Lauren Else & Richard Wall
New approaches to the management of mange
Lauren Ellse & Richard Wall
Mange is one of the most difficult to control parasitic conditions in alpacas, causing welfare issues for the animals and economic loss for their owners. The condition is widespread and a large proportion of UK herds suffer from some type of mange each year (Lusat et al., 2009). The severe irritation and stress some alpacas experience with mite infestations are caused by an immune hypersensitivity reaction which leads to alopecia, dermal scaling and crusting as well as skin and fleece damage caused by animal rubbing and scratching. In chronic cases a wrinkling and thickening of the skin may occur (Figure 1).
The mange appears to occur year round, with many owners suggesting that they see it more often in summer (Figure 2), although this may be because it is more visible after shearing. In other cases it appears to be more common in winter and early spring, when animals may be housed and in poorer body condition. The precise pattern may depend on the specific conditions and seasonal husbandry in each herd.
Even at times when animals appear to recover from mange it may then reappear a few months later, because the mites have not disappeared completely. Small populations have remained hidden away in protected locations such as wrinkles in the skin or the ears, only to re-emerge some months later. This apparent regression of the infestation is important because during this period asymptomatic animals may in reality carry small populations of mites and thus act as carriers. These carriers may then be introduced to other flocks and subsequently initiate outbreaks.
Three types of mite are primarily responsible for mange problems in alpaca: Chorioptes, Sarcoptes, and Psoroptes. All life-cycle stages are found permanently on the host and transmission is primarily through physical contact between infested individuals and also from mother to offspring at suckling. Hence, periods of handling or housing, when animals are crowded together, are key points in promoting the spread of mites. Transmission may also occur via the environment, if the environmental conditions are suitable, mites can survive for up to three weeks in animal bedding, housing and contaminated equipment. Therefore, this off-host survival period should be considered when trying to control the mites, since it determines the time in which potentially infected areas on the farm must be kept clear, to ensure that treated animals do not become re-infested.
Mange is a very difficult condition to control. The macrocyclic lactones (e.g. ivermectin) are the most widely used therapeutic choice however, these products are not licenced for use in camelids and the choice of dose requires considerable care. Selection of a dose appropriate for a sheep may result in significant under-dosing and ongoing infection. In addition, the relatively short period of residual activity of some of these compounds, means that animals must be moved to clean housing following initial treatment which can present major difficulties for many owners. In addition, most treatments do not moisturise or relieve the irritated skin associated with clinical presentations of mange, therefore emollient cream application is often required in parallel or after treatment to repair the skin. Dosing a single infected animal with a macrocyclic lactone and then returning it to the herd is unlikely to give clearance of the condition.
Over time, persistent under-dosing of herds is likely to hasten the onset of parasite resistance, both in mites and the parasitic worms that will be unintentionally exposed to the drug and the development of drug resistance will progressively undermine the use of conventional acaricides. In addition, restrictions on the use of some insecticides such as amitraz, organophosphates and pyrethroids, on environmental and safety grounds, has led to increased interest in the development of alternative approaches to ectoparasite management. The use of essential oils and their extracts is one such area of interest as many have shown a high level of biological activity against a range of parasite species including mites (Ellse et al., 2013).
Essential oils are blends of approximately 20-80 different plant metabolites which are usually extracted by condensing steam which has been passed through plant material. These metabolites are volatile molecules of low molecular weight. Essential oils usually contain two or three major terpene or terpenoid components, which constitute up to 30% of the oil. The insecticidal/acaricidal efficacy is often attributed to the oil?s major component(s). The mode of action of many essential oils or components is largely unknown although there is evidence of a toxic effect on the parasite nervous system. For example terpinen-4-ol, a monoterpenoid found at high concentration in tea tree oil, inhibits arthropod acetylcholinesterase, an enzyme essential for transmission of action potentials. Alternatively, the hydrophobic nature of the oils may simultaneously exert mechanical effects on the parasite such as disruption of their cuticular waxes and blocking their ability to respire leading to death by water stress or suffocation.
Recent studies have demonstrated that many essential oils may be used to help control ectoparasites such as lice and mites. Toxicity has been shown following immersion and physical contact with treated surfaces, but also after exposure to the vapour of these oils. Work carried out at the University of Bristol has demonstrated that application of an extract of an essential oil completely cleared mange (sheep scab) caused by the mite, Psoroptes ovis, in seven of eight sheep after a single application, while significantly lowering the mite burden in the eighth animal. Laboratory contact assays using sheep scab mites also indicated high acaricidal activity and that the efficacy was maintained for up to 96 hours. However, getting the concentration and formulation right is important; many products on the market that contain very low concentrations of essential oil, or have the oil in an inappropriate formulation, are unlikely to have any effect.
Following on from previous work, in a study carried out this year in the south west of England, five alpaca farms with a history of mite infestation were asked to apply a cream containing essential oil extract to crusty lesions as part of their usual management routine. Photographs and a questionnaire were used to gauge the efficacy of the application. There was an overwhelmingly positive response, with visible improvement in many animals, such as scab/scale removal, softening of the skin and hair regrowth. The effect was so marked that most of the participants in the study have asked for a resupply of the cream and the product has now been made available commercially as ?Alpaca Scab Dab? (www.agrientlimited.com). It is not a veterinary medicine but an effective emollient which helps thickened, scaled skin to recover and represents a real alternative to this persistent problem.
Ellse, L. & Wall, R. (2013) The use of essential oils in veterinary ectoparasite control: a review. Medical & Veterinary Entomology, 28, 233-243.
Lusat, J.,Morgan, E.R. & Wall, R. (2009) Mange in alpaca, llama and goats in the UK: incidence and risk Veterinary Parasitology, 163, 179-184