Biology of ectoparasites: Nuisance and their role in disease transmission Flashcards
Phylogenetic tree of insects?
Parasites are from Animalia kingdom
Antropoda phylum has Insecta and Arachnida (spiders,ticks) classes
Insecta has: order of Coloptera: beetles, order of lepidoptera: butterflies
All 4 winged
except order of the diphtera: 2 winged insects
Role of antropodes in human health?
They can cause:
- ectoparasitosis (causes disease from outside the body): eg. mite
- endoparasitosis (causes disease from inside the body): eg. fly larvae that causes myasis (invasion of tissues)
- poisoning: eg. wasp,bee,spider sting
- allergy: eg. housedust mite: often skin, feces, excretions of mite causes allergy
- nuisance (disturbance) eg. midges and black flies in summer, can’t even sit in some places in Scotland, hundreds of midges try to suck your blood xD
- delusionary parasitosis: people get delusional and think they have insects everywhere: call spraying companies etc. when theres nothing = psychological
- antropods as vectors of disease agents (virus,bacteria,parasite)
eg. malaria, ticks, tsets flies, bugs, fleas etc.
Do vector borne diseases decrease or increase recently? /examples
They increase in past decade
eg. Lyme in USA
West Nile Virus, wasn’t even found in USA before, it popped up now
West Nile Virus also reported in NL: found on a bird first during monitoring, then found in pools of mosquitos, 2020: first case reported, at that year there was exceptional heat wave in summer, might be the reason, 2021: no case
Dengue increased
Plague outbreak:
Plague is often associated w the Middle ages in the Western world, but in October 2017 it caused an outbreak: killed tens of cases each day
Pneumonic plague increased: its the most common and dangerous one - also can be transmitted from human to human after the flea bite
Why vector borne diseases increase?
Climate change increases temperature = the living area of insects increase
Ectoparasites definition
Organisms living at the expense of other hosts on external surfaces
They can also cause damage as the result of blood feeding, crawling, scraping skin
Ectoparasites examples/not vectors
1) Bloodsucking louse:
Obligate human ectoparasite: Common in primary schools, sometimes it is advised to parents to check their kids
It has a flattened body, 6 legs w claws = can attach hair easily and grasp
It feeds from head a couple of times a day, causes itching
It lays its eggs on hair, at some point new louse crawls out
-Selfies increased the headlouse in secondary school xD Direct hair to hair contact allows louse to crawl to next person without falling down: once it falls down it dies fast usually
2) Bloodsucking crab louse (Phiturus pubis)
Way less common, its an STD (can be transmitted human to human w sex) and it grows on pubic hair xD - Its almost an endangered specie
Its really accustomed to living in genitalia environment, its structure makes it only survivable in pubes, cant live on curly hair xDD
*Head louse: lives on head
*Body louse (also exists) lives on body
*Crab louse: lives on pubes
All have different niche, and can’t live on others places
3) Blood feeding bed bugs: bite really bad
They come out at night, live in the cracks of houses or under beds in morning w/ other bugs = has a flattened body that can hide easily
Wingless, doesn’t spread disease but bites very hard
Resistant to insecticides, you treat them by increasing whole temperature to 60 degrees in room= this might hurt the furniture, also 200 euro per room, really expensive & a problem in often hotels
4) Harvest mites: cause allergy
They have an orange color, they live on grass
if you walk with bare feet or legs, the mite can hop on you and feed on ur tissue by secreting something that melts your tissue off, causing huge irritation
5) Poultry red mite: Causes nuisance in poultry
Often found on chicken, %80 of Dutch farms are infected: huge problem on industry
They grow crazy, up to 50.000 of them sucking 1 chicken, very harmful: causes reduced eggs, stress, and death in chickens
Also makes poultry farmers itchy
Doesn’t transmit any disease
Often forbidden insecticides are used to control them
6) Myiasis: invasion of animal tissues by antropods, Dermatobia hominis
1) This Dermatobia fly lays its eggs on another insect like mosquito
2) Mosquito carries its eggs to animal (phoresis: hitchhiking of dermatobia eggs by another insect) and drops them while biting the animal
3) Eggs hatch and eat the whole tissue, eggs develop to larvae as they feed
4) Larvae drops to floor, pupates and becomes fly
This causes economic damage, many holes on the skin of cattles for eg.
Also this can happen in humans, ew huge larvae went inside the eye ew, it just feeds on tissue the same way
Vectorborne diseases caused by:
A lot of mosquitos, tsetse fly, kissing bug (Chagas), ticks, snails, fleas, etc. many species
Ectoparasites as vectors examples / Malaria
Malaria: Is it a past, current, or a future/increasing problem?
