ENTO 301 – MEDICAL & VETERINARY ENTOMOLOGY (Lectures 1-5)

1. ENTO 301 –MEDICAL & VETERINARY ENTOMOLOGY(Lectures 1-5) Dr Terry Olckers School of Biological & Conservation Sciences

2. Introduction • Insects have huge impact on health of humans & domestic animals • Irritation & diseases • Relatively few species involved but serious social & economic consequences • Transmit diseases (vectors) • Inject venoms & transmit allergens • Cause wounds • Create nuisance & phobias • Other arthropod groups also very important Leishmaniasis Myiasis

3. Introduction • Major insect orders • Diptera (flies) • Hemiptera (true bugs) • Phthiraptera (lice) • Siphonaptera (fleas) • Diseases & causative pathogens • Other arthropod groups • Acari (ticks & mites) • Araneae (spiders) • Scorpiones (scorpions) Protozoan causing sleeping sickness

4. Nuisance & phobias • Nuisance mostly related to high densities & not real hazards • Justified in case of biting, venomous & filth-frequenting species • Major causes of nuisance & irritation • Blood-feeding species • Lachrymal-feeders • Immunological reactions • Phobic responses (delusory parasitosis) • Large industries are focused on pest control Mosquito feeding frenzy

5. Blood-feeding species • Cause major annoyance & impacts • Humans: reduce tourism, outdoor activities, land development & land values • Domestic livestock: death via major blood loss; increases stress & grooming activities; lowers agricultural production • Main culprits = flies, fleas, lice, bugs, ticks, mites Mosquito Bed bugs

6. Immunological reactions • Caused by antigens in saliva of ectoparasites • Long-term exposure to bites may lead to no skin reactions • Host’s immune defences may be neutralized (immunosuppresion) • Saliva contains additives to aid feeding & pathogen transmission [immunosuppressants + anticoagulants + vasodilators + pain inhibitors] • Immunosuppressants inhibit production of macrophage molecules that kill pathogens Allergic reaction to flea bite

7. Phobic responses • Some organisms cause fear & panic in humans (snakes, spiders, insects) • Delusory parasitosis (entomophobia) • Persistent bites & skin rashes has psychological origin • Obsessive-compulsive disorder = sensation of insects crawling, biting & burrowing into skin • Sensation causes chronic itching & mental anguish & self-abuse

8. Delusory parasitosis • Sufferers seem normal & condition is difficult to diagnose • Symptoms mimicked by several conditions • Food & skin allergies, drug abuse & medical conditions like diabetes, hepatitis etc • Infestations of parasitic insects or microscopic mites • Condition may have genetic basis & could be drug induced • Treatment usually with drugs Symptoms can be confused with skin allergies

9. Insect venoms • Best known are social Hymenoptera • Bees, wasps & ants sting in defence of nests • Venom delivered via modified ovipositor • Honey-bee stings are barbed & used once (sting + venom sac remain in wound) • Wasp & ant stings are smooth & used repeatedly • Some ants have reduced stings & spray venom into wound • Reactions to venom • Dermatitis • Severe neurological & cytological symptoms • Localized or systemic allergic reactions • Secondary bacterial infections

10. Reactions to venom • Mostly local inflammatory response • Systemic allergic reactions after several exposures (hypersensitivity) • Release of histamine leads to dilation of blood vessels • Effects include allergic responses, tissue swelling & respiratory problems • Immediate hypersensitivity (anaphylaxis) can be fatal Local response from wasp sting Systemic response from fire ants

11. Toxicity & fatalities • Most fatalities caused by honey bees • Shock from multiple stings • Allergic response (anaphylaxis) from single sting • In non-sensitized people, LD50 varies • 500 stings for children • 1100 for adult females • 1400 for adult males • Allergic people must avoid allergens & carry medication

12. Other insect toxins • Not all toxins inoculated via stings • Physical contact with body parts, haemolymph, poisonous spines & defensive secretions • Blister beetles (Meloidae) release toxins (cantharidins) when crushed or handled • Cause blistering of skin • Cause inflammation of urinary & genital tracts if taken orally (aphrodisiac ‘Spanish fly’) Skin blistering Blister beetle

