6. Parasitic infections Flashcards
1
Q
What is an infection and disease?
A
Infection - invasion and growth of pathogenic microorganisms within the body
Disease - disordered or incorrectly functioning organ, structure or system of the body resulting from the effect of genetics/developmental errors, infections, poisons, nutritional imbalance, toxicity or environmental factors / illness
2
Q
What is a vector?
A
Organism that transmits a disease or parasite from one animal or plant to another
3
Q
What is a parasite?
A
Organisms living in or on the host and dependent on it for nutrition, causing damage
4
Q
What are parasite that live in or on the host called?
A
In - endoparasites
On - ectoparasites
5
Q
Describe Protozoa
A
- Endoparasitic
- Single-celled
- Eukaryotes (genome in a nucleus, have complex organelles in cytoplasm)
- Varied pathogenesis
- Not characterised by eosinophilia
6
Q
Give examples of protozoan parasites
A
- Amoebae e.g. Entamoeba histolytica
- Coccidian e.g. Toxoplasma
- Ciliates e.g. Balantidium coli
- Flagellates e.g. Giardia
7
Q
Describe Metazoa
A
- Endoparasitic
- Multicellular - helminths/worms
- Some just inhabit the gut (geohelminths), others invade tissues
- Characterised by eosinophilia, if it invades the blood
8
Q
How does infection by amoebae occur?
A
Ingestion of mature cysts in food or water, or on hands contaminated by faeces
9
Q
Where does amoebae rank in causes of death by parasitic infections and what is the animal reservoir for infection?
A
- 3rd most common cause of death
- Humans are the only reservoir
(90% are asymptomatic)
10
Q
Describe how amoebae infects humans
A
- Cysts enter the small intestine and release active parasites (trophozoites)
- These invade the epithelial cells of the large intestines, causing flask-shaped ulcers
- Can spread to other organs e.g. liver, brain etc. via venous system
- Asymptomatic carriers pass cysts in faeces (can remain viable for 2 months)
11
Q
What problems does invasive amoebiasis most often cause, and which species causes this?
A
Amoebic liver abscess
caused by E. histolytica, not E. Dispar, which is commensal
12
Q
What do the following Coccidia cause:
• Plasmodium
• Toxoplasma
• Cryptosporidium
A
- Plasmodium - malaria
- Toxoplasma - toxoplasmosis: mild disease in immunocompetent individuals, but danger in pregnancy
- Cryptosporidium - diarrhoea
13
Q
What are the different types of Plasmodium?
A
- P. falciparum
- P. knowlesi
- P. ovale
- P. vivax
- P. malariae
14
Q
What are the 2 types of hosts for Plasmodium?
A
Humans and female Anopheles mosquitoes
15
Q
How many mosquito and human stages are there of the malaria life cycle?
A
1 mosquito and 2 human
16
Q
What are the human stages of the malaria life cycle?
A
1) Liver stage - parasite invades liver cells, multiplies, ruptures
2) Blood invasion
17
Q
When do symptoms generally appear for malaria?
A
- Can appear as early as 7 days
* Time between exposure and signs of illness can be as long as one year
18
Q
When do symptoms appear for the following: • P. falciparum • P. knowlesi • P. ovale • P. vivax • P. malariae
A
- P. falciparum - 9-14 days
- P. knowlesi - 11-12 days
- P. ovale - 12-18 days
- P. vivax - 12-18 days
- P. malariae - 18-40 days
19
Q
What are the symptoms of malaria?
A
- Fever, headache, chills, vomiting, muscle pain
* Paroxysm (cycle in 4 to 8 hours)
20
Q
What are the complications of malaria?
A
- Severe anaemia
- Cerebral malaria (swelling of brain, seizures, coma)
- Liver failure
- Shock
- Pulmonary oedema
- Low blood sugar
- Kidney failure
- Swelling/rupture of the spleen
21
Q
What is the treatment for uncomplicated and severe malaria?
A
Uncomplicated • Chloroquine • Atovaquone-proguanil • Artemether-lumerfantrine • Quinine sulfate • One of: doxycycline, tetracycline etc.
Severe
• Artemisinin-based combination therapy (ACT) for P. falciparum malaria
22
Q
How can you diagnose malaria?
A
- Blood film, Giemsa stained microscopy
- Detect the type by looking at the shape of the parasite
- P. falciparum is the worst
• Antigen detection tests are faster, but more expensive and less sensitive
23
Q
How can humans become infected by toxoplasma?
A
- Eating undercooked meat
- Consuming food or water contaminated with cat faeces
- Contaminated environmental samples
- Blood transfusion, organ transplant, transplacental
24
Q
What complications may occur in immunocompromised patients with toxoplasma?
