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Parasitic arthropods II

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Pediculus humanus (head & body lice). Phthirus pubis (crab louse). Pediculus humanus. ... humanus capitis (head louse). Parasitic arthropods -lice. Body lice. ... – PowerPoint PPT presentation

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Title: Parasitic arthropods II


1
Parasitic arthropods II
  • Arthropods as vectors of disease.

Dr. Jo Hamilton Parasitology BS
2
Introduction.
  • As we saw in the last lecture arthropods can be
    considered as ectoparasites in their own right
    some arthropods have capacity to become vectors
    of viral, bacterial, protozoal helminth
    diseases.
  • During this lecture we will investigate
    arthropods as vectors of disease.

3
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 some of the main vectors of medical and
    veterinary importance the diseases they
    transmit.
  • Give named examples of arthropod disease vectors.
  • Appreciate the economic importance the
    implications for public health of these arthropod
    vectors.

4
Arthropods.
  • As we saw previously 3 of the 4 arthropod groups
    contain parasitic species.
  • Some of these are important not only as ecto- or
    endo- parasites in their own right but as vectors
    of disease.
  • We will consider vectors of medial veterinary
    importance. During this lecture we will consider
  • Insecta (Lice, Bugs, Fleas Flies)
  • Arachnida (Ticks Mites)
  • Information regarding Crustaceans as disease
    vectors can be found in the lecture notes.

5
Parasitic arthropods - lice.
  • Class Insecta, Order Anoplura, Family Pediculidae
    - the lice.
  • Until recently in human history, lice were such
    common companions of Homo sapiens that they were
    considered one of life's inevitable nuisances for
    rich and poor alike.
  • Host specific.
  • Lice still very common in developing countries.
  • Greyish in colour, dorso-ventrally flattened,
    both sexes feed on blood through mouthparts
    designed for piercing and sucking.
  • They are apterous (wingless).

6
Parasitic arthropods -lice.
  • Two species parasitize humans
  • Pediculus humanus (head body lice).
  • Phthirus pubis (crab louse).
  • Pediculus humanus.
  • Two forms
  • Pediculus humanus humanus (sometimes called
    Pediculus humanus corporis - body louse).
  • Pediculus humanus capitis (head louse).

7
Parasitic arthropods -lice.
  • Body lice.
  • Body lice spend most of the time in their host's
    clothing.
  • Eggs or nits are cemented to fibres in the
    clothes
  • Females lay about 9-10 eggs per day (about 300 in
    her lifetime)
  • Crowding conditions facilitate transmission of
    lice (e.g. poverty, refugee situations, mass
    migration, civil unrest etc).

8
Parasitic arthropods -lice.
  • Head Lice.
  • Smaller that body lice.
  • Nits are cemented to hairs.
  • More prevalent on the back of the neck, behind
    the ears.
  • Not life threatening but causes considerable
    discomfort.
  • Scratching leads to dermatitis or secondary
    infection.
  • Matted hair

9
Parasitic arthropods -lice.
  • Phthirus pubis - Crab louse or crabs.
  • Dwells mainly in the pubic region but it could be
    found in the armpits, beard, moustache, eyebrows
    and eyelashes.
  • Nits are cemented to the hair.
  • Females deposit about 30 eggs during her life.
  • Infection is through contact with bedding or
    other objects, especially in crowded conditions.
  • Transmission is often venereal.

10
Parasitic arthropods -lice.
  • Lice as vectors of disease.
  • Typhus.
  • Caused by Rickettsia prowazekii.
  • Epidemics associated with conditions that favour
    heavy infestations of body lice.
  • Played major role in important wars.
  • Expulsion of the Moors in Spain, Thirty year war,
    World War I (25 million cases, 3 million
    deaths).1971- over 10,000 cases reported, about
    100 deaths.
  • Typhus is fatal for lice.

11
Parasitic arthropods -lice.
  • Trench fever.
  • Caused by another Rickettsia (Rochalimaea
    quintana).
  • Debilitating disease transmitted by Pediculus
    humanus humanus.
  • Epidemics during World War I and II.
  • Long convalescence.

