Parasitology Flashcards
Onchocerciasis - organism
Onchocerca volvulus
Onchocerciasis - geographical distribution
Africa
Onchocerciasis - transmission
Simulium (blackflies) that are day biting outdoors and breed in rapids
Onchocerciasis - life cycle
- Blackfly with L3 larvae bites human and injects into skin
- L3 larvae migrate to the subcutaenous tissue and mature into adult worms, forming nodules
- Adult worms produce microfilariae which migrate to the skin and eyes causing symptoms
- Blackfly ingests Mf
- L1 –> L3 larvae in the blackfly midgut
Onchocerciasis symptoms
Itching
Skin nodules and can develop atrophy, lizard skin chronically
Eye disease - punctate keratitis, anterior uveitis, secondary cataracts, optic atrophy
Late stage - retinal changes, sub-conjunctival haemorrhage
Epilepsy
Poor growth
Onchocerciasis - diagnostics
Skin snip
Antibody testing (Ov16)
Onchocerciasis - treatment
Ivermectin - although does not kill adult worms and cannot give in concurrent loa loa infection
Doxycycline to eradicate Wolbachia
Onchocerciasis - prevention
- Blackfly vector control - insecticides
- MDA
- Cross border collaboration
What are the two types of helminths?
Platyhelminths (like a flattened patty-cake) –> Flat worms (flukes and tapeworms)
Nematodes - Round worms
Intermediate host (helminths)
Hosts the larval stage
Definitive host
Hosts the sexually mature adult
Cestodes = ribbon-like flat worms
What are the most important species?
Taenia saginata (beef tapeworm)
Taenia solium (pork tapeworm) (larval infection=cysticercosis)
Dihyllobothrium spp (fish tapeworm)
Echinococcus spp (dog and fox tapeworms) (larval infection=hydatid cyst)
Nematodes - what are the most important species?
Intestinal:
Hookworm
Ascaris
Trichuris
Strongyloides
Subcutaneous tissue:
Wucheria bancrofti
Brugia
What is Chagas disease?
A parasitic infection caused by trypanosoma cruzi, transmitted by triatoma bugs (rhodnius and panstrongylus)
Chagas disease - life cycle
- Triatoma bug bites and there is faecal inoculation
- Tryponmatigotes penetrate cells at the bite wound site and inside the cells they turn into amastigotes
- Intracellular amastigotes turn into trypomastigotes
Chagas disease transmission
Triatoma bug bite
Vertical transmission
Oral ingestion
Transplants/transfusion
Chagas - diagnostics
Serology (x2 - ELISA and IFAT)
PCR
Microscopy
Chagas symptoms
GI: Dysphagia, mega-oesophagus
Cardiac: Heart block, cardiomyopathy and heart failure
In immunocomprimised: fever, rash, myocarditis and SOL in HIV
Chagas treatment
Benznidazole 60 days
Side effects: Rash, numbness/peripheral neuropathy, weight loss
What is romana’s sign?
T cruzi infection through the conjunctiva
Management of asymptomatic Chagas
Consider benznidazole 60 days to prevent vertical transmission, in immunocompromised or immunocompetent with asymptomatic disease
ECG screening +/- echocardiogram
Hookworm - organism
Ancyclostoma duodenale
Necator americanus
Hookworm - transmission
Penetration of skin by L3 larvae
Oral ingestion of unwashed vegetation with L3 larvae on
Hookworm lifecycle
- Filariform larva penetrates the skin
- Exit circulation in the lungs
- Coughed up and swallowed into the intestine
- Eggs leave in the faeces
- Larvae atched and develop into a filariform larva in the environment
Hookworm - skin features
- Ground itch
- Cutaneous larva migrans (from cat + dog hookworm only as it cannot complete the lifecycle)
Hookworm - lung clinical features
Dry cough/wheeze
Loeffler’s syndrome (eosinophilic pneumonitis)
Hookworm - abdominal clinical features
Nausea, abdo pain, diarrhoea
Anaemia
Cognitive impairment in children
Hookworm - diagnostics
Stool OCP
60microns, thin wall like a pencil
Hookworm treatment
Albendazole or mebendazole
Ivermectin
Strongyloides - organism
Strongyloides stercoralis
Strongyloides - transmission
Penetration through the skin, often the soles of the feet
Strongyloides hyperinfection
Driven by autoinfection in the context of immunosuppression
Asexual reproduction by adult females in the gut –> L3 larvae can autoinfect internally through the intestinal mucosa or externally via perianal skin
Leading to disseminated strongyloides in multiple organs
Associations: Steroids, HTLV1, transplant. NOT HIV
Strongyloides skin manifestation
Pruritic dermatitis at site of initial penetration
Urticarial rash in the context of autoinfection
Cutaneous larva currens
Differentials for migratory swellings (9)
- Cutaneous larva migrans (Ancylostoma braziliense, Ancylostoma caninum).
