The major conclusion of this study is that autumn, and to a lesser degree summer, treatment with injectable ivermectin resulted in decreased severity of peritonitis and perihepatitis in reindeer calves due to setariosis. The pathological changes caused by S. tundra have been associated to the decrease of the body condition of slaughter calves . In trial III, a slight benefit of midsummer ivermectin treatment was detected in the highly endemic area of S. tundra. Fat layer was thicker in the ivermectin group and the quality of livers was better, the liver and, especially the liver capsule, being the primary location of changes caused by S. tundra.
Antiparasitic treatment of slaughter calves and its benefits during summer round-ups has been frequently discussed among reindeer herders during the S. tundra outbreak and has been practised in some individual cooperatives. In one earlier study in Finland,  no benefit of this type of treatment to the summer and autumn growth of reindeer calves could be demonstrated. However, in that work the study conditions differed from the present in that there were no observations of S. tundra infection or any associated pathological changes  in the study area.
According to the trial I, autumn antiparasitic treatment of reindeer calves during heavy outbreak, before slaughter season, could improve results, maybe not in weight gain indicators, but by reducing condemnations during meat inspection. However the economical feasibility of treatment at this time can be questioned. Chemical treatment of calves to be selected for slaughter could damage the organic reputation of reindeer meat in foodstuff market . In Finland, only veterinarians are allowed to give ivermectin injections to reindeer which increases the costs of the antiparasitic treatment and adding the costs from extra round-ups, total costs could easily exceed the benefit. Nevertheless, in situations where a heavy outbreak is evident and the reindeer calves' welfare demands, efficient antiparasitic treatment is available and should be used.
Ivermectin injection (200 μg/kg b.w. s.c) proved to be efficient against adult S. tundra nematodes in the abdominal cavities of calves (trial I). It was also efficient against smf in blood circulation, at least on the individual reindeer level. In trial I, there were no live S. tundra nematodes in the abdominal cavity in the treated group. In addition, healing processes and the organization of the inflammatory changes in the abdominal cavity had clearly started one month following the ivermectin treatment. This demonstrates that the peritonitis is associated with living S. tundra nematodes in abdominal cavity as earlier presented . The results also show that routine antiparasitic treatment, especially of calves which are left alive for breeding purposes, is well funded.
In trial I, none of the six calves slaughtered 30 days after ivermectin treatment had live smf in the blood circulation, but three of the five calves slaughtered 57 days after treatment had. In trial II, the proportion of smf positives was 4% of the treated reindeer 44 days after ivermectin injections. The results may indicate partial efficiency of ivermectin against migrating larvae , which might have subsequently matured and started to produce smf. However, this part of S. tundra nematode's life cycle is still poorly understood. The possible bias because of reinfection was not possible because of the luck of insects and S. tundra nematodes' 3 to 4 month's pre-patent time . The variable efficiency of ivermectin against the developing stages of filarioidea nematodes has been shown earlier by . Another possibility is that the larval output was temporarily suppressed by ivermectin as shown in other filarioidea species reviewed by . Ivermectin is also commonly used in the control of human filariosis because of its potent effect on mf . Although there is currently no formal evidence for the development of resistance to any drug used against filariasis several cases of 'non- or poor responsiveness' to treatment of onchocerciasis with ivermectin have been reported . This is also important to keep in mind, especially after decades of mass ivermectin treatment of Finnish reindeer population . Overall, the results obtained from our trials were comparable to earlier reports in which the variable efficiency of ivermectin against Setaria spp. infection has been demonstrated in domestic animals. These results demonstrate that the efficiency of ivermectin (200 μg/kg b.w.) against the circulating Setaria microfilariae (smf) is better, varying from 88 to 100%, than against the adult worms (67–84%) [21–26].
Prevention of S. tundra transmission by the insecticide and mosquito repellent, deltamethrin, was not successful. It is possible that the effect of pour-on deltamethrin solution against mosquitoes does not last very long in nature in the occasionally rainy conditions in Finland. In addition, the relatively slight preventive effects of both ivermectin and deltamethrin treatment during mid summer round-ups may be due to the transmission dynamics of S. tundra. The development of smf after the mosquito's blood meal to the infective stage is temperature dependent and lasts at least about two weeks [2, 27–30]. This is congruent to the conclusion  that the most active transmission time of S. tundra is between early July and late August. In midsummer, the mass appearance of mosquitoes has just started and by the time when these intermediate hosts become active vectors the plasma concentration of ivermectin has decreased in reindeer  and deltamethrin is diluted. A more efficient way to prevent transmission in mid summer could be the medication of the older animals in the herd, the reservoir of S. tundra especially when the role of wild cervids as reservoirs for S. tundra is in North Finland insignificant . A limitation to this would be the fact that handling is difficult at that period because of the fragile growing velvet antlers of adult reindeer.
It has been proposed  that reindeer calves pick up gastro-intestinal parasite larvae at an early age in late June or early July. However the infection pressure of the parasites is likely strong also later in the summer, which may explain why there were no distinguishable differences in the prevalence or intensity of other ecto- and endoparasite infections between groups in this study. Another explanation, parasite resistance to ivermectin because of widespread and long standing use of ivermectin, demands further research efforts.
According to the questionnaire antiparasitic treatment with ivermectin was relatively intensive in 2002–2004: about 80% of Finnish reindeer got medication. The use of equine ivermectin paste administered per os was common in southern areas. In the area 1 in 2002, just before the outbreak, 24% of reindeer got paste and only 52% got ivermectin administered by injection. During the course of the outbreak, the proportion of injection increased to 68%. This was mainly due to advice given by the Reindeer Herders' Association and by the reindeer health care programme by Finnish Food Safety Authority Evira. The use of oral administration of ivermectin was not recommended because of the weaker efficiency against gastrointestinal nematodes [32, 33], lower achieved plasma concentrations and the danger of emerging drug resistance . It is unclear if the high proportion of reindeer treated by oral administration of ivermectin is connected with the genesis of the outbreak in this area  where the reindeer density is only about half of the densities in the two northern areas (Table 3). Although mf are usually very susceptible to ivermectin, the adult filarioids are not . It is reasonable to think that the lower ivermectin concentration in reindeer achieved by oral administration has lesser efficiency against adult S. tundra nematodes. In the area 3, the treatment with ivermectin injection was intensive during the study period, 87% of reindeer in 2003 and 90% in 2004, which is almost as high as it could ever realistically get in reindeer management. Even then, the outbreak emerged to the area; 63% of viscera condemned in 2005 and the prevalence of smf positive reindeer calves increased from 16% in 2004 to 60% in 2006. Simultaneously, the outbreak settled down in the southern area [1, 9].
The results obtained from this study give additional evidence of the pathogenity of S. tundra to reindeer and suggest that a heavy infection rate may have detrimental effects on Rangifer populations. In addition, recent studies give rise to the hypothesis that the currently high prevalence of filarioid nematodes in cervids [1, 9] and in cattle  in Finland may be associated with the ongoing climate change.
Observations made in this study support the conclusions of the very efficient transmission and potent vectors of S. tundra nematodes as well as deductions about the impact of growing immunity against S. tundra  in regulating the infection degree and dynamics in reindeer populations. This was also seen earlier in an experiment when hinds in the zoo with very low smf value managed to transfer the infection to their offspring and all infected calves cleared the infection within two years . It is likely that on the population level, these factors are more important than the field efficiency of ivermectin in regulating S. tundra infection transmission to the next generation. Therefore, it is essential to gain knowledge of the basic biology and dynamics as well as preventive measures, including drug resistance studies, against these nematodes, there is growing interest in the subarctic areas.