Use drugs to treat parasites

Overall effectiveness category Likely to be beneficial
Number of studies: 2
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How is the evidence assessed?

Effectiveness

50%
Certainty

40%
Harms

10%

Calculating overall effectiveness category

Background information and definitions

High parasite loads may reduce the fitness of marine and freshwater mammals and lead to higher levels of mortality (Aznar et al. 2001). Drugs are available to reduce the infestation levels of some parasites. Attempts to treat wild marine and freshwater mammals are most likely to be made when a species is highly threatened or when there are public health risks or economic costs associated with not treating. In such cases, mammals may be captured, treated, and released with the aim of improving the health of wild populations. For studies that treated mammals for parasites in captivity as part of a rehabilitation programme, see Rehabilitate and release injured, sick or weak marine and freshwater mammals.

Aznar F.J., Balbuena J.A., Fernández M. & Raga J.A. (2001) Living together: the parasites of marine mammals. Pages 385–423 in: Evans P. G. H. & Raga J. A. (eds.) Marine Mammals: Biology and Conservation. Springer US, Boston, MA.

Study locations

Key messages

Two studies evaluated the effects on marine mammals of using drugs to treat parasites. Both studies were in the North Pacific Ocean (USA).

COMMUNITY RESPONSE (0 STUDIES)

POPULATION RESPONSE (2 STUDIES)

Survival (2 studies): One of two controlled studies (including one before-and-after study) in the North Pacific Ocean found that treating northern fur seal pups with an anti-parasitic drug (ivermectin) reduced mortality rates. The other study found that Hawaiian monk seal pups treated with an anti-parasitic drug (praziquantel) had similar survival rates to untreated pups.
Condition (2 studies): One of two controlled studies (including one before-and-after study) in the North Pacific Ocean found that northern fur seal pups treated with an anti-parasitic drug (ivermectin) had reduced hookworm infections and greater growth rates than untreated pups. The other study found that Hawaiian monk seal pups treated with an anti-parasitic drug (praziquantel) had similar parasite loads to untreated pups.

BEHAVIOUR (0 STUDIES)

About key messages

Key messages provide a descriptive index to studies we have found that test this intervention.

Studies are not directly comparable or of equal value. When making decisions based on this evidence, you should consider factors such as study size, study design, reported metrics and relevance of the study to your situation, rather than simply counting the number of studies that support a particular interpretation.

Supporting evidence from individual studies

A controlled, before-and-after study in 2006 on an island in the North Pacific Ocean, off the coast of California, USA (DeLong et al. 2009) found that northern fur seal Callorhinus ursinus pups treated with an anti-parasitic drug (ivermectin) had reduced hookworm Uncinaria lucasi infections, lower mortality rates and greater growth rates than untreated pups. The number of treated pups with hookworm infections decreased from 24% (36 of 151 pups) to 6% (2 of 34 pups) 19–34 days after treatment with ivermectin. In comparison, the number of infected untreated pups increased from 24% (36 of 149 pups) to 67% (20 of 30 pups). Mortality rates were lower for pups treated with ivermectin (10 of 149 pups died, 7%) than untreated pups (50 of 151 pups died, 33%), and growth rates were greater (treated: 0.06 kg/day; untreated: 0.04 kg/day). In July 2006, seal pups were captured, tagged and alternately assigned to a treatment group (injected with ivermectin; 151 pups) or untreated control group (injected with saline solution; 149 pups). Hookworm eggs were counted in faecal samples in July (all of 300 pups) and August 2006 (34 treated pups, 30 untreated pups). Pups were weighed in July (all of 300 pups) and September 2006 (number not reported). Mortality surveys were carried out every 3–20 days in July–December 2006.
Study and other actions tested
Referenced paper
DeLong R.L., Orr A.J., Jenkinson R.S. & Lyons E.T. (2009) Treatment of northern fur seal (Callorhinus ursinus) pups with ivermectin reduces hookworm-induced mortality. Marine Mammal Science, 25, 944-948.
A controlled study in 2009–2010 on an island in the North Pacific Ocean, Hawaii, USA (Gobush et al. 2011) found that Hawaiian monk seal Monachus schauinslandi pups treated with an anti-parasitic drug (praziquantel) had similar parasite loads and survival rates to untreated pups. The number of faecal samples containing parasitic worms (cestodes Diphyllobothrium spp.) did not differ significantly between treated pups (44 of 46 samples, 96%) and untreated pups (43 of 44 samples, 98%). Survival rates also did not differ significantly between treated pups (20 of 23 pups survived, 87%) and untreated pups (19 of 20 pups survived, 95%). Forty-three tagged seal pups (<2 years old) were randomly assigned to a treatment group (injected with praziquantel; 23 pups) or an untreated control group (20 pups). Each of 43 pups was captured, weighed, measured, injected (treatment group only) and had faeces sampled up to four times, 8–16 weeks apart, between December 2009 and May 2010.
Study and other actions tested
Referenced paper
Gobush K.S., Baker J.D. & Gulland F.M.D. (2011) Effectiveness of an antihelminthic treatment in improving the body condition and survival of Hawaiian monk seals. Endangered Species Research, 15, 29-37.

Please cite as:

Berthinussen, A., Smith, R.K. and Sutherland, W.J. (2021) Marine and Freshwater Mammal Conservation: Global Evidence for the Effects of Interventions. Conservation Evidence Series Synopses. University of Cambridge, Cambridge, UK.

Where has this evidence come from?

List of journals searched by synopsis

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This Action forms part of the Action Synopsis:

Marine and Freshwater Mammal Conservation

Related Actions

Actions	Effectiveness	Studies	Category
Vaccinate against disease Action Link	No evidence found (no assessment)	0	Synopsis Link
Use drugs to treat parasites Action Link	Likely to be beneficial	2	Synopsis Link
Translocate or temporarily bring marine and freshwater mammals into captivity to reduce exposure to disease Action Link	No evidence found (no assessment)	0	Synopsis Link