- Strongyloidiasis (Strongyloides stercoralis).
- Gnathostomiasis (Gnathostoma spp.).
- Loiasis (Loa loa).
- Dracunculiasis (Dracunculus medinensis).
- Toxocariasis (Toxocara canis, Toxocara cati).
- Filariasis (Mansonella spp., Wuchereria bancrofti, Brugia malayi).
- Fascioliasis (Fasciola hepatica).
- Trichinosis (Trichinella spiralis)
Disseminated strongyloidiasis symptoms
Lung: ARDS Cough, SOB, wheeze, pulmonary haemorrhage, ARDS
Intestine: Ulceration with bacterial translocation and GN bacteraemias, small bowel obstruction, chronic diarrhoea
Nephrotic syndrome
Larva currens STRAIGHT LINEAR RASH
Strongyloidiasis - diagnostics
Diagnosis: Stool OCP
Sputum for larvae in disseminated disease
Eosinophilia
Serology (in returning travellers, not those from endemic setting)
Strongyloides treatment
- Ivermectin
- Albendazole
Trichuris - clinical features
Chronic trichuris colitis
Gut wall odoema + haemorrhage + rectal prolapse
Trichuris - microscopic features
50-55 microns
Tea tray
Trichuris - treatment
Benzimidazoles
Ascaris lymbricoides - clinical features
Migrates to lung so causes Loeffler’s
GI: intestinal obstruction, biliary obstruction, hepatic abscess
malnutrition
Cestodes - definition
Ribbon like flatworms with segments (proglottids) and a head (scolex) with suckers that attach to the intestinal wall
Taenia saginata - transmission and clinical syndrome
Beef tapeworm
Humans eat contaminated beef, adult worm evolves in the gut and poo out the eggs
Intra-abdominal symptoms, may have the worms around the anus
Taenia saginata - microscopic findings
4 suckers, no hooks
Egg looks like a bike wheel, just over 30 microns
Cystercicosis - organism
Taenia solium
Cystercicosis life cycle
Humans eat pig meat containing cysts or may eat the eggs directly from infected human poo
Taenia solium- clinical presentation
Intestinal infection from eating the adult worm is often mild (i.e. pig meat)
But tissue infection with the larval form from eating eggs (i.e. cystercisosis) can be really severe with seizures secondary to neurocystercicosis
Taenia solium
Differentiate from taenia saginata because of presence of hooks
Diphyllobothrium - life cycle
Copepods eaten by freshwater fish eaten by human.
