Arthropods/ Ectoparasites Flashcards
What is an ectoparasite?
Parasites that live on the outside of the host, either on or in the skin or the outgrowths of the skin
Give examples of arthropods and the subspecies within that?
Insects
Lice, biting and chewing flies
(Includes flea, jigger flea, simulium, bed bug, bot flies and screwworm- not covered here in detail)
Arachnids
Ticks and some mites
(Includes chigger mites- not covered here in detail)
Annelids
Leeches
Linguatula serrate
What are the main arthropod parasites?
Whats the name of the human and equine Bot fly- warble- Oestridae?
Dermatobia hominis- human bot fly
Gasterophilus intestinalis- equine bot fly
Tell me about the bot fly
Bot fly-
Botflies deposit eggs on a host, or sometimes use an intermediate vector - housefly, mosquitoes, or for Dermatobia hominis, ticks. botfly attaches to the body under the wings.
Larvae from these eggs, stimulated by the warmth of a mammal host, drop onto its skin and burrow underneath
Tell me about the equine botfly/ warble eggs
The equine botflies/ warble eggs laid on the insides of horses’ front legs or nose, depending on the species- the eggs are transferred to the mouth and swallowed-the larvae hatch and attach themselves to the stomach lining or the small intestine or even mouth. The larvae remain attached and develop for 10–12 months before passed.
What do the bot fly have on their surface and why?
Have spines on their surface which work to prevent the removal of the bot fly
Whats the life cycle of the jigger- flea Tunga penetrans?
Endoparasites don’t tend to cause diseases directly, give some examples…
Simulium- black fly
- Onchocerca volvulus
- river blindness
Flea
- Cat flea (Ctenocephalides felis)
- Dog flea (Ctenocephalides canis)
- Human flea (Pulex irritans)- not evolved with us as no primates have a flea
- Northern rat flea (Nosopsyllus fasciatus)
- Oriental rat flea (Xenopsylla cheopis)
Bacteria:
- murine /endemic typhus- Rickettsia typhi
- bubonic plague (rodent passage) Yersinia pestis
Virus: Myxomatosis
Helminth: Hymenolepiasis tapeworm, Dipylidium caninum tapeworm
Protozoa: Trypanosome lewisi (fatal to both rats and mice)
Whats the life cycle fo the Cimex lectularius
blood feeder?
Tell me about the Cochliomyia hominivorax/ Screw worm
screw worm (member of blow fly family) is a parasitic species
larvae eat and infest the flesh (healthy and decaying tissue) of living warm-blooded animals (myiasis-Fly strikes)
Eggs laid about wounds or navel in new-born’s
larvae hatch, burrow deep into tissue, screwworm, small spines on each body segment that resemble a screw’s threads., perpendicular to the skin surface.
In blow fly family but parasite (blow flies feed off necrotic tissue) - new world screw worm – there is an old-world form in Asia/ Africa/ India – and now Australia …. Sterile insect eradication
Damage to hide
Secondary bacterial infections
In what ways can insect and arthropod parasites cause disease and how in each way do they do that?
In part of their own life cycle
- Blood feeding
- Live on and in tissues (direct damage and allergies)
As vector for another infectious agent
- Either as a mechanical vector
- Or a secondary host (? Often, they are the primary host)
*
What are the different types of hosts?
Primary (definitive) host
Secondary (intermediate) host
A reservoir host/ paratenic host
Whats a primary host?
Primary (definitive) Host- here parasite reaches maturity and (may) reproduce sexually (or show genetic material rearrangements between individuals). - required in lifecycle
Whats a secondary host?
Secondary (intermediate) Host- harbours the parasite for a transition period, during which specific development occurs (differentiation). - required in lifecycle
Whats a reservoir host/ paratenic host?
A reservoir host/ paratenic host harbours a pathogen indefinitely with no ill effects serves as a source from which other animals can be infected.
