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To investigate if tick-borne encephalitis virus (TBEV) is present in mammalian wildlife species or ticks in the Netherlands, serum samples and ticks were tested for TBEV antibodies and TBEV RNA, respectively. Serum samples were collected from wild boar (666), deer (13), fox (399), and rodents (90), and were tested for TBEV antibodies, using ELISA, and SN test or HI test. Over a period of 4 years, a total of 906 ticks was collected from seven regions in the Netherlands. In four different regions, this was done on a monthly basis and during four consecutive summers. All ticks were tested for TBEV RNA by RT-PCR. TBEV antibody was detected by ELISA in two (0.5%) sera of foxes and 49 (7%) sera of wild boar, but not confirmed by HI or SNT. TBEV RNA was not detected in any of 906 ticks. It was concluded that there is no real evidence for a TBEV reservoir in ticks or wildlife in the Netherlands. Vector-Borne Zoonotic Dis. 5, 58–64.

A survey was carried out in The Netherlands to determine the prevalence of benzimidazole resistance in sheep nematodes. It was shown that 47 per cent of the 59 investigated flocks harboured trichostrongylid populations with resistance to benzimidazoles, as demonstrated by an LD50 value of 0·12 μg ml–1thiabendazole or higher in an in vitro egg hatch assay. On these farms Haemonchus contortuswas found to be the dominant species. In two flocks resistant Ostertagiaand, or, Trichostrongylusspecies populations were found. Farms with resistance were revisited to determine the anthelmintic efficacy in vivo by means of treatment and egg count. In only four of the 19 flocks which showed resistance in vitro was an efficacy of less than 95 per cent in vivo achieved. This means that there is a discrepancy between the in vivo and in vitro results. Resistance was found more frequently on pure sheep farms than on mixed farms. It is suggested that mixed farms offer more refuge for susceptible H contortuspopulations.

An in vitro egg development assay was used to test the resistance of eggs from a benzimidazole susceptible and a resistant strain of Haemonchus contortusto four benzimidazoles. Storage of eggs contained in faecal samples at 4°C for four, 24 or 72 hours did not appear to impair the results from the in vitro egg development assay or alter the LD50. Storage for one week, however, proved to be lethal for the eggs. The average LD50 values for thiabendazole, albendazole, mebendazole and cambendazole were 0·06, 0·07, 0·96 and 2·47 ppm for the susceptible strain. For the resistant strain the values averaged 0·26, 0·24, 1·07 and 5·11 ppm.

SummaryThe prevalence of anthelmintic resistance in nematodes of sheep was surveyed in 1994 on 70 farms in the Netherlands. An in vitroegg hatch assay, faecal egg count reduction (FECR) 14 days after treatment, and larval cultures were used as methods of investigation. Oxfendazole was tested on 69, ivermectin on 51, and levamisole on 36 farms. The median effective dose (ED50) of thiabendazole could be determined on 64 farms. On 60 farms (94%) the ED50 value was > 0.12 μg ml‐1, which is indicative of the presence of benzimidazole (BZ) resistance. On two farms egg output was too low to do a FECR test. Based on the results of the FECR test, BZ resistance was present on 56 farms (84%), on 2 farms there was a suspicion of resistance and on 9 farms no resistance could be found. No clear indications were found for the presence of resistance against ivermectin or levamisole.BZ resistance was demonstrated in Haemonchus contortus, Cooperia curticei, Ostertagiaspp. and/or Trichostrongylusspp.. No resistance was observed in species from the genus Nematodirus, Chabertia ovinaand/or Oesophagostomumspp.

SummaryThe prevalence of metazoan parasites in the stomach and small intestine was investigated in 70 horses slaughtered in the period February 1994 ‐ July 1994. Most horses were young (1.5 ‐ 3 years) and in good condition. Trichostrongylus axeiwas the most prevalent parasite species in the stomach (51.4%), followed by Gasterophilus intestinalis(41.4%) and Habronemaspp. (4.3%). In the small intestine, Parascaris equorum(28.6%) and Paranoplocephala mamillana(1.4%) were found. The mean worm burden of T. axeiwas 957 (max. 8502), ofG. intestinalis21 (max. 84), of Habronemaspp. 3 (max. 5), and of P. equorum32 (max. 308). One single specimen of P. mamillanawas seen. All bots of G. intestinaliswere in the third instar stage. No seasonal pattern and no influence of the parasites on the condition of the horses could be observed.

SummaryPopulations of animals which live in the wild are regulated by many biotic and abiotic factors. Parasites are one of the biotic factors. Parasites may influence their hosts in different ways. They may cause the death of the host due to a direct lethal effect or an indirect effect. Direct lethal effects may occur if killing is a part of the life cycle of the parasite or if hosts and parasites have not developed an equilibrium. The introduction of hosts or parasites into a new environment with suitable hosts or parasites is an example. Death by parasitism may also be caused by a combination of the emaciating effects of parasites combined with factors such as bad weather conditions, environmental pollution or human handling. Parasites may also influence the behaviour of their hosts. If the hosts are intermediate hosts in the life cycle of the parasites, the alterations in behaviour may make them an easier prey for their predators, the final hosts. Parasites may also influence the reproductive success of the hosts. In this respect the relationship between the red grouse (Lagopus lagopus scoticus) and the caecal nematode Trichostrongylus tenuishas been well worked out.

The resistance level of Haemonchus contortuswas studied on a farm where benzimidazole resistance had been detected in 1980 and where, since 1982, only levamisole had been used for worm control. Egg development tests gave ld50values of 0·18, 0·19 and 0·21 μg ml−1thiabendazole for samples taken from ewes in 1988 compared with 0·21 μg ml−1in 1981. Studies on sheep experimentally infected with larvae cultured from the faeces of these ewes confirmed the continued resistance of H contortusto benzimidazoles, and demonstrated the absence of benzimidazole resistance in other nematode species together with the susceptibility of all species to levamisole.

SummaryThe prevalence of tapeworm infestations was investigated in 70 horses slaughtered in the period February 1994 ‐ July 1994. Most horses were half‐breed, young (1.5 ‐ 3 years), and in good condition. They were bought for slaughter by dealers on local markets, and their treatment history was therefore unknown.Tapeworm infestations were seen in 16 horses (23%). Fifteen (21%) had an infection with Anoplocephala perfoliata. One horse had a single specimen of Paranoplocephala mamillana. The average number of A. perfoliatawas 45 and the highest number was 508.

Using an in vitro egg development assay with thiabendazole as anthelmintic the LC50 of eggs produced by two sheep infected with either a susceptible or a resistant strain of Haemonchus contortuswas followed during the patent period from 22 days to 77 days after infection. In both sheep the LC50 followed the same pattern. At the start of the patent period the average values for the susceptible and the resistant strain were, respectively, 0·05 and 0·21 μg ml–1thiabendazole, after 40 to 60 days 0·09 and 0·35 μg ml–1, while after 77 days 0·07 and 0·24 μg ml–1were recorded.

Resistance of Cooperia curticeiagainst fenbendazole was demonstrated in The Netherlands. Experimental infection of lambs followed by intraruminal injection of 5 mg kg−1showed a 100 per cent survival of the C curticeipopulation. With an in vitro egg development assay lc50 values between 0·23 and 0·38 µg ml−1thiabendazole were found. This is the first record of a Cooperiaspecies resistant against an anthelmintic.