Parasites Flashcards
Define symbiosis
living together; close, long term interaction between two different species
Define Mutualism
an association in which both species benefit from the interaction
Define parasitism
an association in which the parasite derives benefit and the host gets nothing in return but always suffers some injury
Define commensalism
an association in which the parasite only is deriving benefit without causing injury to the host
What is a definitive host?
Either harbours the adult stage of the parasite or where the parasite utilizes the sexual method of reproduction In the majority of human parasitic infections, man is the definitive host
What is an intermediate host?
Harbours the larval or asexual stages of the parasite Some parasites require two intermediate hosts in which to complete their life cycle
What is a paratenic host?
Host where the parasite remains viable without further development
What are the two main types of parasites that cause disease in humans?
Protozoa (micro-parasites) Helminths (macro-parasites)
What are the 4 main types of protozoa?
Flagellates Amoeboids Sporozoans Trypanosomes
Name 5 sporozoans
Plasmodium sp Cryptosporidium sp Cyclospora sp Isospora sp Toxoplasma sp
Name 2 amoeboids
Entamoeba sp Acanthamoeba sp
Name 2 trypanosomes
Trypanosoma sp Leishmania sp
Name a flagellate
Guardia Iamblia
What are 2 types of helminth?
Flatworms (Platyhelminths) Roundworms (Nematodes)
What are the 3 types of life cycle?
Direct Simple indirect Complex indirect
What is an example of a direct life cycle?
What is an example of an indirect life cycle?
What is an example of a complex life cycle?
What is ascariasis?
- Macroparasite: Intestinal nematode, Ascaris lumbricoides
- More than 1 billion people affected worldwide (approximately 1/7 world population)
- Peak prevalence in 3-8 year olds
- Areas of poor hygiene
- 1 adult worm can produce 200,000 eggs per day
- Acquired by ingestion of eggs
What is the life cycle of ascariasis?
What are the clinical features of ascariasis?
Lung Migration:
- Loefflers syndrome- dry cough, dyspnea, wheeze, haemoptysis, eosinophilic pneumonitis
Intestinal Phase:
- Malnutrition
- Migration – into hepatobiliary tree and pancreas
- Intestinal obstruction
- Worm burden
How is ascariasis treated?
Albendazole
- Benzimidazole
- Prevents glucose absorption by worm
- Worm starves-detaches-passed PR
What is schistosomiasis?
- Macro-parasite (Helminth- Platyhelminth- Trematode/Fluke)
- Also known as Bilharzia disease
- Estimated that 200 million people effected worldwide (predominantly in Africa)
- Caused by fluke, Schistosoma:
- S. haematobium
- S. mansoni
- S. intercallatum
- S. japonicum
- S. mekongi
- Causes chronic disease resulting in bladder cancer and liver cirrhosis
- Snails as intermediate host
What does the life cycle of schistosomiasis look like?
What are the clinical features of schistosomiasis?
Urinary (S. haematobium)
- Haematuria
- Bladder fibrosis and dysfunction
- Squamous cell CA bladder
Hepatic/Intestinal (S. mansoni; S. intercallatum, S. japonicum; S. mekongi)
- Portal Hypertension
- Liver cirrhosis
How is schistosomiasis diagnosed?
Urinary
- Terminal Stream Microscopy
- Serology
Hepatic/Intestinal
- Stool Microscopy
- Rectal Snip Microscopy
- Serology
How is schistosomiasis treated?
- Praziquantel (parazinoisoquinoline derivative)
- 40-60 mg/kg with food 3 doses 8-hourly
- Mechanism unknown- increased ionic permeability tetanic contraction, detachment, death
- Well absorbed, extensive 1st pass metabolism, inactive metabolites excreted in urine
- Treatment of long term complications
What is hydatid disease?