No differentiation here- not required in the lifecycle (but can amplify the pathogen)- MAY show asexual/ non differentiative amplification of non-mature stages of a parasite in which they can accumulate in high numbers – i.e., an amplifying host - So pathogen levels can become high enough to become infectious (transmission is either from the reservoir host or from mechanical vector interacting with this host).
The other type of host is a dead-end host, what is this?
A dead-end host -intermediate host that does not allow transmission to the definitive host, preventing the parasite from completing its development. Common in man where consuming human tissue not seen
Humans for tapeworms as cysts e.g., the Echinococcus (canine) or Taenia soleus (porcine) tapeworm. As infected humans are not usually eaten by final host (dog/ pig).
Whats a vector?
An animal that transmits an infectious agent (there are two ways to do this)
What are the two types of vectors?
Mechanical vector
Biologicla vector
Whats a mechanical vector?
A vehicle (without a stage of development or multiplication).
Mechanical vector. E.g., bacterial and virus transfer. The agent is usually carried on the skin or mouthparts of the vector causing transmission from an infected to a susceptible host.
The survival time of the agent in/ on the vector is usually short, and the transmission must be rapid.
Whats a biological vector?
Can undergo development or multiplication in the vector
Biological vector –such vectors are either an intermediate or definitive or paratenic host (i.e., differentiation may occur- cf paratenic host).
As develops/ amplifies in the vector, time elapses between the acquisition of the agent by the vector and it is becoming infective.
Once infective, the vector may remain so for a considerable period if not the rest of its life. Hence more than a single opportunity for disease transmission. E.g., Ticks and Swine fever virus
Tell me about the Culicidae/ mosquito
What are the different species?
The little fly
Females are blood sucking ectoparasites of most groups of vertebrates (including reptiles, amphibians, and fish) some will take haemolymph
Over 4000 species 5 Genuses (~200 will bite man, 5-6 are considered a human danger)
- Anopheles - malaria
- Culex- West Nile, Japanese encephalitis, or St. Louis encephalitis virus and filariasis
- Aedes -dengue fever, yellow fever, Zika virus, chikungunya virus and lymphatic filariasis
Most are not obligate parasites but for larger egg numbers or second egg laying need a blood meal (hatching of eggs less efficient if the female does not take a blood meal)
Attracted to host by CO2 and 1-octen-3-ol- olfactory stimulant
Deet- ?? Inhibits above or a true repellent
The mosquito life cycle
The different stages
Eggs single or arrays dep on species- most are fresh water (usually stagnant) some use salt/ brackish
Eggs can enter diapause if drying seen
Larvae eat microbe / algae sp spiricles for gas transfer as surface (oil- surface tension change) 4 larval instars (5 stages with pupae being the 5th one)
Pupae are active and swim to surface for gas exchange- pupate hanging off water surface
males ~ 5 days as adult- female 14-28 days – temp dependant
papal are motile and go through differentiation. They can stay n this stage for a long time before male and female formed
females take multiple blood feeds where possible to have good reproduction
Tell me about the proboscis and its structure/ function
the labium (labella front part) ensheaths the mandibles and maxilla it bends away from the mouthparts when the mosquito to bites.
The tip of the labella remains in contact guiding the mandibles and the maxillae
The mandibles are pointed the maxillae have outward teeth- the two are levered against each other with the teeth holding into the tissue
The hypopharynx and the labrum are hollow.
Saliva with anticoagulant is pumped down the hypopharynx, and blood is drawn up the labrum.
Maxilla is BELOW mandible here – based on function rather than position
Mandible- the chewing part
Proboscis
How does an individual respond to a mosquito bite?
What is it driven by?
type IV hypersensitivity reaction
(Occasional anaphylactic type I IgE/ mast cell-basophil driven response)
delayed takes several days to develop, not Ab but cell-mediated response.
Driven by MHC class II (Ag from saliva of insect on them) complex on the surface of APCs (usually macrophages) this with macrophage secreted IL-12, stimulates CD4+ Th1 cells activity and proliferation. These secrete IL-2 and IFγ, inducing the release of Th1 cytokines, causing inflammation
What are the immunomodulatory proteins in mosquito saliva with haemostatic and vasodilatory effects?
