Introduction and classification and cost of parasites Flashcards
What is the definition of parasitism?
A non-mutual relationship between species, where the parasite benefits at the expense of the host
What are some general “rules” of parasitology (which may be broken?)
- Parasitism - a non-mutual relationship between species, where the parasite, benefits at the expense of the host.
- Both parasites and hosts have evolved with each other and adapted to each other
- Parasites don’t aim to kill their host
- Parasites can be facultative or obligate
Give an example of an animal which showed parasitism when forced to by circumstance?
Tell me about this parasite and the symptoms it can cause in humans?
The Rat-tailed maggot
- these are the larvae of certain specied of hoverflies
- They live in stagnancy, oxygen-deprived water, with a high organic content
- there have been documented cases of human intestinal myiasis caused by these aggors
- the symmtoms of this are: can be asymptomatic or abdominal pain, nausea, vomiting and pruritus ani
- infection can be caused by ingestion of contaminated food or water
Give some examples of parasites which can live on other parasites
- Nosema podocotyloidis n. sp. (Microsporidia), a hyperparasite
- Parapristipoma octolineatum- a host
- Podocotyloides magnatestis- (Trematode) a parasite
The life cycle of Dipylidium caninum
What are the ways in which diseases can be caused by parasites?
provide an example
- Parasites do direct damage (Dermatobia hominis- human bott fly
Physical and Chemical damage)
- Damage through hyper-immune responses
Culicidae
Aedes aegypti
- Most diseases is because the parasite acts as a vector for other pathogens (Encephalitis viruses)
Some parasitic insects spread diseases. The mosquito is an example of a parasite which spreads viruses
Give an example of a disease which can occur due to the viruses in which mosquitos carry
Some parasitic insects spread diseases
Mosquites VIRUSES
Arboviruses - ARthropod-BOrne virus
Encephalitis viruses is caused by arbovirus which is a disease caused by an arthropod e.g., mosquito
Give some examples of mosquito-transmitted viral diseases causing encephalitis
- Eastern equine encephalitis
- Japanese encephalitis
- La Crosse encephalitis
- St. Louis encephalitis
- West Nile virus
- Western equine encephalitis
- Dengue Fever
- Rift Valley Fever
- Yellow Fever
Give some other examples of mosquito-borne diseases
- Chikungunya virus
- Zika virus
Give examples of other mosquito pathogens
Plasmodium falciparum and others – Malaria
Wuchereria ssp- elephantiasis
Is most parasitic damage direct or indirect?
Give an example
Much (most) parasitic damage is indirect- biting midge- (Culicoides)
WHO- priotory infectious diseases 45% parasitic diseases or related to parasites
Diseases by protozoa and helminths
Tell me where the economic cost of parasitic diseases arises
Nearly half of the world’s population is at risk of malaria.
In 2015,
- ~212 million malaria cases
- ~429 000 malaria deaths (80% under 5 years of age)
Economic costs- Malarial costs – 1% of GDP of all countries were endemic
Direct - (illness, treatment, premature death) at least US$ 14 billion per year.
Indirect -The cost in lost economic growth is ~5 times more than that (estimated at 5% GDP).
700 million people are infected with known mosquito transmitted disease
Context
- 36.7 million people globally were living with HIV (end 2015)
- 2.1 million people became newly infected with HIV (end 2015)
- 1.1 million people died from AIDS-related illnesses (end 2015)
Direct costs (illness, treatment, premature death) at least US$ 19 billion per year
Where does the word parasite come from?
First used in English in 1539, the word parasite comes from the Medieval French parasite, from the Latin parasitus, the latinisation of the Greek παράσιτος (parasitos), “one who eats at the table of another” and that from παρά (para), “beside, by” + σῖτος (sitos), “wheat”, hence “food”. (Wikipedia).
What is a parasite?
There may be more than one definition
- An animal or plant that lives in or on another animal or plant and gets food or protection from it.
- A parasite is a small animal or plant that lives on or inside a larger animal or plant and gets its food from it.
- An animal or plant that lives in or on another (the host) from which it obtains nourishment. The host does not benefit from the association and is often harmed by it.
- An organism that lives on or in a host organism and gets its food from or at the expense of its host.
- An animal or plant that lives on or in another animal or plant of a different type and feeds from it.
What is parasitology?
- The branch of biology or medicine concerned with the study of parasitic organisms.
- A branch of biology dealing with parasites and parasitism especially among animals.
- The branch of biology dealing with parasites and the effects of parasitism.
- A scientific study of parasites, their hosts, and the relationship between the parasite and the host.
- The branch of microbiology that is concerned with the study of parasites. In the process, it gives focus to various characteristics of the parasite (morphology, life cycle, ecology, taxonomy, etc), the type of host they infect/affect and the relationship between the two.
