GLOBALLY, THE well-being of animals is a matter of continuous onslaught by parasites; with a major category of arthropod ectoparasites affecting animal population on land. These ectoparasites represent a number of forms of parasitic associations with their hosts; permanent and intermittent, obligate and facultative, cutaneous and subcutaneous, etc. Arthropod ectoparasites are capable of inflicting great economic losses to livestock industry by producing direct nuisance and vectoring multiple pathogens. In view of these threats, an effective control strategy needs to be launched. Systemically applied chemicals have been widely and effectively used against these parasites because of their low cost, high efficacy and ease of application. However, from the past few years, increasing health and scientific concerns are associated with almost all the groups of chemical insecticides including; organophosphates, organochlorines, pyrethroids, carbamates, growth inhibitors, etc. But, factors like (i) development of resistance, (ii) scarcity of development of new compounds, and (iii) increased side effects like neurotoxicity in hosts limit their use as sustainable control measure.
This emphasizes to jot down a comprehensive and integrated approach for controlling ectoparasitic population on livestock and humans. This may include:
a) Managemental tools that encompass micro-management; improved nutrition, body hygiene (grooming), grazing concerns, regular monitoring of animals for questing population of arthropods, and macro-management; Farm/housing hygiene, type of housing, floor pattern, litter change frequency, disinfection and elimination of cracks and crevices, and off-host management. Off-host parasite control strategies can provide considerable advantage in integrated control programmes. In this regard, traps and screens have been applied in different field conditions to control those life stages of ticks, mites, and flies that stay away from the host. Odor baited catching devices and insecticide impregnated traps can increase the efficiency, especially against myiasis causing flies. Managemental tools help improve health status of livestock and poultry population thus lowering the risk of arthropod infestation. Special consideration should be paid to prophylactic strategies. These include all the measures taken to reduce the chances of infestation in risky seasons of the year. In Pakistan, generally climate is hot and humid which is much favorable for arthropods; risky period starts from April and extends to October. Before arrival of risky periods breeding habitats of arthropods should be minimized, shearing can be done to avoid fly strike, dung/litter should be disposed of, and immunization can also be done in endemic areas.
b) Selective breeding and improved nutritional status do a supporting job in the integrated control system. Selective breeding employs use of genetic resistance against disease or arthropod vector. The genetic pool can be exploited within or between breeds but through approved national or international policies.
c) Selection of compounds having conserved the optimum efficacy of available compounds. Rational and recommended use of the selected drugs is crucial for maintaining the efficacy; following the principles of dose/dosage, and rotation. While using drug it should be ensure that the whole population of the particular area or farm is receiving that drug. A general pharmacological rule should be kept in mind that each candidate compound reaching market for its therapeutic use, shows few or more years of its potent activity after which resistance has to develop irrespective of the mechanism it follows, thus, it proves the need for development of new drug candidates and rotation or replacement of old with emerging compounds.
d) Evaluation of sophisticated alternates for early diagnosis of microscopic ectoparsites on the host and in habitats.
e) Immunological control remains another encouraging option in face of controlling parasitism as ectoparasites elicit a protective immune response inside the host body. The understanding of immune mechanisms of parasite-host interface provides vaccine candidates against ectoparasites. These immune mechanisms can be employed in two ways; exposure of host to certain parasite molecules to elicit protective immune response and targeting parasite by introducing pathogenic substances into the parasite through blood meal. Tick vaccines have been used in various parts of the world which reduce tick population by reduction in egg laying ability of female ticks. Ectoparasitic control by immunization is very effective and specific without the complication of residues. Maintenance of acceptable level of ectoparasites in the environment may help in indirect control of losses caused by artropodes. This will expose the animals to pathogens in order to allow their natural immune system to generate sufficient protective tools against those very pathogens.
f) Biological control measures to reduce the population of parasites in the environment. The use of naturally occurring pathogens; nematodes, bacteria, virus, and fungi offers a better alternative to control ectoparasites. For example, bacteria (Bacillus thuringiensis) and certain wasps can control parasitic flies (blow fly, house fly, and stable fly). Similarly, few fungal species have shown acaricidal activity against several species of ticks and mites. Experimental trials have shown that these biological agents can prove promising in clinical cases of ectoparasitism, when standardized for commercial formulations
As an alternative to chemicals, integrated control programmes are proposed with management tactics incorporating parasiticides as one component. Integrated control programmes integrate management practices, rational use of pesticides, selective genetic management, and biological control tools. Although, conventional chemical methods have shown potent activity against ectoparasites during last few decades but their abrupt and extensive usage has led to ongoing problems. It can be concluded that integrated control programme for ectoparasites should be executed with coherent use of insecticides, thus preserving their availability and to safeguard human and animal health in better way. Given perspective alarms farmers, scientists, and policy makers to take measures in combating the challenges instigated by ectoparasitism. Scientists need to explore advanced areas of diagnostics, screening of susceptible populations, vaccinations, and identification of resistance. Duties of NGOs and policy makers cannot be overlooked; they can play their role in designing policies in execution of integrated control strategies, screening of inefficacious drugs, minimizing quackery in treatment and control of ectoparasitism, and in recognition of the significant role of veterinarians, particularly parasitologists.
The writers are associated with the Department of Parasitology, University of Agriculture, Faisalabad.
By Dr. Qurat-ul-Ain, Dr. M Sohail Sajid and Dr. Zafar Iqbal