- apyrase and 5 nucleotidase, - destroy ADP and ATP – ADP and ATP cause clotting so by destroying them you block platelet mediated clotting by destroying ADP and ATP can lead to 3 and 4
- antithrombin, antifactor Xa- protein – Block humeral clotting
- vasodilatory salivary peroxidase- produced by mosquito and this causes vasodilation
- nitrophorins – indirectly make nitric oxide, transfer system driving vasodilation, (also inhibit platelet aggregation and inflammatory effects of histamine)
- D7 proteins may block host haemostatic and inflammatory molecules
Free adenosine stronger or as strong vasodilator as ADP/ATP and prevents clotting
Thrombin = factor 2
Th-1 cytokines IFN-γ, IL-2, and TNF-α-
Tell me the stages that occur during type I (immediate) hypersensitivity
Whats the pathogenesis of type IV hypersensitivity?
Apyrase- from Schistosome- similar enzyme in mosquitoes and black flies
Tell me about the D7 group of proteins
- suppresses TNF-α release,
- suppression of IL-2 and IFN-γ production
- inhibits T and B cell proliferation
- increases levels of IL-4 andIL-10
antihemostatic, anti-inflammatory, and immunomodulatory compounds
Mosquito salivary proteins (MSPs), drive vasodilation, blocks more rapid classical immune responses but still results in a delayed hypersensitivity
This modulation of the host immune response - can lead to enhance spread of infections- hence a very good system if mosquito used as a vector!
Il4/10 limit inflammation – hence get a slower th1 effect, with activated macrophages … rather than the rapid mast cells response
NB some if these proteins will reduce both Th1 and Th2 responses
As some of these proteins can reduce the Th1 and Th2 response, what does this allow the mosquito to do?
- flying, can migrate long distances
- water dwelling parasite (not needing large bodies of water)
- modifies the immune system of the host
- many mosquitos spp. have often a spectrum of hosts to feed off- zoonotic potential
- diapause stage
- prolific
- feed multiple times
What is the most dangerous animal on the planet?
Culicidae
Name some viral diseases
Aedes aegypti
Yellow fever virus- Parentic host (virus can replicate in the mosquito gut)
Dengue fever- Parentic host (virus can replicate in mosquito and spread between mosquitos)
Chikungunya- ?? – mechanical vector-SEE NEXT SLIDE
Zika virus – unknown
Culex species
West nile virus- Parentic host (virus can replicate in the mosquito and spread between mosquitos)
Culiseta melanura
Equine encephalitis virus
Name a parasitic disease
Anopheles
Plasmodium (eg falciparum) malaria
Many species
Wuchereria bancrofti, Brugia malayi, and Brugia timori. -lymphatic filarisis
name a bacterial disease
Many species (also ticks) Tularemia (Francisella tularensis)
Chikungunya virus
Two changes to the structure of E1 makes the virus more likely to enter mosquito cells and replicate after the insect has fed on the blood of an infected person
Francisella tularensis
Mosq. Vector… biological weapon in respiratory form
What is the parasitic name for lice and what organisms are they found on?
Phthiraptera obligate parasites, small wingless insects (0.5 -5mm long)
Found on almost all species of bird and mammal (not bats)
What are the two forms of lice and what do they do?
Chewing lice feed on skin feathers and debris (bird louse)
Sucking lice pierce the skin and feed on blood (pig louse)
What do lice require throughout their life cycle?
Generally live whole life cycle on the host so need close contact or contact with bedding to transfer
What are the two species of human lice?
Pediculus humanus (capitus/ humanus)- can be interbred, but all offspring behave as capitus- head form… sucking lice… brown colour is blood
Phthirus pubis- also sucking- note thin jaws
What type of response do lice cause?
A type IV response to biting and inflammation- skin irritation
What occurs in long-term lice infestations?
In long-term infestations “vagabond’s disease” skin becomes thickened and deeply pigmented.
