Parasitic arthropods IParasitic arthropods IArthropods as parasites in their own right.

Dr. Jo HamiltonParasitology BS

Introduction. Introduction.

Parasitic arthropods can be considered as ectoparasites in their own right & some arthropods have capacity to become vectors of viral, bacterial, protozoal & helminth diseases.

During the next two lectures we will investigate both of these roles of parasitic arthropods.

In this first lecture we will consider parasitic arthropods as ectoparasites and/or micropredators in their own right and in the second lecture in this series we will explore parasitic arthropods as vectors of disease.

Objectives and learning outcomes. Objectives and learning outcomes.

By the end of this session students should be able to:

Appreciate that parasitic arthropods can be parasites in their own right, or vectors of disease.

Describe the main classes of parasitic arthropods. Give named examples from these classes. Appreciate the economic importance and the

implications for public health of parasitic arthropods.

Arthropods.Arthropods. Arthropoda (Arthropod = "joint-footed") are an

enormous phylum.

Most successful life-form on Earth in terms of variety.

Over 1 million known species. Probably 10x as many unidentified species.

Arthropod success.Arthropod success. Versatile exoskeleton: highly protective and mobile; prevents

dehydration. Segmentation & tagmosis: more efficient locomotion,

feeding, sexual reproduction. Cells directly ventilated in land arthropods (tracheal system). Highly developed sensory organs. Complex behaviour and evolution of social systems. Ecological separation of life stages-reduced competition via

metamorphosis. Exploit a wide range of ecological niches. Not surprising that many groups have evolved & exploited

the parasitic lifestyle.

Arthropod taxonomy.Arthropod taxonomy.Arthropods divided into four sub-phyla: Chelicerata, Hexapoda, Crustacea & Myriapoda.

3 of the 4 groups include parasitic taxa.

In Hexapoda, all parasites belong to class Insecta (insects e.g. flies, bugs, lice and fleas).

In Chelicerata, all parasites belong to Acari (e.g. mites & ticks)

In Crustacea, parasitism has evolved in many different classes (e.g. copepods and decapods).

Parasitic arthropods as parasites Parasitic arthropods as parasites and/or micropredators.and/or micropredators. Blood-sucking micropredators take small amounts of

blood from many hosts.

Do not stay on one host for entire life. Examples include: bed bugs, fleas, mosquitoes, tsetse flies & black flies etc.

Micropredators have some general characteristics in common that have allowed them to evolve this lifestyle.

Parasitic arthropods as parasites Parasitic arthropods as parasites and/or micropredators.and/or micropredators.Micropredators - general common characteristics

allowing exploitation of lifestyle. Specialized to find capillary. Specialized mouthparts to obtain fluids - blood or

lymph. Secrete anti-coagulants in saliva to prevent host

blood clotting. Some secrete anaesthetic in saliva to reduce pain. Many are important intermediate hosts and/or

vectors of infectious diseases (we will discuss this in the next lecture).

Parasitic arthropods.Parasitic arthropods.We will deal main classes of parasitic arthropods in

turn, Insecta, Arachnida & Crustacea.

1. Class Insecta.

Amongst the insects, the fleas, flies, hemipterans hymentopterans & lice have parasitic species.

We will deal with fleas, flies, hemipterans & lice in this lecture. We will only deal with those species of medical or veterinary importance, further details of other species can be found in the lecture notes.

Parasitic insects - fleas.Parasitic insects - fleas.

Class Insecta. Order Siphonaptera – the fleas.

~ 2000 species of fleas, grouped into 15 families.

94% of extant flea species parasitize mammals, 6% parasitize birds.

Gross morphology similar in all fleas.

Parasitic insects -fleas.Parasitic insects -fleas.

Fleas have some interesting morphological adaptations to the parasitic life style:

Body laterally compressed. Mouthparts modified for piercing/sucking. Presence of ctenidia (sing. ctenidium) or

combs. Presence of pygidium. Legs modified for running & getting on and

off host. Gut modifications.

Parasitic insects - fleas.Parasitic insects - fleas.

Most fleas locate host by CO2, specific odours, light/dark contrast, vibrations, & air currents.

Host specificity varies & many species can move between different host species.

This increases the vector potential of these species (we will discuss vectors in the next lecture).

Some fleas are very specific, e.g. rabbit fleas. Some female fleas attach permanently as adults,

e.g. "sticktight flea", Echidnophaga gallinacea. Most other species only spend a proportion of their time on the host.

Parasitic arthropods - fleas.Parasitic arthropods - fleas.

