PA2 Arthropods as Parasites & Vectors (PDF)

E-learning: Arthropods as parasites and vectors. An introduction to arthropods and their biology. Mites. Ticks. Lice. Fleas. Flies. Arthropods as vectors...

E-learning: Arthropods as parasites and vectors. An introduction to arthropods and their biology. Mites. Ticks. Lice. Fleas. Flies. Arthropods as vectors of pathogens.  Learning outcomes: Awareness of the roles of arthropods as veterinary parasites and vectors. Understanding of diverse life cycles and adaptations to parasitic life with reference to achieving parasite control. Some arthropod parasite life cycles and biology are used as examples. They are covered in more detail in other relevant lectures.  What are arthropods? 80% of all known animal species. Invertebrates, with a hard chitinous exoskeleton, a segmented body and jointed limbs. Air breathing and grow by ecdysis. Complex metabolism and Cat flea, Ctenocephalides felis. biochemical pathways and. Question: Why is knowledge of arthropod biology important for control of parasitic diseases? Arthropods are classified as Insecta and Arachnida.  Arthropod biology. Circulatory System - Haemolymph Malpighian tubules - Excretory organs is driven by heart through an open responsible for the removal of metabolic circulatory system. wastes from the haemolymph. Cerebral ganglion - The area in which two nerve chords meet can be regarded as the insect brain and is where sensory organs are concentrated. Mouthparts - Specialised for food source, mandibles in Tracheal tubes - Branched, chitin-lined grasshoppers- in other gas exchange system- opens to the insects can be specialised for outer environment through spiracles lapping, sucking or piercing. which regulate osmolarity and gas exchange through opening and closing. Abdomen. Thorax. Head.  Insecta. Fly 3 pairs of legs in adults. Distinct head, thorax and abdomen in adults. A single pair of antennae in adults. Life cycles with partial or complete Flea Louse metamorphosis. Question: How does this information aid in the diagnosis of parasitic diseases?  Arachnida. Mite 4 pairs of legs in nymphs and adults. Mouthparts and a fused cephalothorax and abdomen. No antennae. Question: How does this information aid in the diagnosis of parasitic diseases? Tick  Insect life cycles – partial metamorphosis. Juvenile stages broadly resemble adults. Juveniles are referred to as nymphs. A new cuticle is made and the old cuticle shed at 4 or 5 intervals throughout Example: the human head louse, Pediculus humanis capitus. development. At each stage, the insect increases in size.  Life cycle of the human head louse, Pediculus Adult humanis capitus. Egg, Adult females attach cemented to eggs to hairs. a hair shaft Sexual reproduction Nymphs hatch in adults. from eggs. Life cycle is completed Example: Anoplura (blood sucking lice). in about 2 weeks. partial metamorphosis. Nymphs moult three times before becoming sexually-mature adults.. Nits Insect life cycles – complete metamorphosis. – Juvenile and adult stages are dissimilar. – Juveniles are referred to as larvae, moggots or grubs. – Juveniles adapted for feeding and growth. Fly example: Culex mosquito. – Adults adapted for reproduction and dispersal. – Reorganisation and reconstruction of the entire body during metamorphosis within the pupa stage. Flea example: Spilopsyllus cuniculi.  Life cycle of the cat flea. Females lay eggs continuously. Example: Adults of both sexes remain on the host complete Eggs and faeces of adults, containing and feed repeatedly. metamorphosis. blood drop into the environment. Undigested blood in fl faeces in cat fur. Larvae feed on part Flea larva. digested blood in adult faeces. The transition from larva to pupa to adult is a complete metamorphosis.  Life cycle of the house fly. Eggs are laid in the environment, for example in rotting organic material or dung. Adults are parasitic, with sponging mouthparts. Example: complete metamorphosis. Three larval stages are free living, feeding on rotting organic material. Larvae (maggots) pupate in the same environment.  Arachnida life cycles – partial metamorphosis. Four basic stages (egg, 6-legged larva, 8- legged nymph and 8- legged adult. – (Further division in some genera into pre- larva, larva, protonymph, deutonymph, tritonymph and adult.) Moulting between stages. Mite example: Sarcoptes scabiei. Question: what are the implications of different arthropod life cycles in their control?  Three host tick life cycle. Adult females drop to the Larvae hatch and then ground and lay eggs. feed on a host. Adults feed and Larvae drop to the ground mate on a host. and moult to nymphs. Nymphs feed on a host. Nymphs drop to the ground and moult to adults.  