When a scientist allowed around 800 lice to feed on him twice a day, what did he say he experienced?
“I almost immediately a general muscular tired feeling in the calf of my legs and along the shins. An irritable and pessimistic state of mind developed. An illness resulted with symptoms very similar to grippe (influenza) and a rash similar to German measles, particularly over the shoulders and abdomen.”
Name two diseases which used body lice as vectors
Epidemic typhus
Louse born relapsing fever
Tell me about Epidemic typhus
Epidemic typhus (Rickettsia prowazeki) (esp during war or displacents)
- Primary cause of Napoleons retreats from Moscow
- ~WWII > 2 million Russian died from this disease.
- Rickettsia multiply in the epithelial cells of the louse intestine and are voided with the faeces and scratched into the bite by the host, (will actually kill the louse)
Tell me about Louse born relapsing fever
Louse Born Relapsing Fever.
- Borrelia recurrentis (can have 70% mortality rate- seen in camps with after famine)
- Again, the bacteria multiply in the gut of the louse
Tell me about mites
Smaller than ticks
All ticks are parasites, but not all mites are parasites
arthropod (Arachnida) as are ticks so not insects–, mites are smaller than ticks and unlike ticks most are not parasites
What are the parasitic forms of mites that live in the skin?
either stratum corneum (Psoroptioc mites- ear, sheep scab)
or stratum granulosum (Sarcoptic mites)- 2% UK population
or hair follicles (Demodex mites)- perhaps up to 100% in elderly
What is it that causes disease from mites?
Diseases are caused by allergic response to saliva and excreta of the mite
Gives examples of two mite diseases
Psoroptes ovis - sheep scab
Sarcoptes scabiei- one cause of scabies
Tell me about Psoroptes ovis - sheep scab
?? All maybe P equi
Feed off upper layers don’t piece the skin but can lead to severe immunoreactions
Tell me about Sarcoptes scabiei
(One causes of scabies)
The track of the mites within the skin produces an intense irritation about the burrow, a delayed cell-mediated inflammatory response to allergens
Tell me about human scabies
disease in >300 million people (in some populations ~ 80% carry the mite)
most common in women at about 20 years of age, cannot get rid of without treatment
Scabies infection with the female Sarcoptes scabiei mite
Often only ~ ten mites involved in an infection
Classical type IV delayed cell immune response
Scabies spread through physical contact or sharing of clothes, towels, and bedding,
Mites survive only two to three days from host at room temperature.
Give some other examples of mites causing scabies?
Sarcoptic mange
Sarcoptes scabiei canid
Cheyletiella
What are ticks?
Blood sucking vertebrate ectoparasites (ie reptile ticks exist)
Arthropods like mites but all are parasites- unlike mites
What are the three forms of ticks?
Nuttalliellidae- (single species with wide spectrum of hosts- Mammals. Birds and Reptiles)
Hard ticks –Ixodidae (have a shield on back)
Soft ticks – Argasidae (no shield)
What are the british tick fauna?
22 British species recorded
19 Hard ticks (Ixodid)
- Dermacentor reticulatus
- Haemaphysalis punctata
- Hyalomma marginatum – (imported by migrant birds)
- Rhipicephalus sanguineus (imported by pets, not native)
15 Ixodes species
- 7 principally bird ticks
- 6 principally mammal ticks
- 2 mammal and human ticks
3 Soft ticks (Argasid)
- Argas/Carios
- Ornithodoros – rarely imported on seabirds
Dermacentor reticulatus – ORNATE TICK11
Haemaphysalis punctata
- red sheep tick,
What type of ticks can you get?
One, two and three host ticks
NB. all have three post hatch stages; larvae, nymph and adult
Give an example of a one host tick and its life cycle
Give an example of a two host tick and its life cycle
Give examples of three host ticks and their life cycle
Ixodes parasites of humans
- Ixodes heagonus
- Ixodes ricinus
Tell me about the larva, male and nymph/ female of the ixodus ricinus
Larva – 3 pairs of legs
Male – scutum covers entire body
Nymph and Female are similar
female much larger with genital aperture and porose area
Why are Ixodes ticks unique?
ixodes ticks are unique in long duration of attachment to the host, - from several days up to weeks depending on life stage and tick species.