Develops into an adult in small intestine
Proglottids release the immature eggs which pass into the faeces and back into the water supply
Coracidia hatch from the egg and are eaten by crustaceans
Diphyllobothrium clinical features
GI disturbance
Anaemia (B12 deficiency)
Diphyllobothrium microscopic features
Oval with an operculum, measuring just over 60 microns
Echinococcus granulosus
Dogs are the definitive host
Humans are accidental intermediate hosts by accidentally eating the eggs
No adult worms in the body
Echinococcus granulosus - clinical features
No adult worms in the body
Hydatid diseases
Liver/lung cysts
Anaphylaxis secondary to rupture of these cysts
Echinococcus multilocularis - disease
Alveolar echinococcus
Echinococcus granulosus - disease
Cystic echinococcosis
Echinococcus multilocularis - transmission
From eating eggs in fox poo
Echinococcus multilocularis - clinical features
Slow growing hydratid disease - more like a tumour
Intermediate host
The host harboring the larval stages
Definitive host
Host harbours the sexually mature adult worms
Enterobius vermicularis - life cycle and clinical features
Pinworm i.e. itchy bottom in children
Adults live in the intestine, mature in 2-6 weeks and eggs are laid on the perianal skin
Can cause reinfection from scratching bottom and oral ingestion (i.e. does not need soil to mature)
Enterobius vemicularis - treatment
Mebendazole - treat twice and the entire family. Prevent with hot wash of clothes/linens
Enterobius vemicularis - microscopic features
Egg is 50-60 microns
Looks like a D shape with a flatter edge (Think what comes before E - Denterobius)
Diagnosis from tape test
Trichuris trichiura - geographical distrubution and brief life cycle points
Seen in the tropics
Eating embryonated eggs from contaminated soil or foods
No migration
Need the soil to mature
Trichuris trichiuria - clinical features
Asymptomatic to colitis
Increased risk of bacterial invasion/invasion by entamoeba histolytica/disbar
Anaemia and malnutrition, especially in children
Cestode with >15 uterine branches on microscopy of gravid proglottids
Taenia saginata
Cestode with < 10 uterine brances on the gravid proglottid
Taenia soium
Life cycle of taenia saginata (beef tapeworm) and taenia solium (pork tapeworm)
- Infected meat which is raw/undercooked is eaten by the human
- Cysts develop into adult worms in the small intestine
- Eggs passed by humans in the stool
- If taenia solium eggs are swallowed by humans then this can cause neurocysticercosis
- Or the eggs are ingested by the pigs, which turn into cysts in the muscle
Scolex with 4 suckers but no hooks
Taenia saginata
Scolex with 4 suckers and hooks
Taenia solium
Echinococcus granulosus - organism, clinical syndrome
AKA Cystic echinococcus
Larval form of the dog tapeworm
Causes hydatid disease - well defined fluid filled cysts, mostly in the lung and liver
Diagnosis - imaging, serology
Echinococcus granulosus (cystic echinococcosis)- treatment
< 5cm and no solid or daughter cysts: albendazole alone (+ repeat scan at 6-12 months)
> 5cm and contains solid areas or daughter cysts – percutaneous + albendazole
Complex - i.e. invading other structures, lung cysts (usually rupture with albendazole) and larger cysts need surgical management
Key thing is to prevent rupture and avoid disseminated disease
Watch and wait if non-viable cysts (CE4/5) or if unclear diagnosis/lack of resources/poor candidate etc
Echinococcus multilocularis - key facts
Alveolar echinococcosis
Foxes
Primarily infects the liver but can metastasise elsewhere
Diagnosis - serology, imaging, biopsy if unable to exclude malignancy
Echinococcus multilocularis (Alveolar echinococcosis) - management
Radical surgery with albendazole
Palliative surgery with lifelong albendazole
Hymenolepis nana - microscopic features
Fried egg, 40 x 60
Diphyllobothrium - microscopic appearance and key facts
Eating undercooked fish
Operculum present
Causes B12 deficiency
Paragonimus spp - Transmission risks
Asia
Undercooked crustaceans
Paragonimus - symptoms
Affects lungs - may be mistaken for TB
Ectopic spread to SC tissue, brain
Liver fluke - species and transmission risks
Clonorchis sinensis (SE Asia)
Opisthorcis (China, Russia)
Eating undercooked fish
Liver fluke clinical presentation
Goes to bile ducts
AcuteL abdo pain, jaundice, diarrhoea
Chronic: increased risk cholangiocarcinoma
