An epidemiological study of Fasciola hepatica in The Netherlands.

Transmission of F. hepatica under natural conditions was analysed in a three year programme. The variables used were the indirect haemagglutination (IHA) technique, worm establishment in tracer lambs and the population dynamics, infection rate and shedding pattern of Lymnaea truncatula. It is concluded that fluke eggs, infected snails and metacercariae on herbage can survive the winter in the Netherlands. Metacercarial availability was positively correlated to the amount of rainfall in the grazing period. The role developed eggs that survive the winter is important, because this results in earlier infections in the herd. The use of the serological diagnosis method IHA is important to detect F. hepatica infection in an early stage. Use of cellophane paper on floats is a useful method for determining the shedding pattern of cercariae from L. truncatula. It is concluded that collection of metacercariae on cellophane floats, inventarization of L. truncatula and its infection level are useful tools for the prediction of liverfluke infections.

[Early diagnosis of liver fluke infection in sheep]. / Vroegdiagnostiek van leverbot-infectie bij het schaap.

The sera and livers of slaughtered lambs were studied in October 1987 in order to achieve a suitable interpretation of the indirect haemagglutination assay (IHA) in the diagnosis of fascioliasis in flocks. In view of these studies, it is concluded that the IHA is useful in the early diagnosis of liver fluke infection in lambs. It is recommended to take samples from at least five lambs in each flock. An interpretation model is provided.

Livestock mortality in Afghanistan in districts with and without a veterinary programme.

This paper reports on livestock mortality in Afghanistan where a war has been going on for more than a decade, with complete disruption of the veterinary field services. The study attempted to measure the impact of a veterinary field programme carried out mainly by paravets. The study also provides valuable data on the impact of diseases in the absence of any veterinary intervention. The veterinary programme, implemented by a Dutch non-governmental organisation (NGO) for approximately 3 years, consisted essentially of vaccination against major infectious diseases and administration of anthelmintic drugs for nematodes and liver flukes. Veterinary personnel were also involved in curative treatments. Livestock mortality figures were collected by questionnaire over a period of 2 years from more than 700 farmers in randomly selected villages in 4 covered districts with a veterinary programme and 4 control districts without a veterinary programme. The average annual mortality rates for calves, lambs and kids respectively were 16.2%, 17.3% and 19.1% in the covered areas, against 21.5%, 25.2% and 24.6% in the control areas. Adult mortality figures were 3.8%, 7.4% and 5.4% in the covered areas, against 5.3%, 13.6% and 15.6% in the control areas for cattle, sheep and goats respectively. The survey indicated significant differences (P < 0.01 in cattle, P < 0.001 in small ruminants) in livestock mortality between the control and covered areas and it is concluded that these differences were attributable to the presence or absence of the animal health programme.

Further observations on the impact of a veterinary programme in Afghanistan on seasonal livestock mortality.

This paper reports further results of a two year livestock mortality survey in Afghanistan, where a war of more than a decade had completely disrupted the veterinary field services. A questionnaire-based survey to measure the impact of a veterinary field programme indicated that average annual mortality in cattle, sheep, and goats was substantially lower in districts that received veterinary services (covered districts) than in districts without any veterinary services (control districts). The impact of the programme varies according to the season and the age group of the animals involved. The programme lacked impact in winter, in particular in adult small ruminants. The highest impact was noted in the spring and autumn for adult goats, and summer and autumn for adult sheep. The impact of the programme was also limited (in small ruminants even completely absent) during the suckling period in young animals. The highest impact was noted in the post-weaning period in small ruminants, when approximately four times more lambs and kids died in the control districts than in the covered districts. It was concluded that the major impact of the veterinary programme was achieved when animals are in contact with other flocks during grazing seasons, when parasitic and infectious diseases are present and against which the veterinary programme is directed. Additional inputs-including extension activities-are therefore required to improve the effect of the programme in the winter and in the neonatal period.

Neural coding in antennal olfactory cells of tsetse flies (Glossina spp.).

Spike trains from individual antennal olfactory cells of tsetse flies (Glossina spp.) obtained during steady-state conditions (spontaneous as well as during stimulation with 1-octen-3-ol) and dynamic stimulation with repetitive pulses of 1-octen-3-ol were investigated by studying the spike frequency and the temporal structure of the trains. In general, stimulation changes the intensity of the spike activity but leaves the underlying stochastic structure unaffected. This structure turns out to be a renewal process. The only independently varying parameter in this process is the mean interspike interval length, suggesting that olfactory cells of tsetse flies may transmit information via a frequency coding. In spike records with high firing rates, however, the stationary records had significant negative first-order serial correlation coefficients and were non-renewal. Some cells in this study were capable of precisely encoding the onset of the odour pulses at frequencies up to at least 3 Hz. Cells with a rapid return to pre-stimulus activity at the end of stimulation responded more adequately to pulsed stimuli than cells with a long increased spike frequency. While short-firing cells process information via a frequency code, long-firing cells responded with two distinctive phases: a phasic, non-renewal response and a tonic, renewal response which may function as a memory of previous stimulations.