Metastrongyloidae

Also known as the 'lungworms', but beware! - not all worms in the lungs are metastrongyloids!

Aeurostrongylus abstrusus - Courtesy of the Laboratory of Parasitology, University of Pennsylvania School of Veterinary Medicine

Metastrongylus larva from pig faeces - Joaquim Castellà Veterinary Parasitology Universitat Autònoma de Barcelona

Metastrongylus from pig faeces - Joaquim Castellà Veterinary Parasitology Universitat Autònoma de Barcelona

Dictyocaulus arnfieldi from horse faeces - Joaquim Castellà Veterinary Parasitology Universitat Autònoma de Barcelona

General Appearance

Bursate
Typically, look like pieces of string (some, though, are very small)
Each species has a predilection site at some level in the respiratory tract (e.g. trachea and bronchi, bronchioles, alveolae and parenchyma) or associated blood vessels

General Life-Cycle

The typical life-cycle is indirect, with a molluscan intermediate host
There are some exceptions (e.g. Metastrongylus in pigs, which use earthworms as intermediate hosts, and Filaroides in dogs, which has a direct life-cycle)
Adult female lungworms → eggs → wafted up trachea by epithelial cilia → throat → swallowed → pass through alimentary tract
Eggs typically hatch en route → L1 in faeces
L1 has a wavy tail and some species also have a sub-terminal peg
L1 eaten by mollusc intermediate host → infective L3
If small mammals or birds eat the mollusc intermediate host, the L3 of some species (e.g. Aelurostrongylus, the cat lungworm) invade the tissues and utilise the animal as a paratenic host
The final host is infected by ingesting an intermediate or paratenic host carrying the L3
The L3 migrate from the intestine → mesenteric lymph nodes → blood → lungs
Prepatent period varies between species

NOTE: the most pathogenic worms in the lungs of ruminants and equines belong to the genus Dictyocaulus. These look like typical metastrongyloid lungworms, but molecular studies have confirmed that they are related to the Trichostrongyloidea (a case of convergent evolution). This explains why their life cycle is so different from the others.

Angiostrongylidae

Filaroides

Protostrongylus spp. can block bronchioles in sheep

Angiostrongylus vasorum live in pulmonary arteries of dogs

Aelurostrongylus abstrussus in lung parenchyma and small bronchioles of cats

Filaroides osleri causes infection in trachea of dogs

Metastrongylus spp. in bronchi of pigs

Muellerius capillaris common parasite of sheep and goats in respiratory infections

Crenosoma vulpis lungworm of dogs and foxes