- The study of the interaction between parasites and their hosts. In general, parasitologists tend to concentrate on eukaryotic parasites, such as lice, mites, protozoa, and worms, with prokaryotic parasites and other infectious agents the focus of fields such as bacteriology, microbiology and virology.
- The study of parasites, their hosts, and the relationship between them. As a biological discipline, the scope of parasitology is not determined by the organism or environment in question but by their way of life.
Why should we study parasites?
- They have fascinating, complex and often bizarre life cycles
- They are everywhere
- They have huge medical, sociological, and economic impacts
- They are the reason sex evolved
- They have amazing morphological, immunological, biochemical, molecular, and behavioural adaptations (and may change the behaviour of their hosts).
- We have a morbid fascination with the macabre.
What was the earliest known parasite?
How were they arranged and what effect did they have on their host?
Tube casts on shells of brachiopods from early Cambrian 512 MYA
Orientate with siphonophores, whether single or multiple tubes
Estimated biomass of shells with tubes sig lower than shells without
Estimated biomass of shells increases with distance of tubes from shell opening
Examples of earliest known human parasites? Archaeology
Coprolites:
~6100-7100 BC – Whipworm Eggs - Turkey
~5900 BC - lung fluke eggs – Chile
~5000 BC hookworm eggs – Brazil
~2330 BC – roundworm eggs – Peru
Mummified:
~3000 BC – tapeworm eggs - Chile
~2300 BC – tapeworm eggs – NW Iran
~2000 BC - tapeworm eggs – Egypt
Ancient Egypt – calcified Dracunculus worm – “Mummy 1770”
~1100 BC – filarial worm – Natsef-Amun mummy
~2000 BC – Trypanosoma DNA - Chile
~ 400 BC – Tollund Man – Trichuris, Taenia, Ascaris eggs and proteins
Pelvic Soil:
~8300-7300 BC – roundworm, whipworm, Taenia, Fasciola – Cyprus
~7000-5700 BC – roundworm, whipworm, tapeworm? China
~4000-5800 BC – schistosome eggs – N. Syria
What was the earliest known parasite awareness? History
Egyptian medical papyri
Ebers Papyrus (c1550 BC) guinea Worm - “Wrap the emerging end of the worm around a stick and slowly pull it out.“ (this is where the WHO logo originated from)
Kahun papyrus c1800 BC (and numerous others) – the ‘ā – a – ā disease’ – haematuria - schistosomiasis
China – 3000–300 BC - roundworms, tapeworms, blood flukes, intestinal flukes, hookworms, and head lice
India – 2500-200 BC
Greece – 800-300 BC
Rome - 700-400 BC – Cethegus (160 BC – attempt to drain the Pontine Marshes)
What was the earliest reference to parasites?
Mentuhotep II c2051–2000 BC
Elephantiasis?
Whats symbiosis?
Any relationship between 2 dissimilar organisms
Includes parasitic, commensalistic, and mutualistic relationships between different species (both harmful and beneficial)
Whats mutualism?
Give an example of an organism that shows this
Where two organisms of different species exist in a relationship in which each individual benefits from the activity of the other
Obligate (essential) vs facultative (optional)
Often referred to as symbiosis in the UK!
e.g., lichen which is an association between a fungus and an alga where both benefit from the association - is obligate for the fungus, not necessarily for the alga
Whats commensalism?
In what different ways is this done?
A relationship between two organisms of different species, where one organism benefits from the other without affecting it.
com- (with) and mensa (table)
- food
- shelter (inquilinism)
- transport (phoresy)
- use something created (metabiosis)
Whats a saprophyte/ saprotroph?
An organism that derives benefit (nutrition) from dead or decaying organic matter
Dead or decaying plant matter (saprophyte)
Dead or decaying carrion (saprotroph)
Whats meant by parasitism?
A non-mutual symbiotic relationship between species, where one species, the parasite, benefits at the expense of the other, the host.
Unlike predators, parasites typically do not kill their host, are generally much smaller than their host and will often live in or on their host for an extended period.
The term is generally reserved for eukaryotic organisms, so viruses and bacteria are not normally included
Whats an ecto- parasite and provide examples
Parasites that lives “on” a host
E.g., bed bugs, pubic (crab); cat flea
Whats an endo-parasite and provide examples
Parasites that live “inside” a host
either intracellular or intercellular
E.g., malaria, schistosomes, roundworms
How endo is endo? Hyperparasitism (the parasitic habit of one species upon another parasitic species)
Whats an obligate parasite?
Give an example
Parasite that has to have a host / hosts to complete its life cycle. E.g., Ascaris lumbricoides
Whats a facultative parasite?