A
CNS disease, brain lesions, pneumonitis, retinochoroiditis
25
Who does toxoplasma infect and how can you test it?
* Warm-blooded animals
| * Serological test
26
What does cryptosporidium cause?
* May not realise you have it if you are healthy
| * If immunocompromised: diarrhoea, fever, nausea, vomiting
27
What is the route of infection, diagnosis and treatment for cryptosporidium?
* Route: faecal-oral route
* Diagnosis: stool examination
* Treatment: fluid rehydration
28
What is Balantidiasis and what does it cause?
* Ciliate
* Asymptomatic in most people
* Dehydrating in HIV patients (diarrhoea, dysentery, abdominal pain, weight loss, nausea, vomiting)
* Colon perforation if untreated
29
What is the diagnosis for Balantidiasis?
Stool examination
30
What is Giardia, how is it acquired and what does it cause?
* Flagellate
* Attache by their suckers to the surface of the duodenal or jejunal mucosa
* Ovoid cysts can survive the standard chlorination procedure, but trophozoite can't
* Filtration required remove them, can acquire from unfiltered water
* Transmitted via faecal-oral route
* Mostly asymptomatic
* Acute symptoms: can cause diarrhoea, greasy stools, abdominal cramps, nausea, dehydration
31
How is Giardia diagnosed and treated?
Diagnosis: stool examination
Treatment: metronidazole/tinidazole
32
How is trichomonas transmitted and what are the symptoms?
* Flagellate transmitted sexually
* Can be asymptomatic (up to 50%)
* Women: vaginal discharge, vulval itching, dysuria, offensive odour, low abdominal discomfort
* Males: discharge, dysuria
33
What are the complications of trichomonas?
Detrimental outcome on pregnancy, associated with pre-term delivery and low birth weight
34
What effect does trichomonas have on HIV?
Enhance HIV transmission, and increase risk of trichomonas in those with HIV
35
What is the diagnosis and treatment for trichomonas?
Diagnosis: microscopy (swab/urine) and rapid test
Treatment: metronidazole
36
What are helminths and their definitive host?
* Metazoa
* Complex multicellular parasites
* Humans are the definitive host (few are zoonoses)
37
What is the most common worm infection worldwide?
Ascariasis
38
What are the 3 different types of worm and give examples?
* Roundworms (Nematodes) e.g. Ascaris
* Flatworms (Cestodes) e.g. Taenia
* Flukes (Trematodes) e.g. Schistoma
39
```
For Ascaris (roundworm):
• Where do they live?
• When do eggs become infective?
• How are the larvae carried?
```
* Live in lumen of small intestine
* Eggs embryonate and become infective after 18 days - several weeks
* Larvae hatch and invade the intestinal mucosa
* Carried via the portal then systemic circulation to the lungs
* Mature in the lungs for 10-14 days
* Penetrate into alveoli
* Ascend the bronchial tree to the pharynx
* Swallowed and reach the small intestine
40
How long can adult Ascaris worms live for?
1-2 years
41
What are the symptoms of Ascaris infection?
* Often asymptomatic
* Large number may cause abdominal pain or intestinal obstruction
* Problems in malnourished individuals as they feed on contents of small intestine
* Localised reactions in various organs from larvae migration
* Loeffler's pneumonia from lung penetration - blood and dead epithelial cells can clog air spaces
* Secondary bacterial infections
42
What is the diagnosis and treatment for Ascariasis and hookworms?
Diagnosis: stool examination
Treatment: albendazole and mebendazole
43
Describe hookworms (roundworm) e.g. Ancylostoma duodenale and what they can cause
* 1cm long and curved
* Buccal capsules that attach them to the vili of the small intestine
* Hard to expel and can cause intestinal bleeding - iron deficiency anaemia
* GI and metabolic symptoms
* Local skin manifestations during penetration
* Respiratory symptoms during pulmonary migration
44
How do hookworms e.g. Ancylostoma duodenale enter the body and reside in the small intestine?
* Initially enters body through skin e.g. sole of foot
* Larvae carried through the blood vessels to the heart and lungs
* Penetrate alveoli and ascend the bronchial tree to the pharynx
* Swallowed and reach the small intestine
45
How does the hookworm Trichuris trichuria (whipworm) grow in a human and where do they live?
* Faecal-oral transmission
* Eggs hatch in the small intestine and release larvae
* Larvae mature and establish themselves as adults in the colon
* Adult worms live in the caecum and ascending colon
46
What are the symptoms of a whipworm?
* Asymptomatic if small amount
| * If there's a lot - bloody diarrhoea, anaemia, open wounds (intestinal inflammation), rectal prolapse
47
Which worm is being used in helminthic therapy, to help against allergies and autoimmune diseases?