13. Other insect toxins Paederus beetle • Body fluids of other beetles have potent toxins • Certain flea beetles (Chrysomelidae) that feed on toxic plants are used for arrow poisons by San people • Some rove beetles of genus Paederus (Staphylinidae) have contact poisons (paederin) that cause blistering & long-lasting ulceration Ulcers from paederin

14. Urticating hairs • Larvae (also pupae) of some beetles, butterflies & moths • Penetrate skin causing skin irritations (urtication) • Structure & function of hairs • Hollow spines with subcutaneous venom glands • Setae (bristles & hairs) with irritating toxins • Retain irritant properties long after being shed • Intense burning sensation on skin • Breathing difficulties if inhaled • Inflammation of mouth & throat if ingested Lonomia achelous

15. Venoms & discomfort levels • Death in extreme cases • Mostly due to hypersensitivity & anaphylaxis • Discomfort (pain) lasts for variable periods • Few hours if Hymenopteran stings • Few days if urtication • Few weeks if ulcerated blisters Anaphylaxis = most serious outcome

16. Arthropod allergens • Repeated exposure to allergens (mostly proteins) causes excessive immunological reactions • Many allergens are airborne & cause respiratory problems • Allergens found in shed cuticle, faeces, saliva & dead bodies • Entomologists may develop allergic reactions (rhinitis, asthma) • Wide diversity of arthropods implicated • Insect cultures (e.g. mealworms, bloodworms, cockroaches etc) • Mites in stored products cause ‘baker’s itch’ or ‘grocer’s itch’ • House-dust mites cause house-dust allergy House-dust allergy is most widespread

17. Arthropods & disease • In tropics & subtropics, many arthropod-transmitted pathogens cause disease • Protozoa, bacteria, viruses & nematodes • Arthropods may be causative agent • Human lice cause pediculosis • Skin-burrowing mites cause scabies • Fly maggots invade living flesh (as primary or secondary agents) & cause myiasis Protozoa causing malaria Scabies caused by mites

18. Transfer of pathogens • Mechanical transfer • Occurs passively & externally from host to host • Pathogen does not increase inside vector • House flies & cockroaches transfer bacteria from faeces to human food (on mouthparts, legs & body) • Arthropods are one of several means; poor public & personal hygiene are main pathways Musca domestica

19. Transfer of pathogens • Biological transfer • Specific association between vector, pathogen & host • All 3 components essential • Pathogen increases inside vector (close specificity between them) • Arthropod is vital link in disease transmission Malaria cycle

20. Disease control • Combination of 3 approaches • Reduce vector numbers in field (spraying programmes) • Disrupt contact between vector & host (pesticides & repellents) • Attack pathogen inside host (prophylactic drugs) • Development of vaccines? • Requires detailed knowledge of biology of vector, pathogen & host (research)

21. General disease cycles • Biologically transferred diseases • Blood-feeding adult arthropods transmit parasites • Animal to animal • Human to human • Animal to human • Human to animal (very rare) • Human diseases have single or secondary cycles

22. Single cycles • Pathogen completes life cycle only within vector & human host • Human malaria (parasite needs Anopheles mosquitoes & humans) • Similar malaria parasites infect primates & birds but don’t affect human malaria cycle • Few human diseases with single cycles • Need coevolution of vector, pathogen & man • Man is of recent evolutionary origin; short time for evolution of unique insect-borne diseases that rely on man Anopheles

23. Secondary cycles • Pathogen completes life cycle within vector & animal or human host • Non-human vertebrates are primary hosts • Monkeys (yellow fever); rats (plague); desert rodents (leishmaniasis) etc • Animal diseases that affect man = zoonoses • Human inclusion in cycle is not essential to maintain disease & animals act as disease reservoirs • Outbreaks occurs when humans spread into natural ranges of vectors & disease reservoirs

24. Secondary cycles: yellow fever • In Ugandan forests, disease has sylvan (woodland) cycle • Reservoir = canopy-dwelling primates • Vector = primate-feeding mosquito (Aedes africanus) • Humans & monkeys coincide at banana plantations near forest • Second vector (Aedes bromeliae) that feeds on both humans & monkeys transmits virus to humans