Fasciola hepatica/buski - transmission risks
Eating waterplants or vegetables
Fasciola hepatica seen worldwide, connections with livestock
Faciola buski seen in SE Asia
Loa loa - pathogen
Filaria of Loa loa (with the nuclei going lower and lower in the sheath to the end of the tail)
Loa loa - vector
Chyrsops silacea (deer flies)
Loa loa - epidemiology
Forest and adjacent savannah regions of central africa
Loa loa - Clinical symptoms and signs
Eye worm migration
Calabar swelling
Dermal rash, arthralgia, myalgia, headache
Rare: encephalitis, Endomyocardial fibrosis, renal, pulmonary
Loa loa - diagnostics
Adult - clinical
MF - microscopy, PCR, LoaScope
Serology in returning travellers only
Loa loa - treatment
DEC/albendazole but avoid in high microfalarial loads
Plasmapharesis an option to bring down the load prior to treatment (in high resource settings)
Loa loa - prevention
Clothes, repellents
High risk travellers - weekly DEC
Lymphatic filariasis - pathogens
Wucheria bancrofti
Brugia malayi
Lymphatic filariasis - epidemiology
Wucheria bancrofti - more in sub-saharan africa
Brugia malayi - India, SE Asia
Lymphatic filariasis life cycle
- Mosquito bites human and deposits L3 larvae which enter the lymphatics
- They migrate through lymphatics and mature to L4 and turn into adult worms in 6-12 months
- Adults can stay in the lymphatics 10-14 years
- Adult female words release Mf whic re-enter the blood stream (nocturnally) - ready for the mosquito to take it up again
- Develops in the midgut and migrate to thoracic muscles
Lymphatic filariasis - clinical presentation
Lymphatic obstruction –> inflammation –> secondary bacterial infections –> lymphodoema
Stage 0 - no lymphoedema
Stage 1 - mild, may be relieved with elevation
Stage 2 - moderate, irreversible changes with minimal skin changes
Stage 3 - severe with skin changes like large knobs, sclerosis, discolouration, mossy lesions
Lymphatic filariasis - diagnostics
Blood smears
Circulating filarial antigen (CFA)
US to detect adult worm nexts in the lymphatic system (can be used pre and post treatment to assess whether its been cured
Lymphatic filariasis - management
Lymphoedema care - hygiene, elevation, emollients, compression bandages
Treat secondary infections
Doxycycline 4-6 weeks - Wolbachia
Hydrocele surgery
Lymphatic filariasis MDA
Africa - Albendazole + ivermectin
Asia and Americas - Albendazole + DEC
Triple therapy in areas without co-endemic loa loa/oncho
In what situations would you avoid DEC in MDA?
Onchocerciasis endemic area (also loa loa at high microfilarial loads)
In what situations would you avoid ivermectin in MDA?
Loa loa endemic area
It’s a cyst and it measures 7-10 microns? Tell me about the three possibilities….
Lemon - chilomastix mesnili
Ring and dot nucleus (1-4) - Entamoeba hartmani
3 winking nuclei - Endolimax nana
The cyst is between 9-12 microns and has a vacuole, what is it?
Iodamoeba butschili
It’s a cyst between 10-15 microns with 2-4 ring and dot nuclei
Entamobe histolytica/disbar
It’s a cyst 15-30 microns with 1-8 ring and dot nuclei
Entamoeba coli
It’s a cyst with a thick shiny cell wall and two sporozoites inside
Cyclospora cayetanesis
It’s a yellow egg in the stool, with striated edges, what’s the species and how big should it be?
Taenia spp
30 microns
It’s an egg in the stool, around 30-40 microns and looks a bit like a fried egg, what is it?
Hymenolepis nana
It’s an egg in the stool that measures around 50 microns and looks like a D shape, what is it?
Enterobius vermicularis
It’s an egg in the stool, around 60 microns. What are the four possibilities?
Ascaris lumbricoides - knobbly edges
Hookworm - thin wall like a pencil
Diphyllobothrium latum - operculum
Hymenolepis diminuta - fried egg
It’s a massive egg around 150 microns. What are the four possibilities?
Schistosoma haematobium - spine pointing down
Schistosoma mansoni - spine to the side (remember flame cell can be seen in the liver prep)
Fasciola hepatica/buski - big old oval with an operculum
It’s an egg around 75-80 microns. What are the three possibilities?
Paragonimus westermani - operculum, thicker wall
Ascaris lumbricoides (infertile) - knobbly
Schistosoma japonicum- spine often not visible
What are the two types of intestinal hookworm in humans that I need to know?
Ancylostoma duodenale
Necator americanus
What are some of the animal species of hookworm?