The "chigoe" flea, Tunga penetrans, is highly modified & the female attaches permanently.

Feeding induces host tissue to swell around flea body (they don't burrow as used to be thought).

Body volume increases up to 1000 times. This flea exhibits neosomy, the ability to produce

new cuticle without moulting. T. penetrans shows little host specificity and readily

attacks humans. T. monositus, a related species parasitizes rodents, &

produces very large eggs. Neither larvae nor males of this species feed.

Parasitic insects - fleas.Parasitic insects - fleas. The dog flea (Ctenocephalides canis), cat flea,

(C. felis), sticktight flea (Echidnophaga gallinacean), the human flea (Pulex irritans), and other species may be found on our pets.

Most species are quite active & move through the hair rapidly when disturbed (exception of the sticktight flea).

Parasitic insects - fleas.Parasitic insects - fleas.Consequences of flea infestation: Irritation. Animals, particularly cats (& humans),

may develop a sensitivity to flea saliva, causing an allergic skin reaction (skin eruptions). Scratching due to allergy at bite site may lead to skin damage & secondary (e.g. bacterial) infections of damaged skin.

Blood feeding may lead to anaemia particularly in young, old or sick animals. High population density in some bird nests may lead to mortality.

Tissue damage. Subcutaneous fleas such as Tunga can cause serious damage. Severe pain results from necrosis of host tissue.

Parasitic insects - fleas.Parasitic insects - fleas.Consequences of flea infestation cont’d: Fleas can act as vectors of disease and may

transmit bacterial, viral and protozoan diseases and tapeworms (we will discuss this in the next lecture).

Parasitic insects - fleas.Parasitic insects - fleas.Economic importance of flea infestations. The Siphonaptera includes medically important

species e.g. Tunga and Pulex irritans. Generally fleas are a nuisance for man as they are

most commonly encountered through our pets and can infest our homes.

Large market for flea control products for companion and domestic animals.

Also of veterinary importance – mainly in companion animals & poultry. Heavy infestations can lead to economic loss in poultry farms.

Parasitic insects - flies.Parasitic insects - flies.

Class Insecta. Order Diptera – the true flies.

127 families of Diptera, over 85,000 named species.

Diptera contains greatest diversity of parasitic insects & different types of parasitism have evolved in numerous independent lineages.

Diptera important because contains the most important vectors of human disease (we will describe dipteran vectors in the next lecture).

Parasitic insects - flies.Parasitic insects - flies.Diptera display different types of parasitic life style. Adults, temporary ectoparasites of vertebrates or

invertebrates; larvae are free living. e.g. mosquitoes, black flies, deer flies.

Adults, permanent ectoparasites of vertebrates or rarely invertebrates; free living or non-feeding larvae. e.g. louse-flies, bat flies.

Larvae, ectoparasites of vertebrates; adults free-living. e.g. screw worms.

Larvae, endoparasites of vertebrates; adults typically non-feeding. e.g. botflies, warble flies.

Larvae, parasitoids of invertebrates; adults free-living. Many examples of hymenopterans. 

Parasitic insects - flies.Parasitic insects - flies.

Dipteran taxonomy can be confusing (see lecture notes for further information).

In this lecture we will consider some of the families of flies of medical and veterinary importance.

Further information can be found in the lecture notes.

Parasitic insects – Parasitic insects – Black flies.Black flies.Order Diptera. Suborder Nematocera. Family

Simuliidae - the "black flies". ~ 1,600 named species - worldwide distribution.

Adult females obligate temporary ectoparasites, blood feeders of vertebrates, mostly birds but some mammals.

Host specificity not particularly pronounced.

Parasitic insects – Parasitic insects – Black flies.Black flies.Effects on hosts. Allergic reactions. "Blackfly fever" - Numerous

bites induce headache, fever, nausea, swollen lymph nodes, depression. Common in eastern Canada and northeastern USA.

Vectors of Onchocerca volvulus, a filiarial nematode.

Vectors of Leucocytozoon spp., protozoans causing "malaria" in birds.

Role of black flies as vectors will be discussed in the following lecture.

Parasitic insects – Parasitic insects – midges.midges.Order Diptera. Suborder Nematocera.

Family Ceratopogonidae - biting midges. Very small - 0.6 - 5mm. Large family, poorly known. Adult females all temporary parasites, most

on other insects, a few parasitize vertebrates.

Bites are painful. Most species which bite vertebrates are in

the genus Culicoides.

Parasitic insects – Parasitic insects – midges.midges.Effects on vertebrate hosts: Annoyance problems & vectors of other

pathogens/parasites. Culicoides species are vectors of

Acanthocheilonema perstans, a filarial parasitic nematode of humans and also vectors of other filarial nematode parasites of domestic livestock.

