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Parasitology Notes

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Parasitology

1. Introduction Ectoparasite treatment may aim to control or to eradicate a particular parasite. Eradication is complete removal of a parasite. An attempt was made to eradicate malaria by eradicating the mosquito Anopheles, however this attempt failed due to insecticide resistance, socio-economic factors and poor surveillance. Control is a reduction of parasite load or vector population, thus reducing transmission. The object is to reduce the disease/pest level to an acceptable level. Most ectoparasiticides act as neurotoxins. These act on CNS synapses, axons or neuromuscular junctions, causing a spastic or flaccid paralysis. Some examples of neurotoxin ectoparasiticides are listed below: Group Organophosphat es Carbamates

Example Fenthion, diazinon

Triazepentadien es

Action Cholinesterase inhibitor Cholinesterase inhibitor Octopamine receptor stimulant

Phenylpyrazoles

GABA inhibitor

Fipronil, pyriprole

Neonincatinoids

Nicotinic Ach receptor stimulant Sodium channel activator Sodium channel activator

Imidacloprid, nitempyram Dichlorvos, fenitrothion Permethrin, flumethrin

Sodium channel blocker Chloride channel activators

Metafluminizone, indoxacarb Avermectins: ivermectin, selamectin Milbemycins: milbemycin oxime, moxidectin Spinosad

Pyrethrins Pyrethroids

Semicarbazones Macrocyclic lactones

Spinosyns

Nicotinic Ach receptor stimulant and GABA agonist

Notes

Propoxur, carbaryl Amitraz

Used for lice control in cattle/pigs. Contraindicated in horses and cats. Fipronil toxic to rabbits.

Toxic to cats. Toxic to cats (except flumethrin collar)

Possible neurotoxicity in collies

2. Control of ectoparasites

2.1

Fleas

Fleas are of the order Siphonaptera. The cat flea, Ctenocephalides felis, is the most common flea of both cats and dogs. The lifecycle of the flea means that only the adult stage is present on the animal. The life cycle is also effected by the environment - temperatures of 3°C will kill pupae and eggs. Dog and cat fleas are therefore more common in the south of Britain.

Physical control measures include washing pet blankets, rugs and carriers above 60°C to remove eggs and larvae. It is also important to maintain a clean environment - for example, hovering to remove eggs from sofas and carpets. There are chemical control products available that affect the adult, larval and egg stage cycles. An additional environmental spray containing adulticide and insect growth regulator is required to thoroughly eliminate the parasite. As the pupa stage is unaffected by all treatments, it may take up to 3 months to eliminate all fleas.

2.2

Lice

Lice can be sucking or chewing lice. A list of lice genus is below: Sucking lice Haematopinus Linognathus

Chewing lice Damalinia Felicola Trichodectes Lipeurus Cuclotogaster Menacanthus Gliricola Gyropus

They spend their whole life cycle on the host, so control is simple and effective. Effective products include topical organophosphates, pyrethoids, topical avermectins, ivermectin inject (for sucking lice only) and amitraz for use in cattle and pigs. It is also important to attent to environmental hygiene and management, as heavy infestations are usually associated with animals in poor health or sanitary conditions. Lice can move off the animal and survive in the environment for a couple of days, and may then be picked up again by the animal.

2.3

Flies

Blood feeding flies include stable flies, tabanids, horn flies and Culicoidies. Control measures for these flies aim to kill and few flies and to repel. Measures include fly avoidance, repellants, topical insecticides and physical barriers. Some of these flies act as vectors, for example Culicoides as vectors of bluetongue and Schmallenberg virus. Keds affect sheep and are wingless blood-feeding flies that spend their whole lifecycle on the host. Many are removed by shearing, but they can also be killed by topical insecticides. Nuisance flies include house and face flies. They can be controlled using topical organophosphates or pyrethroids. Myiasis is often caused by warble flies (Hypoderma) or blowfly strike (Lucilia sericata) and rarely the house fly (Musca domestica). Blow flies include the species Lucilia sericata. The females lay eggs into a crevice, carcass or wound, which can take up to 3 days to hatch depending on temperature. Larvae feed directly off the sheep's skin, causing massive lesions and secondary infections. The larvae then drop off and enter a pupal stage in the soil. Treatment for blowfly strike include use of topical treatments, including:





Alpha-cypermethrin (Dysect, zermasect) Cypermethrin (Crovect, ectofly) Cryomazine (Vetrazin) Dicyclanil (Clik) Deltamethrin (Coper's spot on) Diazinon (sheep dip)

Warble flies are of the genus Hypoderma, and belong to a group of obligate myiasis (flesh-eating) causing flies in the family Oestridae, which includes many bot flies including the horse bot fly (Gasterophilus) and the sheep nasal bot fly (Oestrus). Warble fly infection is a notifiable disease in the UK.

