Introduction to Parasites Flashcards
What is the definition of a parasite?
an organism which lives in or on another organism (its host) and benefits by deriving nutrients at the other’s expense
A parasite does not necessarily cause disease
What is the definition of a host?
an organism which harbours the parasite
What is meant by symbiosis?
What are the 3 types?
living together and a close long term interaction between two different species
this can be mutualism, parasitism or commensalism
What is meant by mutualism?
an association in which both species benefit from the interaction
What is meant by parasitism?
an association in which the parasite derives benefit and the host gets nothing in return, but always suffers some injury
What is meant by commensalism?
an association in which the parasite is deriving benefit without causing injury to the host
What are the 4 classes of host?
- definitive host
- reservoir host
- intermediate host
- paratenic host
What is a definitive host?
either harbours the adult stage of the parasite or where the parasite utilises the sexual method of reproduction
in the majority of human parasitic infections, man is the definitive host
What is meant by a reservoir host?
an animal or species infected by a parasite which serves as a source of infection for humans or other species
What is meant by an intermediate host?
harbours the larval or asexual stages of the parasite
some parasites require 2 intermediate hosts in which to complete their life cycle
What is meant by a paratenic host?
host where the parasite remains viable without further development
What are the 3 categories of parasites?
- protozoa
- platyhelminths and nemathelminths
- arthropoda
What are examples of protozoa?
- flagellates
- ameoboids
- sporozoans
- trypanosomes
What are examples of helminths?
- flat worms - flukes and tapeworms
- roundworms (nematodes)
What are examples of arthropoda?
- ectoparasites (lice and mites)
- blood sucking arthropods (mosquitoes)
What are the characteristics of protozoa?
they are single-celled organisms
they can be free-living or parasitic in nature and multiply in humans
How do GI and blood parasites in the protozoa phylum tend to be transmitted?
GI parasites are transmitted via the faecal-oral route
Blood parasites are transmitted via arthropod vector
What are examples of flagellates?
- giardia lamblia
- trichomonas vaginalis
What are examples of amoeboids?
- entamoeba sp.
- acanthamoeba sp.
What are examples of sporozoans?
- plasmodium sp.
- cryptosporidium sp.
- toxoplasma sp.
What are examples of trypanosomes?
- trypanosoma sp.
- leishmania sp.
What are helminths?
How do they multiply within humans?
they are large multicellular organisms
adults are generally visible by eye
adults cannot multiply in humans
What are the 2 types of platyhelminths (flatworms)?
Cestodes (tapeworms):
- Taenia sp.
- Echinococcus sp.
Trematodes (flukes):
- Schistosoma sp.
What are the different types of nematodes (roundworms)?
Intestinal nematodes:
- Ascaris sp.
- trichuris sp.
Tissue nematodes:
- wuchereria sp.
- onchocerca sp.
What are the two types of ectoparasites?
blood sucking arthropods and those that burrow into the skin
arhtropods are important transmitters of infection
What are the 4 main categories of ectoparasites?
- insects
- lice
- mites
- arachnids (ticks)
What are the 6 stages in how to approach parasites?
distribution:
- where we find them
life cycles:
- how they survive and breed
clinical manifestations:
- how they affect the host
diagnosis:
- how we identify them
treatment:
- how we get rid of them
control:
- how we prevent others from getting infected
What are the 3 different types of life cycle?
- direct
- simple indirect
- complex indirect
What are the stages in this direct lifecycle?
What are the stages in the indirect lifecycle?
What are the stages in this complex indirect lifecycle?
What type of parasite is ascarisasis?
macroparasite
intestinal nematode
In which group is the peak prevalence of ascariasis seen?
How is it acquired?
peak prevalence in 3-8 year olds
seen in areas of poor hygiene
acquired by ingestion of eggs
What happens when there is lung migration of ascariasis?
Loefflers syndrome
- dry cough
- dyspnoea
- wheeze
- haemoptysis
- eosinophilic pneumonitis
What are the consequences of the intestinal phase of ascariasis?
- malnutrition
- malabsorption
- migration into hepatobiliary tree and pancreas
- intestinal obstruction
- worm burden
What is the treatment for ascariasis?
How does it work?
albendazole
this prevents glucose absorption by the worm
the worm starves and detaches itself
What type of parasite is schistosomiasis sp.?
macroparasite
(helminth, platyhelminth, trematode/fluke)
it is also known as Bilharzia
What does Schistosomiasis sp. cause?
What is the intermediate host?
it causes chronic disease resulting in bladder cancer and liver cirrhosis
snails are the intermediate host
What are the stages in the life cycle of schistosomiasis?
What is the initial infection incubation period in schistosomiasis?
14 - 84 days incubation period
What are the symptoms of schistosomiasis infection?
it is often asymptomatic
Katayama syndrome is a symptomatic acute infection:
- rash and fever
- headache and myalgia
- respiratory symptoms
- often with eosinophilia and hepato- and/or splenomegaly
What are the other clinical features of schistosomiasis?
