Arrested development of Ostertagia ostertagi: effect of the exposure of infective larvae to natural spring conditions of the Humid Pampa (Argentina)

The efficacy of an isolate of the nematophagous fungus Duddingtonia flagrans against gastrointestinal nematodes of cattle was examined at 2 dose levels on 2 permanent pastures, with high and low stocking rates, respectively. Thirty calves, experimentally infected with Ostertagia ostertagi, were divided into 3 comparable groups and allocated to 3 similar paddocks in each of the 2 trials. Two of the 3 groups received fungal material once per day during the initial 2 months, either at high dose (106 fungal spores/kg body weight) or low dose (5×105 or 2·5×105 fungal spores/kg body weight). The third group remained as an untreated control group. Faecal, blood, and herbage samples were collected and animals were weighed every month from May to September. The pasture grazed at a high stocking rate had a large number of overwintering infective larvae, while the pasture grazed at a low stocking rate had a low overwintering herbage larval infectivity. The results showed that, at a high stocking rate, the recovery of infective larvae on pasture was diminished and calves were prevented from clinical ostertagiosis by using the D. flagrans Troll A-isolate. At low stocking rate, the parasite burden seemed not to be very heavy, and a conclusive effect of the fungi at the dose-level used could not be detected.

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In vitro Cultivation of Ostertagia ostertagi, the Medium Stomach Worm of Cattle. I. Development from Infective Larvae to Egg-Laying Adults

Journal of Parasitology ◽

10.2307/3280016 ◽

1977 ◽

Vol 63 (3) ◽

pp. 520 ◽

Cited By ~ 12

Author(s):

Frank W. Douvres ◽

George M. Malakatis

Keyword(s):

Egg Laying ◽

In Vitro Cultivation ◽

Ostertagia Ostertagi ◽

Infective Larvae

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Inhibited development in Ostertagia ostertagi infections – a diapause phenomenon in a nematode

Parasitology ◽

10.1017/s0031182000048009 ◽

1974 ◽

Vol 69 (2) ◽

pp. 161-174 ◽

Cited By ~ 112

Author(s):

J. Armour ◽

R. G. Bruce

Keyword(s):

Oral Administration ◽

Worm Burden ◽

Cold Climate ◽

Environmental Stimulus ◽

Free Living ◽

Ostertagia Ostertagi ◽

Infective Larvae ◽

Fourth Larval Stage ◽

Autumn And Winter ◽

Fixed Period

Experiments are described which show that in a recently isolated field strain of the cattle nematode, Ostertagia ostertagi, the primary stimulus to the induction of inhibited development at the early fourth larval stage (EL4) in the host is chilling of the infective larvae (L3). Thus exposure of L3 to a temperature of 4 °C for 8 weeks prior to their oral administration to calves resulted in a mean of 66% of the established worm burden becoming inhibited at the EL4 stage. This provides an explanation for the seasonal occurrence in Britain of inhibited EL4 stages of O. ostertagi in cattle during the cold climate of late autumn and winter.If the L3 stages were exposed to chilling for a prolonged period (> 19 weeks), prior to infection of calves, then the prevalence of inhibited EL4 stages amongst the worms established declined. After 33 weeks chilling the worm population consisted almost entirely of adults and only 2% inhibited EL4 stages. This suggested that a selective mortality of inhibition prone L3 was taking place and explained why under natural grazing conditions inhibition prone L3 were not available on the pasture in spring.The duration of inhibition at the EL4 stage in calves infected with chilled L3 was consistently between 16 and 18 weeks and maturation of the majority of the inhibited larvae occurred spontaneously after such a period and irrespective of season. This period is equivalent to the duration of a normal winter in Britain when conditions unsuitable for the free living development of O. ostertagi larvae prevail.The induction of inhibition by the environmental stimulus of chilling, the fixed period for the duration of inhibition within the host and the spontaneous maturation of the inhibited larvae are characteristic of a true diapause.

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