Arthropod parasite reproductive strategies. Life cycles and reproductive strategies of most (not all) arthropod parasites enable advantage to be taken of favourable conditions, often leading to rapid population expansion. Survival during adverse conditions as or moulting, pupating, or pharate stages. Rhipicephalus (Boophilus) microplus ticks produce large numbers of More detail on parasitic adaptations is offspring in order to sustain their population size. provided in the descriptions of specific parasites and diseases.  Adult arthropod parasite biology. The chitinous exoskeleton protects from desiccation, Most (not all) mites are small and susceptible to desiccation, hence pathogens and predators. adapted to be permanently parasitic. Most are ectoparasites. A few are endoparasites. Ticks survive desiccation off their hosts for long periods of time, provided that a suitable habitat is available, hence are adapted to be temporarily parasitic.  Adult arthropod parasite biology. Some are permanently parasitic – eg. keds and mange mites. Example: mange mites. Example: the sheep ked, Melophagus ovinus.  Life cycle of the sheep ked, Melophagus ovinus. Females produce larvae that adhere to the wool and pupate immediately. Example: Permanent parasitism. Adults are about 5 mm long, wingless flies, with flattened bodies, strong legs and claws. These are adaptations for Adults emerge permanent parasitism. after ~3weeks  Adult arthropod parasite biology. Some are temporarily parasitic, only visiting hosts for a blood meal, – eg. midges and poultry red mites. Example: Culicoides midge. Dermanyssus gallinae poultry red mites on a water trough. Example: Dermanysus mite. Life cycle of the poultry red mite, Dermanyssus gallinae. Eggs. Adults. Example: Temporary Larvae. parasitism. Adults and nymphs ‘attack’ Deutonymph. birds at night to feed on blood. Protonymph. Fed. Most time is spent away from avian hosts in dark cracks or crevices in housing or in nests. Pre-feed. Adult arthropod parasite biology. Some are parasitic as developing stages, but not as adults. – eg. myiasis flies and Blow flies are parasitic as larvae harvest mites. (maggots), but not as adults. Trombicula autumnalis harvest mites are parasitic as 3-legged larvae, having blood sucking mouthparts, but not as nymphs or adults.  Life cycle of the harvest mite, Trombicula autumnalis. Blood in gut. Eggs. 6-legged larvae. Example: Parasitism only as developing stages. 8-legged adults. Nymphs and 8-legged adults are nymphs. Blood feeding free-living. mouthparts.  Life cycle of sheep blow flies. Eggs are laid on the skin surface of live animals (or on carrion, or rotting organic material). The three larval stages (maggots) are adapted to feed on Example: living subcutaneous Parasitism only as tissue. developing stages. Adult are not adapted for parasitism. 3rd stage larvae drop to the ground and larvae pupate in the environment.  Insect larvae. Fly larvae are voracious feeders to provide enough food for the adults to survive until their first feed, or to support reproduction. Some fly larvae are parasitic, eg. myiasis fly Hypoderma diana deer warble fly larvae are large, with sufficient energy larvae, while the adults reserves to support non-feeding adults. are not. Question: what are the implications of different arthropod adaptations in their control?  Arachnid larvae. Ticks and most (not all) mites are parasitic in all stages. Mange mites are permanently parasitic. Ixodes ricinus tick larva using sensory organs on the front legs to detect a host. Question: what are the implications of different arthropod adaptations in their control?  Parasitic adaptations for feeding. Mouthparts adapted for chewing at skin scales and hair. – Strong mandibles acting like a pair of jaws. eg. chewing lice. Columbicola columbae (pigeon feather louse). Trichodectes canis (dog chewing louse).  Parasitic adaptations for feeding. Mouthparts adapted for tearing host tissue. – Large, strong, curved hooks. eg. myiasis fly larvae. Mouth hooks on dipteran fly larvae (maggots).  Parasitic adaptations for feeding. Tabanid horse fly (cleg). Insect blood feeding mouthparts. – Cutting and slashing. eg. midges and tabanids. – Hypodermic tubes. eg. mosquitos, stable flies and sucking lice. Question: How do the different mouthparts determine the nature of the harm or disease caused? Stomoxys calcitrans stable fly. Slashing and sponging mouthparts of a female tabanid fly. Antennae. You should not attempt to memorise the names of the specific mouthparts. Labrum. Mandibles. Hypopharynx. Maxillae. Labella. You should understand that the mouthparts are short and powerful, adapted to create a wound from which blood or fluid is then sponged and aspirated.  