Flashcards in Micromodules: Helminths, Schistosomiasis and Gut Nematodes Deck (27):
Run through Strongyloides steracolis lifecycle from Filariform larvae in the soil, to excretion in the stool
-Filariform larve in the soil penetrate the skin of a human host
-Larvae pass to lungs in circulation
-Larvae migrate to the trachea and pharynx, and are swallowed
-Once they reach the intestine, larvae develop into adults and produce ova.
-Ova hatch to release rhadbitiform larvae
-Rhadbitiform larvae are excreted in the stool
-Rhadbitiform larvae develop into filariform larvae in the soil
How do Strongaloides steracolis cause auto-infection and what are auto-infection symptoms?
The rhabditiform larvae can develop into filiaform larvae in the body and pentrate the mucosa or perianal skin, avoiding excretion and continuing the cycle of infection
Auto-infection is often asymptomatic, though symptoms include diarrhoea, and abdominal pains, with pulmonary symptoms occurring with lung migration
Which population of people are likely to get hyper-infection from S.steracolis?
Immunocompromised patients/those on steroid therapy
Hyper-infection is a potentially fatal disseminated disease
What is the main method of diagnosis of S.steracolis?
Light microscopy; visualisation of rhabditiform larvae in concentrated stools, although serology is also available
What are the two main species of hookworm infecting humans?
Necator americanus and Ancylostoma duedenale.
What is the process of infestation of a human host by Hookworm species?
Infective larvae are found in contaminated soil, and penetrate skin
-These are carried in the blood to the heart and then the lungs
-Coughed up and swallowed
-Larvae make their way to small intestine, where they attach and mature into adults
-Adults shed ova into the lumen
-Ova are passed in faeces/
Describe symptoms of Hookworm infestation
-Major sign is iron deficiency due to GI blood loss
-May impair growth or mental development in children
-Pruritis and rash may occur at site or larval penetration
-Abdominal pain, weight loss and diarrhoea are common
-There may be a cough/wheeze as larvae migrate through lungs
What is the main method of diagnosis for Hookworm?
Visualisation of ova in concentrated stool specimens by light microscopy
Which populations of Australians are most affected by Strongyloides and Hookworm?
Indigenous communities in central and northern territories, in particular where there is poor sanitation leading to contamination of soil
What are the three main groups of Helminths that infect humans?
Cestodes - tapeworms
Nermatodes - roundworms
Trematodes - flukes/flatworms
What is the difference between a definitive host and an intermediate host?
A definitive host is one in which the sexual cycle takes place, while an intermediate host is the host in which larvae develop
What are some examples of Cestodes, and how are they transmitted?
- Taenia solium - pork tapeworm
- Taenia saginata - beef tapeworm
Reservoirs of infection are in mammals like pigs, cattle and dogs. Humans are infected by consumption of cysts in raw/undercooked meat.
Adult worms live in the intestine and shed ova into faeces. Cysts containing larvae can also form in tissues
What are some species of Nematodes?
What are some of the species of Trematodes?
Fasciola hepatica (common liver fluke)
Clonorchis sinensis (chinese liver fluke)
Give brief descriptions of Schistosoma and Liver/lung fluke lifecycles
Schistosomas: larvae penetrate the intact skin, and adult worms develop in venous plexuses of bladder/bowel. Ova penetrate through blood vessels into the bladder or the intestines, and are shed in urine or faeces in into water. Eggs hatch in the water, and larvae penetrate freshwater snails (intermediate host)
Liver/lung flukes: ingestion of cysts in water plants, fresh water dish or crabs, which act as intermediate hosts. Adult worms live in bile ducts or lungs, and Ova are shed into faeces, into water.
How do schistosomas infect human hosts?
Through contact with fresh water; free swimming Schistosomas penetrate skin of persons who come into contact with contaminated water.
Describe the physical orientation of the female and male adult worms
The smaller male sits within the adult females ventral groove
How do eggs from different species of Schistosomas differ?
Whether they have a spine or not, how the spine is oriented (terminal or later) and how big they are
What is Katamaya fever?
A systemic illness that occurs during early adult development and egg production by Schistosomas.
Signs/Symptoms include: high fevers, chills, muscle pain, rash and an enlarged liver/spleen
What are some late clinical features of infection by Schistosomas?
Granuloma formation around eggs
S.haematobium eggs are depositied in bladder, causing haematuria. Chronic infection by this Schistosoma can lead to carcinogenesis of the bladder
Other species deposit eggs in bowel and liver, causing abdominal discomfort, blood in stool, liver fibrosis and postal hypertension
How do you diagnose Schistosomiasis?
Serology - but this doesn't distinguish between current infection and past treated infections
Microscopy - stool examination when infection is suspected, or urine examination for S.haematobium
-Eggs are released intermittently, so repeated examinations may be needed
How do you treat Schistosomiasis?
This treats all of them, and two or three oral doses in a single day cures most cases.
BUT it's only effective against adult worms, so treatment must be delayed until 8 weeks has passed since freshwater exposure
Why is serolgy not used as a 'test of cure' investigation?
It will remain positive following treatment.
It's best to use a follow up examination of stool/urine, 1-2 months post-treatment to suggest a successful cure
What's the annual death rate from Schistosomiasis?
It is a Neglected tropical disease, despite affecting up to 20 million people
What areas to control efforts usually focus on when trying to prevent Schistosomiasis?
1. Community treatment - regular treatment of entire populations, or targeted treatment. Burden of infection is highest in children so they are most likely to be targeted
2. Eliminating snail species that maintains the parasite's life cycle
What is the pharmacological treatment for Strongyloides?