When feeding, female ticks can increase their weight more than 100-fold in one blood-meal uptake…. Salivary components are – vasodilatory, increase angiogenesis, stop clotting, modified the innate and acquired immune responses
Summary
- Typically, Multiple hosts
- Very wide host range (temperature and moisture of environment more defining species)
- Each stage attaches to host and remains attached till engorged –(days or weeks)
- Can produce a blood sinus about mouthparts to help feeding
- Ixodes ricinus- a three-host life cycle,
- generally, 3 years to complete, 1 to 6 years (dependant on climate).
- Adults feed on mammals/ birds (6-12 days) before mating on host and dropping off
- The resulting nymphs seek their host, small-medium sized mammals, or birds (2-6 days)
- The larvae feed off rodents, hedgehogs’ rabbits, birds, reptiles for 3–8 days before dropping off and moulting (not active in searching for host)
- Despite the name (deer tick) their main host are birds
In what three ways can ticks cause diseases directly?
1. Only if very severe blood loss
Despite the name (deer tick) their main host are birds
2. Hypersensitivity
Usually classical type IV (rare anaphylaxis)
3. Toxins (present in saliva)
Tick paralysis (neurotoxin- never described in UK but it has in Australia)
certain species Ixodes including
Ixodes ricinus
Ixodes holocyclus
Holocyclotoxin-1: from Australian may block acetyl choline release at NMJ which leads to paralysis
Why are ticks good vectors?
- Feed for long periods
- Have up to three separate hosts
- Modulate the immune system
- Cause increased blood flow and angiogenesis
Can be excellent vector for other agents… bacteria, protists, viruses…
Name some bacterial diseases that ticks cause as vectors?
Lyme disease (Borrelia burgdorferi)
Relapsing fever (different Borrelia species and various ticks)
Typhus- (Spotted Fever)- Rickettsia bacteria
Rickettsia rickettsii
Rickettsia Helvetica
Cattle tick-borne fever (Anaplasma phagocytophila
Ehrlichiosis anaplasmosis (Ehrlichia chaffeensis)
Tularemia (Francisella tularensis)
Sheep tick pyemia (Staphylococcus aureus),
Typhus -Rocky Mountain Spotted Fever/ Helvetica Spotted fever- – fever and headache, rash -septicaemia muscle pains and vomiting.
Ehrlichiosis- headache, muscle aches and fatigue –immunospression , CNS signs coma - death
Tell me protozoa infections that ticks can cause
Babesiosis (Babesia microti, B. equi)- cattle versions cause red water fever
Babesiosis (Babesia microti, B. equi) protozoal parasite mammals and birds
Babesia lives intracellularly within RBC and undergoes binary fission?
Name some viral infections that ticks can cause by being a vector?
Tick-borne meningoencephalitis
Colorado tick fever
Crimean-Congo haemorrhagic fever
Severe Febrile Illness
ASFV (African swine fever virus)
Ticks can also cause a viral induced allergy, tell me what this allergy is and what causes it?
An induced allergy
Meat allergy (can be allergic to meat)-
IgE reaction to galactose-alpha-1,3-galactose. Tick bites transfer this carbohydrate causing delayed allergic response.
Then allergy to consumption of mammalian meat products.
Galactose-alpha-1,3-galactose a sugar not produced in apes, (but is in other mammals on muscle)
What are some reasons why xenotransplants won’t work for ticks
Tick-borne meningoencephalitis – Flavivirus, infects many mammals including man
ASFV
Colorado tick fever- fever, later encephalitis/ meningitis
Meat allergy - a delayed onset, 3–8 hours after the consumption of mammalian meat, severe itching, hives, gastrointestinal upset, possible anaphylaxis /respiratory distress
