L16 & 17 Infection PART 1 Flashcards
Order these organisms from smallest to largest and give examples:
Fungi Prion Insect Virus Protozoa Helminth Bacteria
Prion – Kuru Virus – influenza Bacteria – staphylococci Fungi – candida Protozoa – malaria Insect – fleas Helminths – tapeworm
What is a parasite?
An organism which depends on another for its survival to the detriment of its host
What is an endoparasite?
Lives inside body and major cause of illness eg helminths (worms) and protozoa
What is an ectoparasite?
Lives outside body and cause of minor symptoms but can cause other infections eg fleas, lice, bed bugs and ticks
What is a protozoa?
Unicellular organism – some have complex lifecycles involving more than 1 host
What is an amoebae?
type of protozoa (eg Entamoeba histolytica)
Invades large bowel lining and causes dysentery (abdominal cramps/bloody diarrhoea), is excreted with faeces and spread via contaminated food/water. Poor hygiene/sanitation is a risk
What is a sporozoan?
Protozoa (eg Plasmodium falciparum (malaria))
Lifecycle in both humans and mosquitos, infects RBCs and liver. Symptoms include fever, headache, joint pains and complications include kidney failure, coma and death. Geographical risk.
What is the lifecycle of malaria?
Mosquito bites human, releasing sporozites into blood. In the liver turns into merozoite. In the blood stages through trophozoite, schizont and back into merozoite or gaetocyte. Gametozyte forms into stages of mosquito eg anopheles spp.
What are helminths?
Worms. Complex organisms but Some have complex life cycles with more than one host
Other species have their own helminths which can accidentally cause human disease
Name 3 types of helminths and their structures
Cestodes (tapeworm) – segmented, flat
Trematodes (fluke) – unsegmented, flat
Nematodes (round) – cylindrical, have digestive tract with lips, teeth and anus
What are tapeworms?
Helminth (eg taenia saginata (beef tapeworm))
Intestinal human parasite – largely asymptomatic but can cause abdominal pain and malnutrition. Cattle are intermediate hosts. Diagnosis made by patient and stool microscopy for eggs
What is the life cycle of a tapeworm?
- Eggs or gravid proglottids in faeces and passed into environment
- Cattle and pigs become infected by ingesting vegetation contaminated by eggs or gravid proglottids
- Oncospheres hatch, penetrate intestinal wall, and circulate to musculature. Oncospheres develop into cysticerci in muscle.
- Humans infected by ingesting raw or undercooked infected meat
- Scolex attaches to intestine
Adults in small intestine
What is a trematode?
Helminth (eg schistosoma haematobium (bilharzia))
Infections of veins around bladder in humans. Causes bladder inflammation, haematuria. Intermediate host is freshwater snail. Diagnosis by urine microscopy for eggs
What is the life cycle of schistosoma spp?
- Eggs in freshwater
- Miracidium hatches from egg. Infects intermediate host – snail
- Cercariae leave snail, penetrate skin of human in water
- Immature worm enters the blood stream and ends up in veins near intestine or bladder
- Worms reach sexual maturity in veins of abdominal cavity, females produce eggs, eggs enter intestinal tract or bladder
Eggs passed in urine or faeces enter freshwater
what is a bedbug?
type of ectoparasite (eg Cimex Lectularius)
wingless insect - hides in cracks in furniture and walls. emerge to feed 5-10 minutes for blood meal. itchy rash after bite and can transmit other infections (protozoa in south america (trypanosomiasis))
what are the 2 main forms of fungus?
yeasts which are single cells which bud
moulds which are filamentous strands
some can switch between yeast + mould (dimorphic fungi)
what is a superficial fungal infection?
infection of skin and related structures eg tinea pedis (athlete’s foot), tinea corporis (ringworm). usually due to 3 common species of mould
what is a severe invasive fungal infection?
eg cryptococcus neoformans (yeast)
infects patients with low resistance due to failing immune system eg HIV.
causes meningitis. other symptoms: headaches, neck stiffness, confusion, coma, death
what is bacteria and what structures does it contain?
unicellular organism - prokaryote. has a cell membrane, cell wall, no nucleus, reproduce asexually and are able to move using flagellae and pili
which common severe infections in developed countries is bacteria responsible for?
- pneumonia
- UTI
- cellulitis
- meningitis
- clolecystitis
- diverticulitis
- appendicitis
what different forms can bacteria take up?
round - coccus rod - bacillus clusters chains pairs (diplococci)
how is bacteria classified?
using a gram stain. some retain crystal violet stain, others do not. gram-positive (purple), gram-negative (pink)
what is streptococcus pneumoniae aka pneumococcus?
bacterial infection. gram +ve coccus in pairs. colonise nose + throat. cause pneumonia when invade other sites eg lungs. symptoms: dirty sputum, chest pain, breathlessness, fever. complications: blood stream infection, meningitis, death
what is a virus?
it is dependent on infection of host cell for metabolism and replication. contains protein core surrounding genetic material (DNA or RNA), protein coat and maybe outer membrane. small - 1/100th size of bacteria. can only be seen by electron microscope
