Survival of first stage larvae (L1) of Angiostrongylus vasorum under various conditions of temperature and humidity.

This experiment has been conducted to evaluate the viability of Angiostrongylus vasorum L1 under different conditions of temperature and humidity. In order to assess the viability, fox faecal pellets containing first stage larvae (L1) were exposed to relative humidity (RH) 95% and 75%, and to different temperatures (5°C, 18°C) and at fluctuating conditions ranging from -5°C to +5°C. Moreover, larval viability under outdoor conditions in April was also observed. Survival of the larvae was strongly influenced by temperature; however, humidity did not show any significant influence on viability. In controlled condition, 100% of the larvae were found motile and active; whereas, around 14% and 19% of the larvae kept at 5°C remained viable at RH 95% and RH 75%, respectively after 78 h. All of the larvae kept at 18°C died after 66 h. In outdoor condition, larval survivability reduced to 18% after 66 h, and in fluctuation temperature viable larvae were observed in both control and experimental conditions (15%) after 78 h.

Effect of irradiation on the viability of Angiostrongylus cantonensis and A. costaricensis infective larvae.

Infective larvae (third-stage larvae) of both Angiostrongylus cantonensis and A. costaricensis from their snail intermediate host were subjected to either X-ray or gamma-ray irradiation. The viability of the irradiated larvae was assayed by oral inoculation of the larvae into rodents (A. cantonensis in mice and rats, A. costaricensis in mice only). From the results of worm recovery, the minimal dose of irradiation that inhibited the infectivity of the third-stage larvae of A. cantonensis and A. costaricensis was 2 and 4 kGy, respectively.

Motility and drug susceptibility of Angiostrongylus cantonensis developing from gamma-irradiated first-stage larvae.

The effects of neuropharmacological agents on the motility of irradiated and non-irradiated Angiostrongylus cantonensis adult females were studied. GABA induced complete paralysis in non-irradiated and 5,000 R-irradiated worms, but caused only slight paralysis on 10,000 R-irradiated worms. The paralytic effect of GABA was antagonised by picrotoxin. The reason for low susceptibility of heavily irradiated worms to GABA is not known. There was no difference in susceptibility of non-irradiated and irradiated worms to other neuropharmacological agents including eserine, phenylephrine and dibenamine.

Late development and fertility of adult worms derived from gamma-irradiated first-stage larvae of Angiostrongylus cantonensis.

Effects of gamma ray irradiation on the first-stage larvae of Angiostrongylus cantonensis were studied. Compared to the non-treated controls, infection of rats with third-stage larvae which developed from irradiated first-stage larvae resulted in reduced recovery rates of adults. There was also a change in the male-female adult worm ratio and a reduction in larval output per female in relation to increasing irradiation dosage. Morphological changes in the adults were noted.

Effect of UV-irradiation, spleen cells and MLN cells on protective immunity against Angiostrongylus cantonensis infection in mice.

The UV-irradiated larvae of Angiostrongylus cantonensis were used for inducing immunity in mice. A single oral dose of 100 infective UV-irradiated larvae exposed for 5 min or 15 min induced 91% and 97% protection against subsequent infection. Adoptive protection against A. cantonensis could also be transferred by spleen and mesenteric lymph node cells obtained from vaccinated mice.

Infectivity and development of the gamma-irradiated first stage larvae of Angiostrongylus cantonensis.

Effects of gamma-ray irradiation on the first-stage larvae of Angiostrongylus cantonensis were studied. There was a significant reduction in the infectivity of the 10,000 R-irradiated larvae to intermediate host snails compared to other groups. In the final host infection, both the worm populations and worm body length of irradiated groups differed markedly from those of the non-irradiated control.