Vectors of malaria-like species in the genera Hepatocystis in birds and mammals, & Akiba in birds.

Parasitic insects – Parasitic insects – mosquitoes.mosquitoes.Order Diptera. Suborder Nematocera. Family

Culicidae - the mosquitoes. ~ 3,500 species & subspecies worldwide. Most important family of human disease vectors

(see next lecture for details). Adult females in most species are temporary

blood-feeding ectoparasites of vertebrates, few parasitize invertebrates, some non-parasitic; males of all species & females of some primitive taxa are non-parasitic plant feeders.

Parasitic insects – Parasitic insects – mosquitoes.mosquitoes.

Order Diptera. Suborder Nematocera. Family Culicidae - the mosquitoes.

Most females require blood meal to mature eggs; some mosquitoes are autogenous.

Host specificity is variable; feed on all groups of terrestrial vertebrates (& mudskippers).

Parasitic insects – Parasitic insects – mosquitoes.mosquitoes.Subfamily Anophelinae.

Genus Anopheles (422 species). Recognized by long maxillary palps in both sexes. Eggs laid singly on water surface; larvae without

respiratory siphon. e.g. Anopheles quadrimaculatus, common North

American pest species; Anopheles gambiae, one of most important vectors of malaria in Africa (see following lecture).

Parasitic insects - mosquitoes.Parasitic insects - mosquitoes.Subfamily Culicinae. Short maxillary palps in female (still long in male); eggs

laid singly or in clusters (rafts) on water surface; larvae with respiratory siphon.

Important genera include: Aedes - (962 species) containing notorious pest & vector

species, especially in northern latitudes. Females bite during daylight. e.g. Aedes aegypti - one of

the most important vectors of human diseases, mainly viruses. Breeds in tree holes & human-created cavities.

Aedes albopictus, the "Asian tiger mosquito" introduced into North America, spread eastern USA.

Parasitic insects - mosquitoes.Parasitic insects - mosquitoes.Subfamily Culicinae cont’d. Culex - (751 species) containing important vector species. Females typically feed at night & lay eggs in rafts. e.g. the

following are important vector species: Culex pipiens, the "house mosquito," very widespread vector species Culex tarsalis, Culex quinquefasciatus, breeding in latrines, cesspits

Culiseta - a small genus of 35 species, breeding in aquatic vegetation. e.g. Culiseta melanura, an important disease vector, feeds mainly on birds but may transmit bird viruses to humans.

The vectorial capacity of these insects will be discussed in the next lecture.

Parasitic insects – Parasitic insects – tabanids.tabanids. Order Diptera. Suborder Brachycera Family

Tabanidae - horseflies, deerflies. ~ 4000 species worldwide. Most females intermittent parasites of terrestrial

vertebrates; males not parasitic; some species strictly plant feeders.

Adults characterized by large, heavy body (6-25mm long); large eyes used to locate hosts visually.

Mouthparts modified from ancestral form: cut large wound. Blood sponged up by enlarged labellum (tip of labium).

Parasitic insects – tabanids.Parasitic insects – tabanids.Important genera: Tabanus (includes large horseflies), some larvae are

predaceous e.g. Chrysops & Hybomitra (deerflies).Impact on host: Blood loss - 50 horseflies feeding on livestock can

remove 1/3 litre of blood per day. Decreased rate of development of host. Disease transmission. Tabanids are mechanical

vectors of important bacterial pathogens such as the agents of anthrax (Bacillus anthracis) and tularemia (Francisella tularensis, see following lecture).

Parasitic insects – Parasitic insects – cyclorrhaphans cyclorrhaphans ..Order Diptera. Infraorder Cyclorrhapha.

Superfamily Carnoidea. Family Muscidae. E.g. Stomoxys calcitrans, the stable fly, &

Hematobia irritans, the horn fly. Both adult males & females are intermittent

parasites of vertebrates. Flies pierce skin, then use labellum to sponge

blood. Bites are painful, but these species are only

known as mechanical disease vectors. Blood loss in domestic animals can be serious.

Parasitic insects - Parasitic insects - cyclorrhaphans cyclorrhaphans ..

Order Diptera. Infraorder Cyclorrhapha. Superfamily Carnoidea. Family Glossinidae, genus Glossina – tsetse fly.

Both females & males intermittent parasites of mammals in sub-saharan Africa.

Most tsetse's parasitize ungulates, but will bite humans.

