A survey of Plasmodium falciparum infection and clone multiplicity in Ghanaian children was carried out to study the effect of the onset of the malaria transmission season on disease incidence. Fortnightly blood samples were collected from 40 children living in the rural town of Dodowa, between February and August 1998. P. falciparum parasite densities were calculated and PCR genotyping was carried out using the polymorphic MSP-1 and MSP-2 genes as target loci for the estimation of the number of parasite clones in each sample. The average clone number was estimated using maximum likelihood techniques and the minimum number of clones per patient was analysed for the effects of age, sex, season, minimum number of clones per child, level of parasitaemia and parasite genotype. The statistical analysis indicated that the more clones a child carried, the more likely they were to have a clinical malaria episode. This was true after adjusting for age and season effects and for the measured circulating parasitaemia. The probability of clinical disease also increased if the MSP-1 MAD 20 and the MSP-2 FC 27 alleles were present. This longitudinal analysis thus indicates that the probability of a Ghanaian child having a symptomatic malaria episode is positively associated with both increasing numbers and novel types of P. falciparum clones.

Egg production by the freshwater gill monogenean Discocotyle sagittata infecting rainbow trout (Oncorhynchus mykiss) was monitored at 5, 13 and 18°C; eggs were incubated at 6, 10, 13, 15, 16, 18, 22 and 26°C and the hatching times determined. Mean per capita output at 13°C ranged from 0·8 eggs/worm/day (e/w/d) to 18·3 e/w/d for 25 hosts (burdens 1–17 worms/host). Average egg production rates for worms in single burdens varied from 3 e/d to 14·6 e/d at 13°C, mean 7·6 e/d (±0·63) (n=8). Egg production was temperature dependent, increasing from a mean of 1·5 e/w/d at 5°C to 12·0 e/w/d at 18°C. Developmental rate was also temperature dependent: larvae began hatching after 84 days at 6°C, 28 days at 13°C, and 20 days at 18°C. Eggs laid within the same 24 h period hatched over 3–7 days at 13–18°C; this range was extended at decreasing temperatures. Egg viability was generally high: between 13 and 18°C a mean of 92% of larvae successfully emerged. However, viability declined at the highest and lowest temperatures (23% hatching at 6°C, 55% at 8°C and 47% at 26°C). The implications for seasonal parasite transmission are discussed.