- swimmers itch
- katayama fever
- chronic schistosomiasis can persist for years
- effect of eggs on distant sites - e.g. lungs, spine
What organisms can cause hepatic/intestinal schistosomiasis?
S. mansoni
S. intercallatum
S. japonicum
S. mekongi
What organism causes urinary schistosomiasis?
What can this lead to?
S. haematobium
- haematuria
- bladder fibrosis and dysfunction
- squamous cell cancer
What can hepatic/intestinal schistosomiasis lead to?
- portal hypertension
- liver cirrhosis
- abdominal pain
- hepatosplenomegaly
What are the main public health risks associated with schistosomiasis?
- undernutrition due to the suppression of appetite and inflammation-mediated cachexia
- anaemia
- renal failure
- bladder tumours
- hepatic fibrosis and associated increased risk of oesophageal varices
How does schistosomiasis affect sexually transmitted diseases and pregnancy?
- increased risk of transmission of HIV
- poor birth outcomes in maternal infection and association with decreased birth weight
How is schistosomiasis diagnosed?
urinary:
- terminal stream microscopy
- serology
hepatic/intestinal:
- stool microscopy
- rectal snip microscopy
- serology
What is the main treatment for schistosomiasis?
Praziquantel
20 mg/kg x 2 doses 4-6 hours apart
(3 doses in S japonicum)
What are the characteristics of Praziquantel?
How does it work?
it is well absorbed with an extensive 1st pass metabolism
inactive metabolites are excreted in urine
the mechanism of action is unknown
What steps are taken in the control of schistosomiasis?
- chemical treatment to kill snail intermediate hosts
- chemoprophylaxis
- avoidance of snail infested waters
- community targeted treatment, education and improved sanitation
What is hydatid disease?
What is it caused by?
macroparasite (platyhelminth - cestode - tapeworm)
the usual hosts are sheep and dogs (humans are an accidental host)
it is caused by Echinococcus sp.
What are the clinical effects of hydatid disease?
- cysts - 70% in liver and 20% in lungs
- may remain asymptomatic for years
- mass effect - cysts remain asymptomatic until a certain size is reached
- secondary bacterial infection
- cyst rupture - hypersensitivity
How is hydatid disease diagnosed?
- serology
- histology (if cyst ruptures)
no not biopsy or aspirate, as rupturing the cyst increases the risk of spread
What is the treatment for hydatid disease?
Albendazole
Prazigantel is used for daughter cysts
What is the appearance of a hydatid cyst like?
a ruptured hydatid has a classic waterlily appearance
What are the missing stages in hydatid control?
What are the 5 species of malaria?
What type of parasite is it?
microparasite (protozoa - sporozoan)
4 human species:
- P. falciparum
- P. vivax
- P. ovale
- P. malariae
1 monkey species:
- P. knowlesi
What are most cases of malaria caused by?
2000 cases a year in the UK due to travel
70% of these are due to P. falciparum
What is the vector involved in malaria?
Anopheles mosquito
What is the clincal background behind the symptoms of malaria?
parasites rupture red blood cells, block capillaries and cause an inflammatory reaction
What are the symptoms of malaria?
- fever and rigors
- cerebral malaria - confusion, headaches, coma
- renal failure in black water fever
- hypoglycaemia
- pulmonary oedema
- circulatory collapse
- anaemia, bleeding and DIC
How do the patterns of fever and rigors vary in malaria?
they are alternative days in falciparum malaria
they are every 48hrs or 72hrs with benign malaria
What are the differences in time frames of the erythrocytic cycle in different types of malaria?
P knowlesi - 24 hrs
P falciparum, P. vivax, P ovale - 48 hrs
P. malariae - 72 hrs
What is an important clinical thing to remember about malaria when seeing patients?
returning traveller + fever = malaria
until proven otherwise
(also think about viral haemorrhagic fever)
How is malaria diagnosed?
thick and thin microscopy
serology is used for detection of the antigen in the blood
PCR is used for detection of malarial DNA
When are antimalarials used to treat malaria?
What are the different types?
used in Falciparum malaria
co-artem:
- artemether/lumefantrine
- atovaquone - proguanil
complicated:
- IV artesunate
- must complete a full oral course when able to stop IV
What is the problem with IV artesunate treatment and how should it be monitored?
haemolysis occurs in 10-15% of patients following IV artesunate treatment
haemoglobin concentrations should be checked 14 days after treatment
What is the purpose of supportive therapies in malaria treatment?