Tsetse are intermediate hosts & vectors of trypanosome protozoans of the Trypanosoma brucei species complex which cause sleeping sickness in humans and nagana in cattle (we will discuss this in the following lecture).

Parasitic insects - Parasitic insects - cyclorrhaphans cyclorrhaphans ..

Order Diptera. Infraorder Cyclorrhapha. Family Hippoboscidae -the "louse flies."

Include parasites of birds & mammals. Winged species typically non-specific. Some wingless, e.g. Melophagus ovinus, the

sheep ked. This species causes economic damage in that

high population densities may lead to anemia. Puparia glued to host hairs, may mat wool.

Parasitic insects – Parasitic insects – hemipterans.hemipterans.Order Hemiptera - the true bugs. Most taxa are predators or plant feeders, parasitism

of vertebrates evolved in 2 lineages. Mouthparts modified for piercing/sucking. Family Reduviidae. Subfamily Triatominae large (up to 35mm)

obligate blood feeding parasites of vertebrtes, usually mammals.

Restricted to the New World. Species are nidicolous parasites of rodents, marsupials, & often humans.

Parasitic insects – Parasitic insects – hemipterans.hemipterans.

Species in genera Triatoma, Panstrongylus & Rhodnius called "kissing or assassin bugs“. All stages are parasitic, feeding at night, often around the mouth of sleeping humans.

Triatomine bugs important vectors of Trypanosoma cruzi, the agent of "Chagas' Disease" (see next lecture).

Parasitic insects – Parasitic insects – hemipterans.hemipterans.Family Cimicidae - bedbugs. All species obligate blood feeders in all instars- parasites of

bats, birds & humans. Man probably acquired bedbugs while sharing caves with

bats. Species commonly associated with humans: Cimex lectularius in temperate areas, Cimex hemipterus in tropical areas.

They live behind wallboard, wallpaper, in cracks, rarely in beds. Active in predawn hours, biting sleeping hosts. They can feed every few days, but can live 1 1/2 years between meals. Locate host by temperature and CO2 gradients.

Human bedbugs are annoying, but do not transmit any known pathogens.

Parasitic insects – Parasitic insects – lice.lice.

Class Insecta. Order Anoplura – the lice. Family Pediculidae Pediculus humanus corporis (body louse) & P. h. capitis (head

louse) common human ectoparasites. Both sexes feed on blood. Mouthparts adapted for piercing &

sucking. Body louse vector for spirochete Borrelia recurrentis (relapsing

fever) & Rickettsia prowazeki (typhus). Head lice are secondary vectors.

Crushed lice/lice faeces in contact with broken skin leads to transmission of both diseases.

Eggs laid singly & glued to hair. Development to nymph takes 7-11 days.

Parasitic insects.Parasitic insects.Economic impact of haematopahgous insects in general. Losses in milk & meat yields. Damage to skins & hides – leather industry. Effects on wool quality. Losses to draught & pack animals through mortality &

reduced productivity of these animals due to morbidity. Impact on human health and productivity. Vectors of medically and veterinary important diseases –

losses due to morbidity and mortalitiy in both human and animal terms.

Losses to agriculture – ranching – saviour of big game animals??

Parasitic arthropods – Arachnida Parasitic arthropods – Arachnida (mites & ticks).(mites & ticks).

2. Order Acari. All parasitic arachnids belong to the Acari, the

mites & ticks.

Parasitic arthropods – mites.Parasitic arthropods – mites.Superfamily Dermanyssoidea. Family

Dermanyssidae. Vessel feeders. Dermanyssus gallinae - the "chicken mite."

Important parasite of many bird groups. Serious pest of domestic poultry. Will bite humans.

D. hirundinis - the "swallow mite." More host specific - typically found in nests of various swallows - if nests on human habitations, mites may enter and bite.

Parasitic arthropods – mites.Parasitic arthropods – mites.Superfamily Dermanyssoidea. Family

Macronyssidae. Hosts are bats, rodents, birds, snakes & lizards. Genus Ornithonyssus - several important pests: O.

sylviarum, the "Northern fowl mite," and O. bursa, the "tropical fowl mite" very non-specific parasites of birds.

Serious pests of poultry, will bite humans. O. bacoti, the "tropical rat mite" normally bites

rodents, including Rattus & Mus, will bite humans. Vector of pathogens among rodents, not to humans.

Parasitic arthropods – Parasitic arthropods – mites.mites.Family Trombiculidae - chiggers - parasites of

terrestrial vertebrates (don’t confuse with chigoe flea).

