Threadworm

(Strongyloides species)

Strongyloides papillosus occurs in the small intestine of cattle, sheep, goats and other ruminants all over the world. Threadworms of a different species occur in other animals and man. Each species is host-specific i.e. it only develops in its preferred host.

Infection is most often associated with young animals managed at high stocking rates under moist unhygienic conditions in warm climates. Calves as young as 3-5 months of age are affected and a strong host resistance develops by about 8 months of age. Young dairy calves in coastal eastern Australia, and buffalo in the Northern Territory are commonly infected but numbers of invading parasites are usually low.

Figure 1. Eggs of the threadworm, Strongyloides papillosus. Image courtesy of Dr Mani Lejeune, Cornell University Animal Health Diagnostic Centre.

The adult worms are thin and thread-like, 3.5–6 mm long. Only parthenogenetic female worms are present in cattle.

Further ecological information on worms and their control:

  • Roundworm life cycle and life stages
  • The life cycle is complex with both parasitic and non-parasitic life cycles. Parthenogenetic female worms buried in the mucosa of the small intestine of cattle lay small eggs containing a first stage larvae. Eggs hatch rapidly and develop directly into infective larvae or after four moults, into free-living adults. Infective larvae penetrate the skin of cattle near the hooves, and move to the lungs via the circulation where they migrate through the alveoli, up the trachea and are swallowed.
  • Free living adults in the soil undergo a number of non-parasitic life cycles before once again producing larvae infective to cattle.
  • Oral infection of cattle may also occur. Infection of the calf also occurs through milk during suckling. The pre-patent period is 10-12 days.
  • Climate factors contributing to paddock contamination with worms
  • Pasture management to reduce exposure to worms
  • Cost of roundworms

Location in cattle

Threadworm inhabits the small intestine of young cattle.

Signs

Infection is common in very young animals. Disease is only seen in very heavy infestations. Depression, weight-loss, harsh coat, diarrhoea, and inflammation between the toes are typical. Repeated skin penetration can result in oedema, serum exudation and scab formation at the site of entry. Death can occur in calves shortly after skin penetration.

Signs of worms

Diagnosis

The characteristic eggs are found on a worm egg count (WEC) when analysing dung samples for other roundworm eggs.

Treatment

Broad-spectrum anthelmintics give good control of this worm.