Kinda all of them, was common in past, still common today in tropics, and increasing due to global warming
NL: a past disease, back then seen in coastal areas, eggs were in salty water
Plasmodium vivax
MDA w quinine was done, also DDT was used (now banned)
in 1970: NL was malaria-free by WHO, last case seen in the 1950s
Recently: seen in travelers from Africa
Future: other Anopheles are increasing which might also transmit the disease, which might be a problem
Kenya: a current problem
-Plasmodium falciparum (the really deadly one)
-%75 ppl are at risk - %20 mortality of children under 5 years old
(Plasmodium immunity accumulates, not yet developed in kids)
-Control is done by: spraying, nets indoors
now due to this mosquitos might try to bite you outside nets in the morning = selective pressure = the ones that bite very late at night are dead, early biters are selected
Malaysia: a current problem
- plasmodium knowlesi recently found to be causing disease in humans
- %68 of all hospitalization in Malaysia now
- Transmission as far as they know only occurs from macaques as reservoirs (also human to human) they apparently destroyed macaques natural environment w large scale deforestation, they started to look for alternative resources and get closer to humans, which transmits the disease
- also seen now in Indonesia and Thailands
Every malaria species has its own area/depending on where the vector prefers to live, that type of malaria gets common.
eg. Anopheles gambiae, lives in small water puddles
A. darlingi: larger deeper water
A. dirus: small puddles in East
Is mosquitos flying syringes? What happens once we get bitten?
Not really, they have a more intricate feeding system
Mouth has different multiple needles/jaw is like a piercing organ
Mosquito mouth has two different channels: 1st: feeding on blood
2nd: excreting saliva (differs on composition on each mosquito), has coagulants & vasodilators to prevent blood clotting/widen blood vessel for easier feeding
To saliva: Immune system upregulates IgG/IgE antimosquito Ab + histamine,serotonin, bradykinin = itching
Where does these diseases really come from? /how to tackle this?
Wildlife (bat,rodent, primates) = origin of pathogens usually
Domestic (birds,cows, pigs, camels) = sometimes origin, (eg. camel=mers virus)
often a reservoir as livestock
Diseases spillover from both to humans
often vectors bring it from wildlife, to directly us or domesticated animals, once domesticated animals’ infection increase, it spillovers to us
You need to do forecasting/early detection to prevent spillover from wild/domestic animals: Check which diseases can be the next ones that will break out in humans?
eg. Zika virus, once it came out, no one knew where was it from, or the role of mosquito, modelling the disease often gets complicated as more hosts are added, but its necessary
Give rapid response once its already observed on humans, and try to tackle it also in reservoirs
How to calculate the new disease spread?
Basic reproductive number: new infections resulting from the introduction of a new pathogen into an immunologically naive population
If R is bigger than 1, disease spreads, smaller, disease dies out - interventions are done to often redocue the diseases under one, then htey die on their own anyway
This number depends on:
- vector density relative to host (More mosquito= more transmission)
- transmission coefficient, higher coefficient: more transmission
- biting habit
- vector survival rate
- host recovery rate
How to determine whether a vector transmits a disease for real?
Vector incrimination (Barnett, 1962)
1) If there’s common feeding on vertebrate hosts
2) Biological asssociation in time and space of vector and clinical infections
3) Demonstration that field collected specimens has the pathogen (eg. prove malaria is indeed found in your population)
4) Demonstrate efficient transmission under experimental conditions
(expose vector in lab to blood meal coupled w parasite: demonstrate that parasite eventually goes to salivary gland - if it just stays inside its stomach it wont be transmitted)
What barriers pathogen need to pass in order to infect vector successfully?
1) Physical barriers: peritrophic membrane (pass epithelia), go midgut, pass from hemolymph (blood), go salivary gland
2) Vector immune system: Vector can also attack the parasite, microencapsulation, RNAi, antibacterial peptides, innate immunity etc.
Malaria lifecycle/only vector one
1) Blood meal taken from infected host
2) Gametocytes/micro& macrogametes (female/male) fuses and forms ookinete
3) Then it passes from midgut to stomach wall= forms oocysts
4) Oocysts multiply, forms sporozoites, oocytes burst and release sporozoites
5) sporozoites go salivary gland to enter another host
Why malaria elimination progress stalled?
Colombia 2/4 resistance
CoteDivoire 4/4 resistance
India 3/4
Global insecticide resistance is observed= either developing new chemicals or new approaches are needed to control the vectors
Since 2005: insecticide covered bednets are used, since 2010s, vectors started getting resistance, now they can stay on top of nets and look for gaps freely