Host specificity variable. Chiggers can cause dermatitis & can serve as

vectors of "scrub typhus" – a zoonotic disease of humans in Asia, Australia (more next session).

Turkey chigger causes skin and feather problems rendering birds unfit for market.

Chiggers can be responsible for equine mange-like dermatitis.

Parasitic arthropods – mites.Parasitic arthropods – mites.Suborder Sarcoptiformes Family Psoroptidae.

Parasites on skin - tissue fluid feeders on mammals.

E.g. sheep scab mite Psoroptes ovis can cause ecomonic loss to sheep farming (reduced yields of meat, wool & poor quality skins).

Parasitic arthropods – mites.Parasitic arthropods – mites.

Suborder Sarcoptiformes Family Sarcoptidae.

Parasites in skin - tissue fluid feeders on mammals.

Sarcoptes scabiei, agent of scabies in humans, sarcoptic mange in animals.

Parasitic arthropods – ticks.Parasitic arthropods – ticks.Suborder Ixodida (=Metastigmata) - the ticks.3 families. Family Ixodidae: hard ticks: 675 species -

characterized by presence of anterior dorsal scutum in all stages.

Family Argasidae: soft ticks: 175 species - characterized by leathery, tuberculate cuticle, no scutum (except a mid dorsal sclerite in larva).

Family Nuttalliellidae: - 1 poorly known species from southern Africa - characterized by leathery cuticle and poorly developed anterior scutum. Development unkown.

Parasitic arthropods – Parasitic arthropods – ticks.ticks.Effects of ticks on hosts: Tick paralysis - paralysis of mammal & bird hosts

caused by as yet unidentified toxin. Species of Ixodes and Dermacentor most often implicated.

Ticks are most important vectors of zoonotic diseases of humans.

Important human pathogens/parasites using ticks as vectors include bacteria (rickettsias, spirochetes, etc), protozoa & arboviruses (more about the vectorial / mechanical transmission capacity of ticks in the next lecture).

Parasitic arthropods – Parasitic arthropods – crustaceans.crustaceans.3. Class Crustacea. Parasitism evolved many times within the Crustacea -

only a few instances will be mentioned. Family Lernaeidae.• e.g. Lernea cyprinacea - "anchor worms" - relatively

non-specific ectoparasites of freshwater fish, important pests of hatchery fish. Life cycle with 3 free living, non-feeding nauplius stages; seeks host and goes through 4 copepodid stages as free moving ectoparasite; after mating, adult female imbeds anterior end in tissue and becomes physogastric - can reach 22mm long.

Parasitic arthropods – Parasitic arthropods – crustaceans.crustaceans.Family Ergasilidae. Ergasilus spp. - parasites on gills of both marine

and freshwater fish- 2nd antenna of female modified for attaching to host. Only adult females parasitic, males and immatures free living.

Can be seriously damaging if present in large numbers, especially in hatcheries, e.g. 50% mortality in mullet raised in ponds in Israel.

Parasitic arthropods – Parasitic arthropods – crustaceans.crustaceans.Family Caligidae. Ectoparasites on skin or gills. Adults relatively

unmodified - active on host. Life cycle with free-living, non-feeding nauplius stages, copepodid must find host. Several parasitic copepodid stages (termed "chalimus" forms) preceed adult.

Parasitic arthropods – Parasitic arthropods – crustaceans.crustaceans.Family Lernaeopodidae. Skin parasites of fish. Copepodids "anchor" body

to host by excavating cavity in skin and secreting "cement". Adult with elongate cephalothorax allowing "grazing range".

Parasitic arthropods- crustaceans.Parasitic arthropods- crustaceans.Family Pennellidae. Parasites of marine fish & mammals - among

the largest copepods, some growing to 30cm. Adult females with highly degenerate body - "anchor" processes invade host tissue and enter blood vessels - can be quite pathogenic. Unusual life-cycle involving intermediate host.

Parasitic arthropods – Parasitic arthropods – crustaceans.crustaceans.Class Cirripedia - barnacles & relatives. Order Rhizocephala contains extremely

modified parasites of other Crustacea. e.g. Sacculina.

Class Branchiura. Argulus - "fish lice" - ectoparasitic on fish,

characterized by adults with piercing "proboscis" and modified, sucker-like 1st maxillae.

Summary.Summary.

By the end of this session you should be able to: Appreciate that parasitic arthropods can be

parasites in their own right, or vectors of disease. Describe the main classes of parasitic arthropods. Give named examples from these classes. Appreciate the economic importance and the

implications for public health of parasitic arthropods.

Next session.Next session.

We will:

Explore parasitic arthropods as vectors of disease.