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Endoparasites - Strongyloides

Strongyloides papillosus: Intestinal threadworm. Not reported in cattle in NZ but certainly are found in sheep so probably do occur in cattle. Separate species occur in NZ pigs and horses.

General Description: Adults are short and thin, 3.5 to 6mm long and only 0.05 to 0.06mm wide.

Life Cycle: Parthenogenetic female adults in the intestine lay eggs which do not need fertilisation by sperm to develop. Larvae begin to form in them before passing in faeces. On pasture the eggs hatch quickly and larvae moult to become infective third-stage larvae in 24 to 48 hours (homogonic cycle); these infect animals by skin penetration or by ingestion. Strongyloides papillosus can cross the placenta, infecting calves before birth. These nematodes can also pass in colostrum to newborn calves. The circulation then carries the larvae to the lungs. After being coughed up and swallowed, they develop to adults approximately 7 to 9 days after infection. There may be a free-living stage in addition to the parasitic stage (heterogonic cycle).

Location: Small intestine.

Geographical Distribution: Worldwide, especially in warm humid areas.

Significance: Intestinal threadworms are widespread, multiply rapidly, young animals are often infected.

Effect on Host: Infective threadworms penetrate the host´s skin and migrate to the lungs where they damage tissue. Adults inhabit the intestine, causing severe inflammation and bloody diarrhoea. Immunity develops to Strongyloides infections, and young cattle that do not have this immunity may be seriously affected.

Diagnostic Information: Eggs are small and embryonated, already containing larvae when passed in faeces.

Control: Pasture management; drain pastures, keep barns dry. Treat cattle with anthelmintics.

Threadworms   Tissue section showing larva under skin   Consolidation caused by larval migration in lungs

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