2.4

Ticks

Ticks are divided into hard and soft ticks. Soft or argasid ticks are nidicolous or nest-living. Hard or ixodid ticks are non-nidicolous or non-nest -living. a) Tick borne diseases Ticks are important as they can be vectors of disease. The following diseases are all tick-borne, with the most important highlighted: Protozoal Babesiosis Theleriosis Anaplasmosis

Bacterial Lyme disease (Borreliosis) Ehrlichiosis Spotted fever group

Viral Louping ill Equine encephalomyelitis African swine fever Q fever

Ixodes ricinus transmits Lyme disease, louping ill virus, Ehrlichia and Babesia in cattle. It is common in the UK. Dermacentor reticulatus transmits Babesia canis, but is rarely found in the UK. Rhipicephalus sanguineus transmits Babesia canis and Ehrlichia canis, but is found only in southern Europe. Lyme disease is caused by corkscrew shaped bacteria called Borrelia burgdorferi. It causes rashes in the pattern of a 'bulls-eye' at the site of the tick bite. Louping ill is also known as infectious ovine encephalomyelitis. It causes disease in sheep and grouse in upland areas. The virus attacks the CNS. Disease control is voluntary and includes use of acarides and an inactivated vaccine against the virus. Babesia spp. are intraerythrocytic protozoan parasites. Infection results in destruction of erythrocytes, resulting in severe anaemia. There are a number of Babesia spp. which have different hosts, for example Babesia bovis that affects cattle and buffalo. Babesiosis in cattle in the UK (redwater fever) is caused by B. divergens. Babesia species are also found in companion animals including B canis and B gibsonis in dogs, B felis and B cati in cats and B equi and B caballi in horses. b) Tick control Tick control aims are preventing attachment of ticks if possible, and preventing transmission of pathogens by prompt killing or removal. There is usually a delay of several hours after attachment before feeding. Strategies include avoiding tick habitats during late spring and summer, destruction of tick habitats using pesticide sprays, daily inspection of coat and prompt removal and disposal of ticks, and use of repellent or acaricide with a rapid knockdown effect.

Ticks can be removed using tweezers or special tools. It is important to ensure the mouthparts of the tick are removed. The removed tick should be placed in a sealed container, and the area around the bite disinfected. Effective acaricides include fipronil, pyripole, amitraz, deltamethrin, flumethrin, permethrin and imidacloprid. In cattle and sheep dips, sprays, showers and slow-release ear tags of organophosphates, pyrethroids or amitraz can be used. Macocyclic lactones can be given parenterally. Weekly treatment in the tick season is usually effective.

2.5

Mites

Infestation by mites is called acariasis and can often result in severe dermatitis known as mange. The most important conditions caused by mite infection are:







Sarcoptic mage (dogs, pigs) Psoroptic mange (sheep, cattle, camelids, rabbits) Chorioptic mange (horses, cattle) Demodectic mange (dogs) Cheyletiellosis (dogs, cats) Poultry mite (Dermanyssus gallinae) infestation Cnemidocoptic mange (poultry and psittacine birds) Otodectic mange (dogs, cats)

Mites may be burrowing or surface. Burrowing mites include sarcoptes, notoedres, trixicarus, knemidocoptes and demodex. Surface mites include psoroptes, chorioptes, otodectes, cheyletiella, dermanyssus and thrombiculidae. The location of the mite will affect the choice of treatment. The general lifecycle of mites is as follows: Female produces large eggs from which 6-legged larvae hatch. The nymph then moults into 8 legged adult.

Larva moult into 8 legged nymph. There are 1-3 nymphal stages.

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