Establishing an efficacious dose rate of monepantel for treating gastrointestinal nematodes in llamas under field conditions.
In Europe, the importance of domesticated South American Camelids (SAC), llamas (Lama glama) and alpacas (Lama pacos), has grown, especially in recent years, due to their rising popularity and the associated increase in their numbers. SACs are classified as ‘food producing animals’ within the European Union. Thus, special guidelines need to be followed in the case of pharmacological treatment. For llamas and alpacas, drugs are used in an extra-label manner, since appropriate veterinary medicinal products are only authorised for domestic foodproducing species such as horses, goats, sheep or cattle, but not for camelids. Endoparasitism is a major health concern in SACs causing severe clinical diseases and economic losses. Especially, gastrointestinal nematode (GIn) infections are common in llamas and alpacas kept in Europe. This is not surprising given that camelids often share grazing with sheep, goats and cattle, or are kept on pastures previously used for ruminants. Cross-transmission between host species can take place (Bishop and Rickard 1987) and GIn common to sheep and cattle have been documented in camelids as well (Leguia 1991, Rickard 1994, Fowler 2010). There are several classes of anthelmintics frequently used in all ruminants, including benzimidazoles, macrocyclic lactones, imidazothiazoles and hydropyrimidines. For anthelmintic drugs, very few data are published on proper dose regimen in SACs. It is difficult to estimate whether anthelmintic drugs applied at dose rates and routes suggested for horses, sheep or cattle lead to drug levels able to effectively eliminate GIn in SACs as well. The potential risk for underdosing, and the associated risk for the development of anthelmintic resistance are therefore high. As anthelmintic resistance to all groups of broad-spectrum antiparasitics has been widely reported in livestock (Kaplan 2004, Wolstenholme and others 2004, Coles and others 2006), the development of novel anthelmintics is very important for the control of multiresistant nematodes worldwide. Monepantel was the first compound of such a new anthelmintic class, the so called ‘aminoacetonitrile derivatives’, that entered the market. It is licensed for oral use in sheep infected with GIn. High efficacy was demonstrated when administered to sheep at 2.5mg/kg bodyweight (BW) (Hosking and others 2009). Efficacy of monepantel in SACs has not been shown yet. Thus, a study was designed to evaluate the efficacy of monepantel at three different dose rates in llamas under field conditions. Forty-six llamas from four different farms located in Austria were studied at two occasions: before and two weeks after treatment. All animals were healthy as determined by physical examination. Faecal examinations confirmed natural infection with GIn. Animals were not wormed within the last five months. The animals were weighed and randomly allocated to three treatment groups and one control group. Monepantel (Zolvix, novartis Healthcare, Denmark), was used off-label. Animals were dosed orally using a calibrated drenching gun. Group 1 (n=16) was given the dose rate recommended for sheep (2.5mg/kg BW), group 2 (n=12) was treated with 5mg/kg, and group 3 (n=12) with 7.5mg/kg. An untreated control group (n=6) was used for monitoring natural changes in egg counts during the study. Faecal samples were collected directly from the rectum of each animal and examined on the same day, or stored at 4°C for processing next day. The employees performing faecal examinations were not aware of the treatment status of the respective animals. The criteria for efficacy was based on faecal egg count (FEC) reduction (FECR per cent) and extensity effect (EE per cent). The FECR values were calculated on day 14 based on means of FECs using Coles formula (Coles and others 1992). A 95 per cent CI is provided. The FEC was determined by using a modified McMaster technique with each counted egg representing 25 eggs per gram (EPG). EEs were calculated based on the formula: EE per cent=100× (number of negative animals on day 14/number of positive animals on day 0). Study procedures were discussed and approved by the institutional ethics committee in accordance with Good Scientific Practice Guidelines and national legislation. Mean EPGs were assessed before and 14days after treatment (Table 1). FECR per cent and EE per cent were calculated from data obtained from samples collected two weeks after treatment (Table 2). none of the animals showed adverse reactions to the treatment. It has been shown that oral application of monepantel in sheep at 2.5mg/kg results in generally >99 per cent reduction of nematode eggs shed with the faeces (Sager and others 2009). This dose rate, recommended for sheep, did not lead to effective results in llamas. Seventy per