There are circa

species of Strongyloides. The human species are

and

They have limited pathology except in

and in

S. stercoralis is the most common and occurs in many

and

regions

S. fuelleborni is much rarer and there appears only to be an

transmission from

of the worms body is ovary. The female is mostly

and sex only occurs

when conditions are stressful. In the Strongyloides lifecycle, the larval progeny can develop into

or

Those that develop into free living larvae then reproduce

to produce larvae that develop into

(indirectly). When these infect a host they develop into

Direct development is known as

development. Whereas indirect development is known as

development. Infective L3s are

and therefore migrate away from the faeces, they are

resistant and can survive for months in a developmentally arrested state until contact with a suitable host.

T. circumcincta is a

parasite. It has a

lifecycle. The

pass in the

the

develop in the

resulting in

sheathed in

The sheep graze on the

The larvae develop into

larvae and

in the

There is variation among sheep in the

of T. circumcincta

Ascaris is a

nematode. It has a

lifestyle. The larger worm is

as larger size = greater

Ascaris infects around

individuals. Particularly in the

Ascaris

is the human species. Ascaris

is the pig species. Are they able to infect host species or are they host specific?

How can you determine the transmission cycle?