25. Secondary cycles: leishmaniasis • In Arabia, sand flies feed on burrowing rodents & transmit protozoan parasites • Disease affects humans when suburban expansion overlaps with rodent reservoir • No change in vector when humans enter cycle • Animal reservoirs maintain natural disease cycles & complicate control

26. Disease outbreaks • Epidemics = outbreaks in human populations • Epizootics = outbreaks in animal populations • Pandemic = worldwide epidemic

27. Pathogens & transmission • Pathogens transferred by arthropods • Viruses (arboviruses) • Bacteria (also rickettsias) • Protozoan parasites • Filarial nematode worms • Need to replicate in vectors & hosts → complex life cycles • Parasites generally don’t harm vectors • Pathogen presence determined by • Dissection & microscopy • Biochemical means Filarial nematodes West Nile virus

28. Pathogens & transmission • Pathogens transferred during infective stage & after replication in vectors • Transfer from vector to host (or vice versa) occurs when blood-feeding arthropod feeds on vertebrate host • From host to uninfected vector via parasite-infected blood • From infected vector to host via injection with anticoagulants that keep wound open during feeding • Transfer may also be via deposition of infected faeces close to wound (gets rubbed in) Blood-feeding Infected faeces

29. Major insect groups • Most important taxa • Order Diptera (flies) – 11 families • Order Hemiptera (true bugs) – 2 families • Order Phthiraptera (lice) – 4 families • Order Siphonaptera (fleas) – 2 families • Aspects considered • Key taxonomic features to aid identification • General biology & life history

30. Diptera (flies) • Large well-known group • Thousands of important species • Adult features • 1 pair of membranous fore-wings • Hind wings reduced to form halteres • Mouth parts are proboscus-like for sucking fluids or piercing & sucking for penetrating tissues • Larval features • No conspicuous head • Legless • Slender bodies with pointed fronts which broaden towards rear Fluid sucking Piercing

31. Culicidae (mosquitoes) • Transmit several parasites • Protozoa (malaria) • Filarial worms (elephantiasis) • Arboviruses (yellow fever, dengue fever, encephalitis) • Identification • Long & narrow wings with scales along veins & wing margin

32. Culicidae (mosquitoes) • Biology • Almost all blood-sucking; only females take blood; males take nectar & plant juices • Eggs laid in flowing or still water; water collected in containers, tree cavities & leaf axils of plants • Eggs laid singly or together in floating raft • Larvae & pupae are aquatic; active swimmers & breathe via siphon tube • Adults usually close to breeding sites Blood-feeding females Aquatic larva

33. Culicidae (mosquitoes) Eggs • 2 subfamilies • Anophelinae • Genus Anopheles (human malaria) • Adults rest with abdomen tilted at steep angle to substrate • Larvae rest horizontally on water surface • Culicinae • Genera Aedes & Culex (arboviruses & filarial worms) • Adults rest with abdomen parallel to substrate • Larvae hang at angle from water surface Egg raft Larvae Pupae Adults

34. Simuliidae (black flies) • Females are blood-feeders • Vicious biters & cause major distress to poultry, livestock & humans • Cause extreme pain, itching & local tissue swelling • Vast swarms cause livestock deaths via blood loss, suffocation & trauma • In tropical Africa, Simulium damnosum transmit filarial worms that cause river blindness in humans • Also transmit filarial worms, trypanosomes & Leucocytozon disease in poultry

35. Simuliidae (black flies) • Identification • Small (2-5 mm) stocky grey-black flies • Humped thorax (buffalo gnats) • Clear wings without hairs or scales • In SA most belong to genus Simulium; S.damnosum occurs but not disease

36. Simuliidae (black flies) • Biology • Aquatic larvae live in fastest flowing parts of streams & rivers • Larvae attach to rocks & vegetation (via silk & hooks) • Larvae are filter-feeders using complex labral fans on head • Pupate on rocks underwater • Adults may occur several km from water Aquatic larva Head fans

