Vet Parasitol. 2016 Mar 15;218:98-101. doi: 10.1016/j.vetpar.2016.01.009.
Efficacy and persistent activity of moxidectin against natural Muellerius capillaris infection in goats and pathological consequences of muelleriosis.
Jaroslav Vadlejcha,∗, Pavol Makovickyb, Zuzana Cadkováa, Iva Langrováa
a Department of Zoology and Fisheries, Faculty of Agrobiology, Food and Natural Resources, Czech University of Life Sciences Prague, Kam´ycká 957, 165 21
Prague 6–Suchdol, Czech Republic
b Department of Biology, Pedagogical Faculty, Selye János University, Bratislavska 3322, 945 01 Komarno, Slovak Republic
The effect of moxidectin against natural Muellerius capillaris infection in goats was evaluated in this study. Long-acting moxidectin at a single dose of 1 mg kg(-1) body weight was administered to an entire flock (n=10) of goats. The individual faecal larval count reduction was applied as an indicator of treatment efficacy. A significant reduction (>98%) in larval counts was observed in all surveyed animals 14 days after drug administration. Moxidectin demonstrated persistent activity in this study; the mean faecal larval count reduction was 99.1% ± 1.8 on day 77 of the treatment. Macroscopic abnormalities and histological changes in the lungs of two infected goats were evident during the post-mortem examination. The pathological consequences of M. capillaris infection were observed even three months after parasite elimination. The results of this study indicate that moxidectin is a highly effective anthelmintic agent for the control of muelleriosis in goats. This drug provides animals with fifteen weeks of protections against M. capillaris reinfection.
KEYWORDS: Goat; Moxidectin; Muellerius capillaris; Pathology
Muelleriosis is a parasitic disease caused by the nematode Muellerius capillaris. This parasite is one of several small lungworm species that infects lung parenchyma of both domestic and wild ruminants worldwide. Goats become infected by unintentionally ingesting molluscs that contain Muellerius third stage larvae. More than sixty species of snails and slugs have been recognised as suitable intermediate hosts for M. capillaris. Adult nematodes are present in the definitive host lungs 6 to10 weeks after infection. The patent period, when first stage larvae are shed in host faeces, generally exceeds two years.
Muelleriosis in domestic small ruminants is often overlooked due to its asymptomatic or subclinical character; however, productivity in goats could be affected as a consequence of this infection. The correlation between Muellerius infection and decreased body weight (1), lung tissue damage due to inflammatory reaction (2) and impaired respiratory function were described in goats infected with M. capillaris (3). There is a possible indirect effect of Muellerius infection that is also worth considering: lungs affected by muelleriosis are more susceptible to secondary bacterial or viral infection (4).
The control of Muellerius infection, which relies largely on the use of broad spectrum anthelmintic drugs (primarily benzimidazoles and macrocyclic lactones), is generally complicated. Anthelmintics are more likely to reduce small lungworm fecundity, resulting in a decrease in the faecal larval count rather than an elimination of all adult nematodes. Benzimidazoles such as fenbendazole and albendazole are moderately efficient against muelleriosis in goats; however, doses higher than those recommended by the manufacturer for the treatment of gastrointestinal nematodes, as well as repeated drenching are necessary (5). Not even ivermectin (macrocyclic lactone) is fully effective against muelleriosis in goats; almost one quarter of treated animals resume larvae shedding four weeks after the administration of ivermectin at the recommended dose for gastrointestinal nematode infections (6). One can apply eprinomectin (macrocyclic lactone), which completely eliminates M. capillaris faecal larval counts in goats for a period of six weeks (7). However, this drug is licensed for cattle, and the pour-on application is impractical for long-haired goat breeds.
In 2013, we revealed, based on coprological examination, a small lungworm infection in all animals from a goat herd kept for demonstrational/educational purposes at the Czech University of Life Sciences Prague. Some animals suffered from a severe infection that manifested itself through coughing and difficulty breathing. Taking into account our experiences treating small lungworm infections using traditional anthelmintics as well as literary data to this topic, we decided to apply an experimental treatment using moxidectin – a macrocyclic lactone drug that differes from ivermectin in the activity. We hypothesized that the above-mentioned anthelmintic drug might be more efficient against M. capillaris infection than are traditionally used drugs.
Table 1. The individual faecal larval counts before (D0) and after (at weekly intervals D7 – D105) moxidectin treatment.
Because moxidectin is not licensed for goats and there is no recommended dosage for them, we administered long-acting moxidectin (Cydectin 2% LA) to the surveyed animals at doses for sheep (1 mg.kg-1 body weight, s.c.). We evaluated treatment efficacy based on a reduction in faecal larval counts before and after moxidectin application. We noted that faecal larval counts significantly decreased 14 days after treatment (see table 1) in all surveyed goats and at that time respiratory symptoms in animals disappeared. Morevover, moxidectin (at the selected dosage) demonstrated persistent activity; high drug efficacy against muelleriosis was observed in all of the surveyed animals even two months after application (see table 1). As is evident, our hypothesis was confirmed.
Considering the lack of information regarding the impact of M. capillaris infection on goat lung tissue, we decided to carry out a post-mortem examination of the lungs from two goats. These animals were selected according to their infection intensity levels before and after drug application. We hypothesized that pathological consequences due to muelleriosis might correlate with infection intensity. Even though we detected parasitic elements (see fig. 1) exclusively in tissue from seriously infected goat, histological regressive changes (e.g. thickening of the alveolar septa, smooth muscle cell hypertrophy, fibrous reconstruction of the tissue, inflammatory infiltration and pseudo-granulomatous formation) were evident in both, heavy infected animal and its counterpart (see figs 1 and 2). Based on the above mentioned-results, a second hypothesis was not confirmed.
Fig. 1. Histological section of the goat lungs severely infected by Muellerius capillaris: la – larvae, ra – residual alveoli, smc – smooth muscle cells, ici – inflammatory cell infiltrate.
The importance of our study is two-fold. Firstly, it clearly demonstrates that moxidectin at a dose of 1 mg.kg-1 eliminates muelleriosis in goats, and also that these animals are protected against M. capillaris reinfection for at least 15 weeks after tratment. Even though moxidectin is not licensed for use in goats, it is a welcome choice in the control of muelleriosis in these animals. However, it is necessary to refrain from administering moxidectin to milk-producing goats due to its persistency.
Secondly, this study shows that infection caused by M. capillaris can have a significant negative impact on pulmonary parenchyma in goats. This would include marked changes in lung morphology and a strong inflammatory response to parasitic infection. Our results also indicate that the elimination of muelleriosis and the regeneration of goat lung tissue are long-term, demanding processes. Knowledge of small lungworm infection in goats is still limited, and its veterinary significance has yet to be fully recognized.
Fig. 2. Histological section of the goat lungs with negligible Muellerius capillaris faecal larval counts: smc – smooth muscle cells, ici – inflammatory cell infiltrate.
Jaroslav Vadlejch, Ph.D.
Associate Professor of Applied Zoology
Czech University of Life Sciences Prague
Faculty of Agrobiology, Food & Natural Resources
Dept. of Zoology and Fisheries
Kamýcká 957, 165 21 Prague 6 – Suchdol, Czech Republic
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