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Providing evidence to improve practice

Action: Use drugs to treat parasites Terrestrial Mammal Conservation

Key messages

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  • Seven studies evaluated the effects on mammals of using drugs to treat parasites. Three studies were in the USA, two were in Spain, one was in Germany and one was in Croatia.

COMMUNITY RESPONSE (0 STUDIES)

POPULATION RESPONSE (7 STUDIES)

  • Survival (1 study): A randomized, replicated, controlled study the USA found that medical treatment of Rocky Mountain bighorn sheep against lungworm did not increase lamb survival.
  • Condition (6 studies): Three of four before-and-after studies (one controlled), in Germany, the USA and Croatia, found that after administering drugs to mammals, parasite burdens were reduced in roe deer and in wild boar piglets and numbers of white-tailed deer infected were reduced. A third study found that levels of lungworm larvae in bighorn sheep faeces were reduced one month after drug treatment but not after three to seven months. One of these studies also found that the drug treatment resulted in increased body weight in roe deer fawns. A replicated, controlled, before-and-after study in Spain found that higher doses of ivermectin treated sarcoptic mange in Spanish ibex faster than lower doses, and treatment was more effective in animals with less severe infections. A replicated, before-and-after study in Spain found that after injecting Spanish ibex with ivermectin to treat sarcoptic mange a mange-free herd was established.

BEHAVIOUR (0 STUDIES)

Supporting evidence from individual studies

1 

A before-and-after study in 1979–1986 in a forest area in Middle Rhine, Germany (Düwel 1987) found that supplementing food with a drug to reduce parasitic worms reduced parasite burdens and increased body weights in roe deer Capreolus capreolus. After seven years of treatment, nematode burdens were reduced by 95% in fawns and 99% in adult deer, compared to levels before treatments began. Average weights of fawns killed for venison increased during this time to 9.4 kg, from 4.9 kg prior to treatment with the drug. Following discovery of high nematode burdens and associated mortality in 1979, winter fodder of deer (bran, mill leftovers and maize silage) was supplemented with anthelmintic powder (Fenbendazole, containing 4% Panacur) for seven years in a dose of 5 mg/kg body weight. Parasite burdens were assessed from faecal samples and from 90 carcasses collected before and 57 after treatments.

2 

A replicated, controlled, before-and-after study in 1987–1988 in a state park in South Dakota, USA (Easterly et al. 1992) found that following medical treatment, lungworm larvae levels in bighorn sheep Ovis canadensis faeces reduced over the following month, but not 3–7 months after treatment. In the month following treatment, average concentrations of lungworm larvae in faeces of bighorn sheep treated with one dose (50–250 larvae/g faeces) or two doses of ivermectin (50–300 larvae/g faeces) were lower than in untreated sheep (500–1,400 larvae/g faeces). However, by 3–7 months after treatments, average concentrations of lungworm larvae did not differ significantly between treated (600–1,300 larvae/g faeces) and untreated sheep (300-600 larvae/g faeces). One group of free-ranging female sheep received alfalfa treated with the anti-parasitic drug ivermectin in February 1987 and 1988 (four and six individuals, respectively) and another group received it in both February and March 1987 and January and February 1988 (seven and 14 sheep respectively). Five (1987) and nine (1988) sheep were untreated. Each treatment was administrated over two successive days at a rate of 2 ml ivermectin/sheep, and sheep were pre-baited with untreated alfalfa two weeks prior to each treatment. Parasite counts were made through analysing sheep faeces collected weekly from January to March and June to August in 1987-1988.

3 

A controlled, before-and-after study in 1987–1989 in a grassland wildlife refuge in Texas, USA (Qureshi et al. 1994) found that feeding white-tailed deer Odocoileus virginianus medicated corn reduced trematode Fascioloides magna parasite infection by 63%. Four weeks after treatment with triclabendazole, fewer white-tailed deer were infected with live parasites (2/23) than in baited control (15/24) and unbaited control areas (24/30). Before treatment, the number of infected deer was similar (area to be treated: 8/9; baited control: 4/8; unbaited control: 5/8). In winter 1987–1989, at each of 10 sites across a 391-ha treatment pasture and 10 sites across 421-ha of baited control pasture, untreated corn was distributed for 3–4 weeks, before corn containing triclabendazole (500 ml triclabendazole/23 kg corn) was used in the treatment pasture for a further week. The estimated dose was 11 mg/kg body weight/deer/day for seven days. Corn was placed at dusk, and deer were counted at each bait site between 2100–2300 hr. At a third, 439-ha unbaited control pasture, no corn was distributed. In January 1987, before baiting began, 13 fawns and 12 adult deer were shot across the three areas. In 1987–1989, four weeks after baiting finished, 6–15 adult deer were shot on each pasture. The liver of each deer was examined for parasites.