Ancyclostoma braziliense (walking barefoot on the beach)
Anyclostoma caninum
Ancyclostoma ceylanicum
Hookworm summary
Nematodes (round worms)
Tiny adults with smooth eggs
Faecal to soil to skin transmission plus lung migration
Clinical features include Loeffler’s, GI upset and iron deficiency anameia
Treat with ivermectin/albendazole
Ascaris lumbricoides summary
Like earthworms as adults
Soil to mouth transmission
Found in the tropics
Clinical: Loefflers, GI upset, bowel obstruction
Mx: albendazole
Strongyloides autoinfection mechanisms
Internal:
Some of the L1 larvae mature to L3 within the intestine, penetrate the wall and then migrate to the lungs, starting the process again where eggs can be produced by asexual reproduction
External: some of the L1 larvae penetrate the perianal skin leading to reinfection
Trichuris summary
Nematodes
Soil to mouth transmission
Tropical infection especially in children leading to dysentry and rectal prolapse
Eggs only in the lumen
Mx albendazole
Enterobius vermicularis summary
Pinworm
Itchy anus in children (sellotape test)
Has lateral alae
Faecal oral route
Capillaria philippinensis summary
SE Asia, Japan, Cuba
Ingestion of raw dish
Diarrhoeam abdo pain, weight loss
Mx abendazole
Egg is 40 x 20 microns and looks a bit like trichuris egg but more oval
Cyclospora cayetanensis
8-10 microns
Intermittently acid fast
Co-trimoxazole
Cryptosporidium - microscopy and treatment
4.5 - 5.5 micons (smaller than cyclospora) and bright pink
Nitazoxanide and ART in HIV
Neurocysticercosis - transmission
Ingestion of the T solium eggs (through contaminated water with faeces from an infected individual) unlike eating undercooked pork which contains the cysts
Neurocysticercosis - treatment
Praziquentel but need to consider risk of inflammation/stroke and raised intracranial pressure
Neurocysticercosis - clinical features
Intraparenchymal - seizures/headache due to cysts within the brain tissue
Extraparenchymal -
Subarachnoid, intraventricular 0- headache, cranial nerve palsies, hydrocephalus
Spinal - cysts in the spinal subarachnoid space
Ocular - cysts in the retina
Muscular - calcified nodules
Baylisascaris summary
Roundworm infection linked to old raccoon poo (>2 weeks)
North America, Europe and Japan
Neurological, ocular and visceral larva migrans
Treatment is photocoagulation, albendazole and steroids for neurological disease
Diffuse unilateral subretinal neuroretinitis differentials
Toxoplasmosis
Histoplasmosis
Optic neuritis
Nematodes like - Baylisascaris, Toxocara canis, ancylostoma caninum, gnathostomiasis, strongyloides
Fever, urticaria, dry cough and lung nodules 2-3 weeks after swimming in fresh water
Acute katayama syndrome (schistosomiasis)
Note eggs take up to 3 months to appear in the stool
Differentials for eosinophilia
Infectious (tissue invasive helminths)
Connective tissue diseases
Allergy
Drug induced
Leukaemia/lymphoma
Paraneoplastic
African trypanosomasis organisms, vector, treatment
Trypanosoma brucei gambiense and rhodesiense
Tse tse fly
Fexinidazole (updated 2024 guidelines, was suramin) - for all stages
African trypanosomiasis - acute, rapid progression over 1-4 weeks with a chancre at the bite site - which species?
T b rhodesiense
African trypanosomiasis - chronic, slow progression which can take months to years. Enlarged lymph nodes, mild fever and headache - which species?
T b gambiense
African trypanosomiasis investigations
- Microscopy (blood smear)
- LP
- Card agglutination test for trypanosomiasis (CATT) for T gambiense ONLY
- Moecular approaches
Schistosoma mansoni long term complications
Portal hypertension - hepatosplenomegaly, oesophageal varcies
Note would not present with decompensated liver disease though
Schistosoma haematobium - long term complications
Haematuria
SCC bladder
Echinococcus granulosum - complications
i.e. hydatid cyst
Liver + lung primarily
Fistulas leading to biliary/bronchial obstruction
Superadded bacterial infection
Cyst rupture leading to anaphylaxis
Compression of surrounding structures
Giardiasis treatment
Tinidazole or metronidazole
What are the ectopic features of schistosomiasis?
- Pulmonary
- Spinal
- Cerebral
- Genital
- Cutaneous
What are the most common causes of eosinophilic meningitis?
- Angiostrongylus cantonensis
- Gnathostoma spinigerum