- management of seizures, pulmonary oedema, acute renal failure and lactic acidosis
- exchange transfusion is used in hyperparasitaemia
What is the firstline treatment for non-falciparum malaria?
oral chloroquine
25mg base/kg over 3 days
the usual dose in adults is 10 tablets in total
What is the treatment in non-falciparum malaria if the patient cannot tolerate oral chloroquine?
if the patient is vomiting and unable to tolerate oral chloroquine then IV quinine is given
when the patient can swallow, the FULL COURSE of chloroquine is completed
When is primaquine used in malaria treatment?
Vivax and Ovale need primaquine 14 days to treat liver
this prevents recurrence (check G6PD status)
What steps are involved in control of malaria?
- insecticide spraying in homes
- larvicidal spraying on breeding pools
- filling in of breeding pools
- larvivorous species introduced into mosquito breeding areas
- insecticide impregnanted bed nets
- chemoprophylaxis before travelling
What is the distribution of strongyloidiasis like?
transmission occurs mainly in tropical and subtropical regions but also in temperate climates
What is significant about the lifecycle of strongyloidiasis?
autoinfection
the larvae in the large intestine penetrate intestinal mucosa or perianal skin and migrate randomly to other organs
this causes the infection to be ongoing
What is the public health risk associated with strongyloidiasis?
strongyloidiasis hyperinfection syndrome has mortality rates up to 90%
Strongyloides spp. can be sexually transmitted in the MSM community
How is strongyloides diagnosed?
- serology
- stool culture through charcoal filtration method
How is strongyloides hyperinfection syndrome diagnosed?
it can be difficult as serology and direct microscopy are often negative
stool culture/concentration methods are required
What is the treatment for strongyloides?
Ivermectin ug/kg for 2 days
OR
albendazole 400mg for 7 days
What is the treatment of hyperinfection syndrome/disseminated strongyloidiasis?
if possible, stop or reduce immunosuppressive therapy
Ivermectin
200 ug/kg per day orally until stool and/or sputum is negative for 2 weeks
What are the steps involved in strongyloides control?
- wear shoes when walking on soil
- avoid contact with faecal matter or sewage
- proper sewage disposal and faecal management
What is cryptosporidiosis caused by?
How is it spread?
microparasite (sporozoan)
Caused by Cryptosporidium parvum and hominis
causes diarrhoeal disease and is transmited through faecal-oral spread
can also have human to human spread with animal reservoir
Where is cryptosporidiosis most common?
worldwide distribution but is more common in temperate and tropical countries
What is the incubation period for cryptosporidiosis?
what are the associated symptoms?
incubation period is normally 7 days (can be 2-10 days)
- watery diarrhoea with mucus (no blood)
- bloating and cramps
- nausea and vomiting
In which groups can cryptosporidiosis be severe?
it is usually self-limiting and lasts up to 2 weeks
it can be very severe in:
- very old and very young
- immunocompromised
Who is at risk of cryptosporidiosis by human-human spread?
- regular users of swimming pools
- child care workers and parents
- nursing home residents/carers
- healthcare workers
- travellers
who is at risk of cryptosporidiosis through animal-human spread?
- backpackers, campers, hikers
- farm workers
- visitors to farms/petting zoos
- consumers of infected dairy products
How is cryptosporidiosis diagnosed?
- acid fast staining in faeces sample
- antigen detection by EIA
What is the treatment in symptomatic cryptosporidiosis?
- rehydration and drinking more fluid
- nitazoxanide
What are the treatments for cryptosporidiosis in immunocompromised individuals?
- paromycin to kill parasite
- nitazoxanide
- octreotide to reduce cramps and frequency
- HAART should be quickly initiated in HIV patients
in severe cases, a combination of paromycin, nitazoxanide and azithromycin is used
What is trichomoniasis caused by?
How is it transmitted?
Trichomonas vaginalis
it is a sexually transmitted flagellated protozoan
incubation period is 5-28 days
What are the symptoms of trichominiasis?
men are asymptomatic
women:
- smelly vaginal discharge
- dyspareunia (painful sex)
- dysuria
- lower abdominal discomfort
- punctuate haemorrhages on cervix (“strawberry cervix”)
How is trichomoniasis diagnosed?
identification of organism in genital specimens on direct microscopy
PCR
What is the treatment of trichomoniasis?
Metronidazole
single dose of 2g for 5-7 days
treat partner simultaneously
What is the prevention methods for trichomoniasis?
- general advice about prevention of STIs
- use of barrier contraceptive methods if sexually active
What is giardiasis and how is it transmitted?
flagellated protozoan transmitted through faecal-oral transmission
What are the symptoms of giardiasis?
How long do they last?
it can range from asymptomatic carriage to severe diarrhoea and malabsorption
symptoms usually lasdt 1-3 weeks
- diarrhoea
- abdominal pain
- bloating
- nausea and vomiting
How is giardiasis diagnosed and treated?
Diagnosis:
- identification of cysts or trophozoites in faeces
Treatment:
- metronidazole
- tinidazole
What is involved in the prevention of giardiasis?
- no vaccine is available
- hygiene measures
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