasis
- Major blinding disease
- Caused by filarial parasite ( Onchocerca
volvulus) - Transmitted by blackflies
- Causes river blindness
Describe the lifecycle of onchocera volvulus
- Black fly takes a blood meal, L3 larvae enter at bite wound
- Grows into adults in subcutaneous tissue
- Adults produce unsheathed microfilarie that is found in skin but also in urine and sputum
- Black fly takes a blow mean and ingests microfilarie
- They penetrate blackly’s midgut and migrate to thoracic muscles
- Become L1 Larvae
- Become L3 larvae
- Migrate to head and blackly’s proboscis
what is the vector for onchocerca
The simulium, a species of fly
Describe the pathology of onchocerciasis
Repeated episodes of inflammation to presence of microfilariae leads to permanent damage and scarring in skin and eyes
How does microfilariae present in patient
- Presents as little bumps on the skin
- An inflammatory response to microfilariae in the skin
How is onchocerciasis a clinical disease
Onchocercal nodules
Skin disease:
- Acute papular onchodermatitis
- Chronic onchodermatitis
- sowda
Eye disease:
Anterior segment:
- Punctate keratitis
- Acute iridocyclitis
- Sclerosing keratitis
Posterior segment:
- Optic neuritis/atrophy
- Chorioretinopathy
What is acute papular onchodermatitis
Bumps on the skin as an immune response to nodules
How does chronic onchodermatitis present
- Present as elephants skin symptoms
- Chronic inflammatory response
How does punctate keratitis present
damage to the eye
How does sclerosis keratitis present
Occlusion of the cornea
how does chorioretinopathy present
retina damage
How does optic atrophy present
Damage to optic nerve
What diseases are transmitted via hard ticks
- Tick typhus
- Viral Encephalitis
- Viral fevers
- viral hemorrhagic fevers
- Tularemia
- Tick paralysis
- Human babesiosis
What diseases are transmitted by soft ticks
- Q fever
- Relapsing fever
why are ticks medically important
- Mechanical injury by the bite
- Tick paralysis
- Tick’s toxins produce a block in motor nerve fibres
- Ticks are carriers of many diseases
What are head lice
- Suck blood from the scalp and lay eggs in the hair
- easily spread with contact and sharing of combs
What are body lice
- Sucks blood from the body and lays eggs on clothing
- Spread by bodily contact, sharing of clothing and bedding
- Vectors for diseases such as epidemic typhus, trench fever and relapsing fever
What are crab lice
- Broad,flat lice that appear crab-like
- Mid and hind legs are stout with very large claws
- Abdominal segments have distinct lateral lobes
- Pthirus pubs confined to human pubic region
What drugs are used to control Protozoa
- Tinidazole
- Metronidazole
- Nitazoxanide
- Benznidazole
- Heavy Metals
What drugs are used to control Helminths
- Albendazole/mebendazole
- Praziquantel
- Ivermectin
- Diethylcarbamazine
- Pyrantel
What drugs are used to control Ectoparasites
- Ivermectin
- Benzyl/malathion Lotions
What behavioural changes can control parasite infection
- Education
- Hand washing and hygiene behaviour
What environmental interventions can control parasite infections
- Spraying of residual insecticides for household vectors
- Mosquito nets for malaria
- Improved housing
- Sewage disposal and potable water
- Drainage of swamps
How else can parasite infections be controlled
For many parasite infections in an endemic settings, treatment must
be given periodically or periodically over long periods of time because
re-infections are rapid or because the treatment kills larval rather
than adult stages