12
Parasitic arthropods -lice.
  • Relapsing fever.
  • Cause by a spirochete, Borrelia recurrentis.
  • 1971- 4700 cases, 29 deaths.
  • Mostly South America, Africa and Asia.
  • Control of lice louse-borne disease
  • Insecticides.
  • Personal Hygiene.
  • Laundering of garments.
  • N.B. In conditions that favour heavy louse
    infestation (war, mass migration, refugee
    situations etc.) hygiene laundry may be
    impossible or low priority.

13
Parasitic arthropods - flies.
  • Class Insecta, Order Diptera the flies.
  • Diptera are the most medically important insects
    causing more than a million deaths each year.

14
Parasitic arthropods - flies.
  • Class Insecta, Order Diptera (flies), Family
    Culicidae (the Mosquitoes).
  • Mosquitoes most widespread important vectors of
    human and animal diseases.
  • There are two blood-feeding subfamilies of
    mosquitoes, Anophelinae and Culicinae.
  • Vectors of protozoa, filarial nematodes,
    arboviruses.
  • Only female feeds on blood. Male requires only
    sugar meal for survival.

15
Parasitic arthropods - flies.
  • Family Culicidae , subfamily Culicinae, Genus
    Culex.
  • Members of this genus are the main vectors of
    West Nile Virus.
  • Culex pipiens (house mosquito) main vector of
    Western equine encephalitis St. Louis
    encephalitis.
  • Culex spp. are vectors of the filarial nematodes
    Dirofilaria immitis Wuchereria bancrofti

16
Parasitic arthropods - flies.
  • Family Culicidae, subfamily Culicinae, Genus
    Aedes.
  • Vector of disease, mainly viruses.
  • Aedes aegypti also known as Yellow fever
    mosquito.
  • Yellow fever is a very serious zoonosis
    responsible for millions of deaths during
    epidemics.
  • Also a vector for Dengue or breakbone fever.
  • 4 strains varying severity. Dengue hemorrhagic
    fever severe form of disease - skin haemorrhages
    significant mortality.

17
Parasitic arthropods - flies.
  • Family Culicidae, subfamily Anophelinae, Genus
    Anopheles - mosquitoes as vectors of protozoal
    parasites.
  • Female Anopheles mosquitoes ingest Plasmodium
    gametocytes from infected human hosts and the
    sexual phase of the parasite occurs within the
    gut, resulting in thousands of sporozoites being
    released into the body cavity.
  • The sporozoites find their way to the arthropod's
    salivary glands where they are transmitted to
    human while the mosquito takes a blood feed.

18
Parasitic arthropods - flies.
  • Within the host red cells Plasmodia reproduce
    asexually eventually burst from the erythrocyte
    invade other uninvolved red cells.
  • This event produces periodic fever anaemia in
    the host, a disease process known as malaria.
  • The four spp. causing malaria in humans are
    Plasmodium vivax, Plasmodium ovale, Plasmodium
    malariae, Plasmodium falciparum.

19
Parasitic arthropods - flies.
  • Family Psychodidae (the sandflies) - Sandflies as
    vectors of protozoal disease leishmanisis.
  • Localized cutaneous lesions or ulcers are
    produced by infection with one of the Leishmania
    sp.
  • L. tropica in the Old World L. mexicana in the
    New World.
  • L. braziliensis is the cause of American
    mucocutaneous leishmaniasis (espundia), L.
    donovani of kala azar, a disseminated visceral
    disease.

20
Parasitic arthropods - flies.
  • All four species transmitted by nocturnally
    feeding phlebotomine sandflies.
  • These sandflies are small, delicate, short-lived
    biting insects, found in animal burrows
    crevices throughout tropics subtropics.
  • The blood meal transfers Leishmania to the flies,
    where the parasites multiply within the gut
    mature.
  • The mature promastigotes are injected into skin
    of new mammalian host where they are taken up and
    multiply within macrophages.

21
Parasitic arthropods - flies.
  • The disease is a zoonotic infection of tropical
    subtropical rodents particularly common in areas
    of China, India, Asia Minor, Africa, around the
    Mediterranean, Central America.
  • In the Mediterranean area, southern Russia,
    India, human disease involves urban transmission,
    with the domestic dog serving as the reservoir.
  • Direct human-to-human transmission also occurs.
  • Sandflies can also be vectors of arboviruses (see
    lecture notes for details).

22
Parasitic arthropods - flies.
  • Family Simuliidae (the blackflies).
  • Certain species of adult blackflies of the genus
    Simulium responsible for transmission of the
    filarial nematode, Onchocerca volvulus, the
    causative agent of river blindness in central
    and western Africa.
  • Certain species can also transmit various forms
    of cattle onchocerciases.