4 

A randomized, replicated, controlled study in 1991–1995 in two mountain ranges in Colorado, USA (Miller et al. 2000) found that medical treatment of Rocky Mountain bighorn sheep Ovis canadensis canadensis against lungworm did not increase lamb survival. Average annual recruitment did not differ between herds treated for lungworm (0.5–0.7 lambs/adult female) and untreated herds (0.6–0.7 lambs/adult female). Adult bighorn females of four herds were captured in February–March 1991–1995 and were marked and radio-collared. Between 1991 and 1995 the herds were either fed for 8–10 weeks each winter with 2 kg/individual/day of alfalfa hay and 1 kg/individual/day of apple pulp, fed with alfalfa hay and apple pulp with two treatments of a drug to reduce parasitic worms (Fenbendazole, 3 g/adult female) added to the apple pulp late in the feeding period, given Fenbendazole-treated salt blocks (1.65 g Fenbendazole/kg) from December to April, or not given food or Fenbendazole-treated salt blocks. Treatments were rotated annually under a predetermined, randomly selected scheme. Lamb survival for 11–18 marked adult females/herd was assessed every two weeks between May and October.

5 

A replicated, controlled, before-and-after study in 1988 in a mountainous National Park in southern Spain (León-Vizcaíno et al. 2001) found that injecting Spanish ibex Capra pyrenaica hispanica with higher doses of ivermectin treated sarcoptic mange Sarcoptes scabiei faster than lower doses, and treatment was more effective in animals with less severe infections. All nine ibex with limited mange recovered after being treated with ivermectin. Six animals injected with 0.4 mg/kg body weight had no scabs or mites 21 days after treatment, and three animals injected with 0.2 mg/kg body weight had no scabs or mites four and five weeks after treatment, respectively. However, only three of six ibex with severe infection recovered following treatment, and two died. The sixth animal was still carrying mites two months after treatment. From September–December 1988, wild Spanish ibex were caught, sedated, and treated with Foxim anti-mange treatment (500 mg/l of water). Fifteen adult (>2-years old) female ibex with sarcoptic mange were divided into five treatment groups: 1) ibex with limited mange, given a single dose of ivermectin (0.4 mg/kg body weight) by syringe injection; 2) ibex with limited mange given a single dose of ivermectin (0.4 mg/kg body weight) by rifle dart injection; 3) ibex with limited mange given a single dose of ivermectin (0.2 mg/kg body weight) by syringe; 4) ibex with severe mange given two doses of ivermectin (0.2 mg/kg body weight) by syringe, two weeks apart; 5) ibex with severe mange given two doses of ivermectin (0.4 mg/kg body weight) by syringe, two weeks apart. Infection was classified into four levels of severity, and treatment tested on the worst two: limited (“consolidation”: affected skin limited to a few body parts) and severe (“chronic”: severe skin disease covering much of the body). Ibex were examined for two months to monitor recovery.

6 

A replicated, before-and-after study in 1989 in a mountainous National Park in southern Spain (León-Vizcaíno et al. 2001) found that after injecting Spanish ibex Capra pyrenaica hispanica with ivermectin to treat sarcoptic mange Sarcoptes scabiei, a mange-free herd was established. All 32 Spanish ibex treated with ivermectin showed no signs of mange six weeks after treatment began. After joining 65 mange-free ibex (at least 12 of which were treated in an earlier program, and 17 of which were mange-free on capture), the total population of 97 ibex showed no signs of mange for at least a year. From February–March 1989, sixty-three Spanish ibex were caught, sedated and examined for sarcoptic mange. The 14 ibex with chronic mange were injected with ivermectin (0.4 mg/kg body weight) and released at the capture site. The 49 remaining ibex, including healthy animals, were injected with ivermectin (0.4 mg/kg body weight) and a foxim spray (500 mg/l), and examined for mites. The 17 animals without mites were placed in “quarantine” pens, and 32 with mites were kept in “treatment” pens and injected with ivermectin (0.2 mg/kg body weight) two- and four-weeks later before joining the “quarantine” pens. After two weeks in quarantine, ibex showing no symptoms of mange were given a final dose of ivermectin and released into a 400-ha enclosure in Nava de San Pedro Park which already contained 48 ibex.

7 

A replicated, before-and-after study in three sites in Slavonia, Croatia (Rajkovi-Janje  et al. 2004) found that using drugs to treat parasites reduced the number of parasite eggs in the dung of wild boar Sus scrofa piglets. These results were not tested for statistical significance. After 14 days, parasite eggs were found in 0–10% of piglet faecal samples compared to 70–100% before treatment. The anti-parasitic drug ivermectin (0.6% formulation) was mixed with piglet feed at a concentration of 9 parts per million. An unspecified number of piglets in three sites were offered the feed for seven days using semi-automated piglet feeders, which were refilled twice each week. Faecal samples from the piglets were examined before the treatment and after seven and 14 days.

Referenced papers

Please cite as:

Littlewood, N.A., Rocha, R., Smith, R.K., Martin, P.A., Lockhart, S.L., Schoonover, R.F., Wilman, E., Bladon, A.J., Sainsbury, K.A., Pimm S. and Sutherland, W.J. (2020) Terrestrial Mammal Conservation: Global Evidence for the Effects of Interventions for terrestrial mammals excluding bats and primates. Synopses of Conservation Evidence Series. University of Cambridge, Cambridge, UK.