Whipworm
48
How does the nematode, Lymphatic filariasis, cause its symptoms?
* Blocks lymphatic vessels
* Can progress to elephantiasis
* Can occur in the legs (and arms, breast and scrotum)
49
How is Lymphatic filariasis transmitted?
* Mosquito takes up blood from infected host with the microfilariae
* Larvae transform in the mosquito
* Transfers to another person
50
What is the diagnosis and treatment for Lymphatic filariasis?
Diagnosis: blood smear/antigen detection with immunochromatic test / ELISA
(peak amounts in peripheral blood from 10pm - 4am)
Treatment: albendazole and ivermectin
51
What transmits the nematode Loa Loa (filaria), what does it cause and how long can it live in a person?
• Transmitted by a fly (becomes infective in the fly)
* Loiasis
* Migrate through subcutaneous tissues and cross the front of the eye under conjunctiva
• Lives for 4-12 years
52
What are the definitive hosts for the (cestode) tapeworm Taenia spp., how can it be acquired and what are the symptoms?
* Humans
* Eating raw meet (eggs can survive in environment for months)
* T. saginata (from beef) can cause more symptoms than the other types - size up to 10m
* Mostly asymptomatic
* Abdominal pain, loss of appetite, weight loss, upset stomach
* Most common acquired cause of epilepsy (can cross the BBB)
53
What is the most visible sign of taeniasis?
Active passing of tapeworm segments
54
What is the treatment for Taenia spp.?
Praziquantel
55
How does Schistosomiasis (trematode) transfer to a human?
* Eggs eliminated in water via faeces or urine
* Hatch and release miricidia
* Penetrate a snail, transform and release cercariae in the water
* This can penetrate the skin and migrate through tissues, transforming into an adult
* Eventually resides in venules
* Eggs move progressively towards the lumen of the intestine (S. mansoni/japonicum) or the bladder/ureters (S. haematobium)
56
What are the symptoms of Schistosomiasis?
Days
• Rash or itchy skin
```
1-2 months (mostly asymptomatic)
• Fever
• Chills
• Cough
• Muscle aches
```
(inflammation or scarring in the intestine/liver/bladder)
57
How is Schistosomiasis diagnosed and treated?
Diagnosis: stool or urine samples
Treatment: praziquantel
(Can be prevented by killing the snails with Endod berries)
58
What are the common names for the following ectoparasites:
• Pediculus humanus capitis
• Pediculus humanus corporis
• Pthirus pubis
* Pediculus humanus capitis - head louse
* Pediculus humanus corporis - body louse
* Pthirus pubis - pubic louse
59
What are the 3 stages of the life of lice?
* Eggs
* Nymphs
* Adult
60
What type of parasite is Leishmania and how is it transmitted into the body?
Protozoan flagellate parasite
Vector - sandfly
• takes blood meal
• regurgitates parasite into mammalian host
• taken up by phagocytic cells
• transforms into non-flagellated form
• parasite dies and amastigote form is released into blood
61
Describe the 2 forms of leishmania
Promastigote
• Transmitted by the sandfly
• Has a flagellum
• Form of leishmania within the sandfly
Amastigote
• Acheived inside the phagocytic cell
• Form within humans or other vertebrate host cells
• Resorbed their flagellum - no longer motile
62
How are sandflies different to mosquitos?
Attack is silent - cannot be heard
63
Describe the most severe form of Leishmaniases
Visceral leishmaniasis (black fever)
• Irregular fever, weight loss, hepato/splenomegaly, anaemia
• Affects internal organs
• Risk factors: malnutrition, immunosuppression
64
How can Leishmaniasis be diagnosed?
* Parasite detection - visualisation of the amastigote form by microscopy
* Antibody detection - direct agglutination test (DAT) and rK39 chromatographic test
65
What are the 3 categories of cutaneous leishmaniasis?
* Localised
* Diffuse
* Mucocutaneous
66
Describe localised cutaneous leishmaniasis
* Skin lesions on exposed body parts
* Can create serious disability and scars (can be disfiguring) - causes social problems
* Can heal
* Immunity to reinfection
67
Describe diffuse cutaneous leishmaniasis
* Disseminated lesions characterised by nodules (non-ulcerating lesions)
* Resembles leprosy, difficult to treat
* No spontaneous healing
* Nodules are full of parasites
* Relapses
68
Describe mucocutaneous leishmaniasis
* Disfiguring, destroys mucous membranes
* Very severe
* No spontaneous healing
* Relapses
* Malnutrition is a serious manifestation (hurts to eat)
69
What is the diagnosis and treatment for cutaneous leishmaniasis?
Diagnosis: microscopy and culture, PCR
Treatment: Sodium stibogluconate (SSG)