23
Parasitic arthropods - flies.
  • Family Simuliidae (the blackflies).
  • Important vectors species include
  • Simulium damnosum - important vector species in
    Africa.
  • Simulium ochraeum - important vector species in
    New World
  • Simulium venustum - notorious pest species in
    North America.
  • Simulids are also vectors of Leucocytozoon spp.,
    protozoans causing "malaria" in birds. Some
    species cause important diseases of domestic
    poultry, notably turkeys and ducks.

24
Parasitic arthropods - flies.
  • Suborder Brachycera, Family Tabanidae the
    horseflies deerflies.
  • Tabanids are mechanical vectors of important
    bacterial pathogens such as agents of anthrax
    (Bacillus anthracis) tularemia (a disease
    caused by the bacterium Francisella tularensis).
  • Pathogens are carried directly on the mouthparts,
    there is no multiplication of bacteria in the
    fly's body (refer to definition of mechanical and
    biological vectors in lecture notes).

25
Parasitic arthropods - flies.
  • Tabanids are also vectors of Loa loa, a filarial
    nematode.
  • Humans are the only host.
  • Loa loa is distributed throughout tropical
    Africa. Worms live in subcutaneous tissue and the
    migration of worm causes pain and tissue
    swelling.
  • This parasite is often called the "eye worm"
    because worms migrating through the conjunctiva
    of the eye are visible.
  • Vectors are species of Chrysops (deerflies). C.
    dimidiata is the most important.

26
Parasitic arthropods - flies.
  • Family Glossinidae, genus Glossina - the tsetse
    flies.
  • Tsetse's are hosts vectors of trypanosome
    protozoans of the genus Trypanosoma brucei
    species complex which cause serious disease in
    humans and cattle.
  • These are invasive blood tissue parasites that
    produce highly morbid, frequently lethal diseases
    via insect host transmission.
  • The diseases caused by trypanosomes are limited
    to the semitropical tropical niches of the
    tsetse host.

27
Parasitic arthropods - flies.
  • Trypanosoma brucei gambiense causes "sleeping
    sickness" in humans, an often fatal disease
    characterized by lethargy leading to coma.
  • T. brucei rhodesiense is more rapidly pathogenic
    in humans, with death occurring within a few
    weeks before coma ensues.
  • T. brucei brucei causes a fatal disease in cattle
    called nagana.
  • The human forms cause zoonotic diseases wild
    ungulates are the reservoir hosts are not
    affected by the parasites.

28
Parasitic arthropods - flies.
  • Tsetse flies are of as much concern
    agriculturally as they are medically.
  • Infected flies render millions of square
    kilometres of land unusable for cattle-rearing.
  • However, because ranching has been precluded it
    can be argued that the prevalence of tsetse and
    the trypanosomes has protected Africas big
    game animals.

29
Parasitic arthropods -bugs.
  • Class Insecta, Order Hemiptera (bugs). Family
    Reduviidae (kissing or assassin bugs).
  • Vectors of Trypanosoma cruzi (Chagas disease).
  • Bugs of the genera Triatoma Rhodinus are
    responsible for transmission of Chagas Disease
    (South American trypanosomiasis) caused by the
    protozoan Trypanosoma cruzi.
  • Both sexes feed at night on blood using piercing
    and cutting mouthparts. Some species
    particularly like to bite the face lips - nasty
    considering these bugs can be up to 5 cm in
    length!

30
Parasitic arthropods -bugs.
  • Up to a third of a gramme of blood can be
    consumed per feed.
  • Transmission of T. cruzi to the bug is
    accomplished through the mouthparts, but
    transmission to man occurs by scratching the
    faeces (containing the parasite) of the bug into
    the skin.
  • Vectors often defecate while feeding - infective
    protozoans in faeces can enter the wound (bite
    site) when scratched.

31
Parasitic arthropods -bugs.
  • Infected bugs may remain infectious for up to 2
    years.
  • Also possible to contract the disease through
    blood transfusion of poorly monitored blood.
  • Endemic areas include Central South America.
  • The trypomastigotes disseminate from the site of
    inoculation to circulate in the peripheral blood
    of their human hosts.

