Parasitology introduction Flashcards
What are the factors that influence the severity ,morbidity and motility caused by parasites
- Pathology id dependent on site and mode of infection ,parasite burden and host immunity
- parasites also have an impact on the economy and social factors ( mostly in tropical areas eg SA , S America and some regions in India
define parasite
A parasite is an organism that lives in or on a host organism and benefits by deriving nutrients from the host
medical parasitology is the study of invertebrate animals capable of causing disease in human and other animals
list 3 types symbiotic relationships
- Mutualism : where both organisms benefits
- Commensalism : Where one organism benefits while the other is not harmed
parasitism : where one organism benefits and the other is not harmed
List the 6 most common Neglected Tropical Disease
- Soil -transmitted helminths ( A lumbricoides , T .trichiura ,hook worms )
- Schistosomiasis
- Lymphatic filariasis
what are neglected tropical diseases
Diverse groups of tropical infections on low income populations in developing countries
caused by pathogens ( viruses,bacteria, parasites
What are the mechanisms of damage of parasites -6
- Mechanical tissue damage
- Direct enzymatic tissue damage
- damage caused by migration or penetration
- depletion of nutrients and blood loss
- secretion of toxins
- host immune response
Types of parasites
- Protozoa (unicellular)
* amoebae(Entameoba)
- Apicomplexa(Cryptosporidium ,Plasmodium)
- Flagellates (Giardia)
- Ciliates(balantidium )
2.Metazoa (multicellular)
*Platyhelminths(flat worms)
+Trematodes(schistosoma)
+Cestodes(Taenia , Echinococcu)
- Nematodes(Ascaris ,Strongyloides)
- Aethropods/Ectoparasites (sarcoptes acabiei )
Parasite life cycles
- Direct life cycle : Transmission from one host to another host of the same species
- Indirect life cycle : life cycle involves to or more hosts of different species
* Definitive host ( sexual reproduction in host)
* Intermediate host(asexual reproduction ,larval stages)
* Accidental host (unable to complete life ccycle ) - Vectors : Carries parasite from one host to another
- Diagnostic host : A developmental stage that can be detected in stool , blood, urine ,sputum, CSF or other body secretions
Discuss the Entamoeba histolyics(protozoa : Ameobae) Epidemiology
- Infection found world wide- frequent in tropical areas
- Due to poor sanitation( faeco-oral)
- In SA ,most common cause of parasitic diarrhea
Discuss the Giadia lamblia/ intestinalis(Protozoa;flagellates) epidemeiology
- found world wide
- 5% of stool contain giardia cysts
- 50% who are infected are asymptomatic carriers who continue to excrete cysts for years
- can cause a outbreak
- Risk groups : children in day care
- In SA ,13 to 17 % prevalence - school children
Cryptosporidium parvum (Acomplexa )
- Worldwide
- resistant to normal water purification procedures eg chlorination and ozone
- High risk group : disease in immunocompromised patients can be severe ,veterinary personnel ,animal handlers and homosexuals
- Can cause outbreaks
- Asymptomatic carriage is possible
- Disease in health humans usually mild ,self limiting disease , disease in immunocompromised patients can be servere
second most common cause of diarrhoea
Blood and TISSUE PROTOZOA(Apicomplexia; Plasmodia species
*Only Plasmodium falciparum ,P.vivax ,P.ovale,Pmalariae can cause malaria
Discuss the epidemiology of malaria
*10% of population is at risk of malaria in SA
Risk region is SA includes low-laying areas of Mpumalanga ,KZN ,Limpopo
Urogenital protozoa (flagellates)
*Trichomonas vaginalis causes trichomoniasis
pathogenesis
*Sexually transmitted
located in vagina and urethra/prostate
*common sexually transmitted infection
Epidemiology
*prevalence of infection approximately 6.5%
discuss the structure and life cycle of Cestodes( metazoa : Platyhelminths )
- Strucure
* flattened , no digestive tract ,simple absorption of nutrients
* scolex(head) with sucker and hooks
* segmented hermaphroditic proglottids
2.life cycles
*Indirect life cycle
-definitive host : sexual reproduction occurs
>Taenia ; human
> Echinococcus : dog
*Intermediate host : harbourrs larval stage (cysticercus)
>Taenia solium -pig
>Taenia saginata -cattle
>Echinococcus granulosus -sheep usually :human dead accidental hosts
Echinococcus granulosus
- Tape worm of digs and other canine spp
- humans are unusual intermediate hosts
- sheeps are the usual intermediate hosts
- after eggs are ingested ,larvae hatch in small interstine and penetrate gut mucosaa and are carried off into the blood stream to other organs
Cestodes : taenia solium life cycle
*Human infections are acquired by eating undercooked beef or pork containing encysted larval stages
*larvae hatches in the small interstine
*When sexually matured ,it produces eggs
the eggs are not laid
*they are passed with faeces
*Animals become infected by by ingesting eggs from contaminated pastures with inadequate treated sewages
T. soliuminfection directly correlated with eating insufficiently cooked pork
Cysticercosis found in areas whereT. soliumis prevalent; directly correlated with human fecal contamination of environment/food/water (poor sanitation/lack of toilets)
T. soliuminfection and cysticercosis found worldwide
Africa - endemic in large parts of sub-Saharan Africa from Senegal in the west to Kenya and Tanzania in the east, and Mozambique and South Africa in the south (Eastern Cape)
When eggs hatch in human host and develop into cysticerci .When thesse forms in the brain ,they may cause neurocysticercosis
T. saginata
T. saginataoccurs worldwide
Humans and cattle perpetuate the life cycle: human feces contaminate water and vegetation with eggs, which are then ingested by cattle
discuss the pathogenesis of Taenia
- Adult taenia atttached to intestinal wall causes little damage
- Can cause mild to non specific signs and symptoms after ingestion of the cysticercia ,abdominal pains ,nausea ,diarrhoeas or constipation might arise and last until tapeworm dies following treatment
Taenia solium cysticerci (larvae) can become very large and migrate to muscle and organs, manifest as space occupying lesion, calcify.
NEUROCYSTICERCOSIS: seizures, hydrocephalus
Living cysticerci do not cause inflammation, but when they die they can release substances that provoke an inflammatory response
E.granulosus pathogenesis
Eggs hatch larvae in gut – migrate in blood to various organs – form large, unilocular cysts. Hydatid cyst is a space-occupying lesion. If cyst ruptures, antigens in the fluid can cause anaphylaxis
Discuss the structural properties of schistosoma speces ( Metazoa: platyhelminthe>tredatodes)
Adult flukes: flattened, leaf-like, sexes of adult flukes separate but male and female live attached to each other
The 3 species can be distinguished by the appearance of their eggs under the microscope
S. mansoni eggs have a prominent lateral spine( found in feces)
S. japonicum eggs have a very small lateral spine ( found in feces)
S. haematobium eggs have a terminal spine (found in urine)
epidemiology of tredatodes
Distribution:
Schistosoma haematobium: Africa, Middle East
Schistosoma mansoni: Africa
Schistosoma japonicum: Far East
S. Africa: S. haematobium, S. mansoni
KZN, Mpumalanga, Northern Province