37. Psychodidae (moth flies, sand flies) • Mostly harmless, except blood-sucking sand flies (subfamily Phlebotominae) • Transmit several pathogens • Protozoa (leishmaniasis) • Arboviruses (pappataci fever) • Bacteria (oroya fever) • Identification • Small cryptic flies (2-4 mm) • Very broad & hairy wings with long parallel veins • Wings held open over body

38. Psychodidae (sand flies) • Biology • Adults hide in hyrax & rat burrows during day; enter houses at night to feed • Adults & larvae live near water • Larvae live in moist soil or in cracks & crevices where they survive on condensed water

39. Ceratopogonidae (biting midges) Females of some genera (Culicoides) are blood-suckers; males visit flowers • Painless bite is followed by intense irritation & itchiness • Identification • Very small flies (0.5-2mm) • Grey or yellowish bodies • Wings folded over body at rest • Wings have thick radial veins crowded close to wing margin

40. Ceratopogonidae (biting midges) • Biology • Larvae carnivores or detritivores • Larvae mostly live in water bodies with high organic content; some live in moist or terrestrial habitats • Adult females transmit arboviruses in livestock • Bluetongue virus in sheep • African horse sickness • Species that bite humans may transmit filarial worms & viruses Infestation of Culicoides

41. Tabanidae (horse flies) • Females are voracious blood-feeders • Serious pests of livestock (suffer weight loss) • Also bite humans • Transmit several parasites • Protozoa → surra (cattle, horses, camels) • Bacteria → tularaemia & anthrax (humans) • Filarial worms → loiasis (humans)

42. Tabanidae (horse flies) • Identification • Large, stoutly built flies • Often have irridescent eyes • Antennae have 3 segments; 3rd segment is elongated & annulated • Wings have large calypters • Wing veins diverge at wing tip to form an open ‘V’

43. Tabanidae (horse flies) • Biology • Adults feed on nectar & plant juices; females take vertebrate blood • Larvae develop in moist habitats, often in mud at edges of water bodies • Most larvae feed on decaying plant matter; some are predaceous

44. Glossinidae (tsetse flies) • Single genus (Glossina) • 29 species & subspecies groups = 3 ‘species groups’ • Both sexes are host-specific blood-suckers (bites are painful) • Transmit protozoans (trypanosomes) • Sleeping sickness (humans) • Nagana (livestock) Tsetse bite

45. Glossinidae (tsetse flies) • Identification • Medium sized flies with very tough & leathery body (survive swatting) • Flattened body & short forward-pointing proboscus • Wings folded scissor-like at rest; conceal abdomen • Wings have ‘hatchet cells’ Hatchet cell

46. Glossinidae (tsetse flies) • Biology • Adults active during day • Occupy habitats with trees (e.g. grasslands & woodlands) • Both sexes feed on large mammals; humans only attacked in absence of game • Females incubate single maggot in their bodies • Nourished by ‘milk gland’ • Larvae pupate in soil; very soon after deposited Typical tsetse habitat

47. Muscidae (house flies) • Large group with many common flies & some important pests • Nuisance flies • Mechanical disease transmitters • Identification • Thorax lightly striped • Mostly based on prescence or absence of bristles on thorax • Biology • Larvae live in various types of organic matter; manure, garbage, rotting vegetation • 2 important subfamilies • Muscinae • Stomoxyinae

48. Muscidae (house flies) • Muscinae • Non-biting species – short fleshy proboscus for mopping up surface liquids • Some species extract fluids from human food & faeces (e.g. house fly, Musca domestica) • Such species mechanically transfer bacteria & viruses • Cholera, poliomyelitis, leprosy, typhoid fever, dysentery etc • Others feed on wounds or run off from wounds • Some involved in myiasis

49. Muscidae (house flies) • Stomoxyinae • Biting species – long piercing mouth parts • Some species are aggressive & persistent blood-suckers (e.g. stable fly, Stomoxys calcitrans) • Torment wild & domestic animals (e.g. ears of dogs) Stomoxys calcitrans

50. Calliphoridae (blow flies) • Identification • Stoutly built flies • Shiny metallic (blue or green) colour • Plumose arista (at least 2/3 of length) • 2-3 notopleural bristles