- Macro-parasite (Platyhelminth- Cestode-Tapeworm)
- Human is accidental host
- Usual hosts are sheep and dogs
- Found all over the world wherever sheep are farmed
- Caused by Echinococcus sp. (E. granulosus- cystic and E. multilocularis- alveolar)
What does the life cycle of hydatid disease look like?
What are the clinical features of hydatid disease?
- Cysts: 70% liver, 20% lungs
- May remain asymptomatic for years
- Mass effect
- Secondary bacterial infection
- Cyst rupture- hypersensitivity
How is hydatid disease diagnosed?
Imagin and serology
How is hydatid disease controlled/prevented?
- Regularly worm dogs to reduce egg production
- Hand hygiene
- Safe disposal of animal carcasses/products of conception
What is Malaria?
- Micro-parasite (protozoa- sporozoan)
- 4 species of Plasmodium:
P. falciparum
P. vivax
P. ovale
P. malariae
- 300-500 million people infected every year
- 1-3 million deaths per year, mainly in young children
- ~2000 cases/year in UK – 70% P. falciparum
(Travel clinic)
What does the life cycle of malaria look like?
What are the clinical features of malaria?
Parasites rupture red cells, block capillaries and cause inflammatory reaction
- Fever & Rigors (alt. days with falciparum malaria, every 48hrs or 72hrs with benign malaria)
- Cerebral malaria (confusion, headache, coma)
- Renal failure (black water fever)
- Hypoglycaemia
- Pulmonary oedema
- Circulatory collapse
- Anaemia, Bleeding and DIC
How is malaria diagnosed?
- Thick and Thin Microscopy
- Serology- detection of antigen in blood
- PCR- detection of malarial DNA
How is malaria treated?
How is malaria controlled/prevented?
- Insecticide spraying in homes
- Larvicidal spraying on breeding pools
- Filling in of breeding pools
- Larvivorous species introduced in to mosquito breeding areas
- Use of insecticide impregnated bed nets
- Chemoprophylaxis
- ??Vaccine??
What is cryptosporidiosis?
- Caused by Cryptosporidium parvum and hominis (micro-parasite, sporozoan)
- Causes diarrhoeal disease
- Human to human spread with animal reservoir (cattle, sheep, goats)
- Faecal-oral spread
- World wide distribution (esp. temperate and tropical)
- Sporadic cases or lead to outbreaks
What does the life cycle of cryptosporidiosis look like?
What are the clinical features of Cryptosporidiosis?
- Incubation 2-10 days (usually 7 days)
- Watery diarrhoea with mucus (no blood)
- Bloating, cramps, fever, nausea, vomiting
- Usually self-limiting (last up to 2 weeks)
- Can be severe in:
- very young
- very old
- Immuno-compromised (60% HIV patients infected go on to chronic infection- can loose up to 25 litres fluid/day)
Who is at risk of Cryptosporidiosis?
Human-Human Spread:
- Regular users of swimming pools (can be resistant to chlorine)
- Child care workers and parents
- Nursing Home residents/carers
- Healthcare workers
- Travellers
Animal-Human Spread:
- Backpackers, Campers, Hikers
- Farm workers
- Visitors to farms/petting zoos
- Consumers of infected dairy products
How is Cryptosporadiosis diagnosed?
•Faeces sample:
Acid fast staining
Antigen detection by EIA
How is Cryptosporidiosis treated?
Symptomatic:
- Rehydration etc.
- Nitazoxanide
For immunocompromised:
- Paromomycin (to kill parasite)
- Nitazoxanide (effectiveness is unclear)
- Octreotide (reduce cramps and frequency)
- HIV patients, HAART should be quickly initiated
How is cryptosporidiosis controlled/prevented?
What are some common anti protozoal treatments?
- Metronidazole
- Pentamidine
- Nitazoxanide
- Pyrimethamine
- Anti malarials
- treatment
- prophylaxis
What are some common anti-helminthic drugs?
- Albendazole
- Mebendazole
- Ivermectin
- Praziquantel
