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