Hypobiosis/Arrested larval development/Inhibited larval development

Hypobiosis/Arrested larval development/Inhibited larval development:

It is an interruption in development of nematode larvae within the host occurs seasonally, usually at the time when conditions are not favorable to the development and survival of the free living stages.

            Examples:

Haemonchus & ostertagia infection in ruminants –at early L₄ stage.

Hyostrongylus rubidus in pigs

Trichostrongylus sp in horses – at L₃ stages.

The inhibited or dormant larvae do not move, feed & don’t void from the body. their metabolism at the cellular level is reduced but not stops completely. The unfavorable conditions are -

Ecological factors:

• cold weather(Autumn in temperate region )
• lack of moisture (in dry ,hot areas)
• Lack of oxygen etc.

Endogenous factor of host origin:

• Immunity
• Age  
• Ingestion of large number of infective larvae.
• A sizable pre existing adult worm burden

The phenomenon has important epidemiological implications:

• It occurs survival of the worm species during period of adversity
• It results in increased worm fecundity & contamination of the environment at a time when the condition for survival of larvae become more favorable.
• It may result in clinical outbreak of the disease (type-II bovine Ostertagiosis)
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