Hypodermic sucking mouthparts of a mosquito. Antennae. Mandibles. Hypopharynx. Maxillae. Labium. Labrum. You should understand that the mouthparts consist of a conspicuous, You should not attempt to memorise the names of forward-projecting, elongated proboscis, adapted for piercing and sucking. the specific mouthparts.  Piercing and sucking mouthparts of the stable fly. Arista. Antenna. You should understand that the stable fly has a conspicuous, forward- Labium. projecting proboscis, adapted for piercing the Labrum. skin and sucking blood. You should not attempt to the specific mouthparts. memorise the names of The proboscis swings Hypopharynx. downwards when feeding and the skin is pierced by the rasping action of teeth Labella with teeth. at the end of the labium.  Parasitic adaptations for feeding. Sponging mouthparts. – Act like a sponge for secretions at mucous membranes, or blood. eg. house flies, face flies, head flies, horn flies and clegs. Musca autumnalis face flies. More detail on feeding mechanisms is provided in the descriptions of specific parasites and diseases. Hydrotaea irritans head flies.  Sponging mouthparts of the house fly. Antenna. Palps. Labrum. You should understand that the complex mouthparts are adapted for sponging, and are only Labella. extended during feeding. You should not attempt to memorise the names of the specific mouthparts.  Parasitic adaptations for feeding. Mite and tick blood feeding mouthparts. – Jaw-like chelicerae incise the epidermis. – Hypostome for blood feeding. – Together these structures form a stout, barbed tube. Ixodes ricinus tick.  Ixodes ricinus Tick mouthparts. Mandibular digits. Mandiblar shaft. Mandibular Hypostome. sheath. Palp. You should understand the manner in which the jaw-like chelicerae (mandibles) incise the epidermis, creating an opening for the soft hypostome to be inserted into. The hypostome is rolled into a blood feeding tube. You should also be able to recognise Basis capituli. these mouthparts as being those of a tick. Parasitic adaptations for feeding.  Other adaptations for parasitic behaviour. Temporary parasites find their hosts using antennae, wings, eyes, powerful legs, etc.. Temporary parasites may feed rapidly, adhere strongly, or secrete anaesthetic substances to avoid being removed by Fleas are highly adapted to identify, their host. attach to and feed from their hosts. More detail on parasitic adaptations is provided in the descriptions of specific parasites and diseases.  Other adaptations for parasitic behaviour. Permanent Fleas have flattened bodies to move parasites remain on between dense fur or hair coats and rows of their hosts using combes to avoid becoming dethatched. hooks, combs, body Sarcoptes scabiei are permanently parasitic and scales, etc.. adapted to live in the stratum corneum. They have a large surface to volume ratio, hence do not survive for Parasites body more than a few days away from their host. shapes are adapted to suit their niche on the host. More detail on parasitic adaptations is provided in the descriptions of specific parasites and diseases.  Arthropods as transmitters of pathogens. Mechanical transmission. – No involvement of the pathogens with the life cycle of the parasite vector, or development within the vector. eg. summer mastitis, keratoconjunctivitis and Female flies take several meals for each tick pyaemia. batch of eggs, enabling transmission of pathogens on their mouthparts. More detail on arthropods as vectors is provided in the descriptions of specific parasites and diseases.  Arthropods as transmitters of pathogens. Biological transmission. – Transfer of pathogens from one vertebrate host to another during blood feeding. – The pathogen must survive within the transmitter and move from the gut to the mouthparts before it can be transmitted to another More detail on arthropods as vectors is provided in the descriptions of specific host. parasites and diseases.  Trans-statial biological transmission of Three host ticks feed once as larvae, nymphs and pathogens by ticks. adults. Each stage feeds on a different host. Pathogens survive moulting. Pathogens must move from the tick gut to its salivary glands before transmission to the next host.  Arthropods as transmitters of pathogens. Biological transmission. – Survival and replication within the vector is often an important part of the pathogen’s life cycle. eg. bluetongue, African horse sickness, tick borne fever and babesiosis. More detail on arthropods as vectors is provided in the descriptions of specific parasites and diseases.  Biological transmission of pathogens by flies. Example: Culex mosquitos and West Nile Virus. Transmission by one female during feeds for repeated egg laying. Mosquitos become infected by biting wild birds that carry the virus. Rapid viral multiplication in Slow viral birds – amplification hosts. multiplication in horses and man – dead end hosts.