32
Parasitic arthropods -bugs.
  • Clinically, the infection presents as an acute
    febrile illness in children a chronic heart or
    gastrointestinal illness in adults.
  • Control of reduviid bugs Chagasdisease.
  • Improved construction,
  • Insecticides.
  • Replacement of dirt floors with cement.

33
Parasitic arthropods - ticks.
  • These are epidermal parasites, large in size,
    (macroscopic).
  • Feed on blood.
  • Can be vectors of disease
  • Infestation with ticks can result in
  • Anaemia- Blood loss due to heavy infection can be
    considerable.
  • Dermatitis -Inflammation, swelling, ulcerations
    itching.
  • Paralysis -Tick paralysis common in humans when
    they are bitten near the base of the skull.
  • Otoacariasis- Infestation of the ear canal.

34
Parasitic arthropods - ticks.
  • Ticks can transmit viruses, bacteria protozoa.
  • Family Ixodidae - Hard ticks.
  • Hard ticks are of economic importance in the
    transmission of a variety of diseases.
  • The tick genera Rhipicephalus, Hyalomma
    Amblyomma transmit Theileria parva (similar life
    cycle to malaria also called East Coast Fever)
    a parasite of livestock Boophilus transmits
    Babesia (similar to Theileria) to small mammals
    and dogs.

35
Parasitic arthropods - ticks.
  • Ixodes spp. are the principal vectors of Lyme
    Disease caused by the spirochaete Borrelia
    burgdorferi.
  • Common in the Northeastern USA
  • Leading arthropod transmitted infection in the
    USA.
  • Disease is transmitted to humans by the bite of a
    small tick of the genus Ixodes and is
    characterized by the "bulls-eye" lesions that
    begin at the site of the tick bite.
  • Sequelae may include arthralgia, arthritis
    other immune complex deposition manifestations.
  • Mice and deer constitute the main animal
    reservoir of B. burgdorferi within ticks.

36
Parasitic arthropods - ticks.
  • The rickettsial disease Rickettsia rickettsii
    (Rocky Mountain Spotted Fever) is transmitted by
    Dermacentor.
  • Decamentor andersoni is the main vector of
    Colorado tick fever virus, Rocky Mountain spotted
    fever.

37
Parasitic arthropods - ticks.
  • Family Argasidae - Soft ticks.
  • The tick Ornithodoros is a vector for the
    spirochaete Borrelia duttoni the plague-like
    bacterium Francisella tularensis that causes
    tularemia.
  • Ornithodoros hermsi is the mains vector for
    Borrelia recurrentis (relapsing fever)
  • Ornithodoros has been kept for 19 years alive in
    captivity.

38
Parasitic arthropods - fleas.
  • Order Siphonaptera ( the fleas).
  • One of the most important insect pests.
  • They have piercing/sucking mouthparts that they
    use to find a small blood vessel.
  • Saliva is injected into the area near the
    puncture site.
  • Eggs can remain dormant for up to 200 days.
  • Fleas can survive long periods as adults without
    food.
  • Fleas are not very host specific.

39
Parasitic arthropods - fleas.
  • Fleas can be vectors of human disease including
  • Plague (pest or Black Death).
  • Caused by Yersinia pestis
  • Bacterium releases potent toxins that act on
    mitochondrial membranes, inhibiting ion uptake
    interfering with the normal functioning of the
    respiratory chain.

40
Parasitic arthropods - fleas.
  • Murine (Endemic) Typhus.
  • Flea-borne typhus.
  • Caused by Rickettsia mooseri.
  • Similar to louse-borne typhus.

41
Parasitic arthropods - fleas.
  • Fleas as vectors of helminth diseases.
  • Some fleas are intermediate vectors of the
    cestodes Diplylidum caninum (dog parasite) and
    Hymenolepis diminuta (rodent parasite).
  • Eggs of these helminths are present in the faeces
    of dogs and are ingested by larval fleas.
  • The mammalian host during grooming ingests the
    flea and thus becomes infected.
  • Fleas are the primary intermediate host of a very
    common tapeworm of domestic pets, Dipylidium
    caninum.

42
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 some of the main vectors of medical and
    veterinary importance the diseases they
    transmit.
  • Give named examples of arthropod disease vectors.
  • Appreciate the economic importance the
    implications for public health of these arthropod
    vectors.
  • Please see the lecture notes for additional
    information suggested additional reading.
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