Give an example
Parasite that can survive without a host but will probably be more successful if it finds one. E.g., Naegleria fowleri
Naegleria - small single celled amoeba found in warm fresh water (lakes, rivers, streams) – “brain eating amoeba”
Whats a Parasitoid?
A non-mutual symbiotic relationship between species, where one species, the parasite, benefits at the expense of the other, the host
An organism that spends a significant portion of its life history attached to or within a single host organism but unlike a true parasite, it ultimately sterilises or kills, and sometimes consumes, the host
Mostly occurs in insects. Less common in nematodes and mites
Define zoonosis and give an example
- An infectious disease of animals (usually vertebrates) that can be transmitted to humans
- An infectious disease whose normal host range includes both humans and other mammals
- Zoonosis correct definition: an infectious disease whose normal host range includes both humans and other mammals
Schistosoma japonicum: Humans, water buffalo, cattle, rodents, dogs, sheep, pigs, dogs
Whats meant by a direct parasite life cycle (monoxenous)?
Only a single host e.g., pinworms (the most common disease in the world?)
Whats means by an indirect parasite life cycle (heteroxenous)?
Two or more hosts. Sexual reproduction occurs in the definitive (primary) host while larval development occurs in the intermediate (secondary) host(s)
e.g., lancet fluke - Dicrocoelium dendriticum (primary host - ruminants; secondary hosts – snail & ant
Parasite zoonotic diseases endemic in the UK
Parasite zoonotic diseases exotic to the UK
Mitochondrian- parasite or not a parasite?
- Organelle providing energy for eukaryotic (not prokaryotic) cells
- Has an inner and an outer membrane and its own genome
Answer: Endosymbiont (mutualist)
Mistletoe- parasite or not a parasite?
- Plant that lives on deciduous trees (e.g., apple)
- Derive most of their nutrients and water from the host tree
- Do photosynthesize to a small extent
- Cannot live without a host
Answer: Parasite (hemi-parasite because it can generate some of its own nutrients)
Mosquito- parasite or not a parasite?
- Insects of the family Culicidae
- Females of many of the species must have a blood meal before they can produce eggs
- Loss of blood seldom of importance to the victim
Answer: Parasite (and vector)
Malaria- parasite or not a parasite?
- Protozoan transmitted by female mosquitoes when they have a blood meal
- Causes fever, fatigue and in severe cases coma and death
- Cannot live outside a host
Answer: parasite (hyperparasite)
Honey fungus- parasite or not a parasite?
- Attack and kill the roots of many woody and perennial plants
- Lives off living and dead wood
- Mycelium spreads below ground from tree to tree
Answer: Parasite (facultative parasite)
Frigate bird- parasite or not a parasite?
- Steals prey from other animals
- Saves time and effort and is therefore more successful by stealing rather than foraging for itself
Answer: Parasite (kleptoparasite - parasitism by theft). A form of feeding in which one animal takes prey or other food from another that has caught, collected, or otherwise prepared the food.
Tillandsia- parasite or not a parasite?
- Plants grow without soil attached to other plants
- Moisture & nutrients are gathered from the air
Answer: Epiphyte
A plant that grows harmlessly upon another plant. It derives moisture, nutrients from the air and rain and the debris around it.
Remora- parasite or not a parasite?
- Has a sucker to attach it to the surface of a larger marine organism
- Feeds on scraps of food dropped by the host
- Benefits from transport and protection
- May clean off hosts external parasites
Answer: Epibiont (an organism that lives on the surface of another living organism and is harmless to the host), commensal and mutualist
Cuckoo- parasite or not a parasite?
- Adult female lays its eggs in other birds’ nests
- The young hatch and eject the host birds eggs from the nest
- The host birds incubate and rear the young cuckoo
- Each female cuckoo specializes in a host bird (e.g., Dunnock, robin, meadow pipit)
Answer: Parasite (brood parasite)
Yellow rattle- parasite or not a parasite?
- Grows in grassland and derives some of its nutrients from neighboring plants
- Can survive independently
- [helps biodiversity in meadows by suppressing growth of grasses)
Answer: Parasite (facultative or hemi-parasite because it can survive without a host)
Wasp- parasite or not a parasite?
- Adult wasp lays her eggs on the outside of the host caterpillar
- The eggs hatch and feed off the caterpillar until they pupate
- The host dies
- Larvae require host to survive
Answer: Parasitoid (parasite – hyperparasitism)
Bot fly- parasite or not a parasite?
- Family of insects (Oestridae) whose larvae live in a mammal host (either in the skin or the intestines)
- Larvae require a host to develop but rarely cause in infection in the skin
- They drop out to pupate in the soil
Answer: Parasite (facultative/ obligate/ saprophagous)
Give examples of parasites of economic importance?
- Microsporidia- Noseme bombycis
- Mites- Varroa destructor
- Sea lice- Lepeophtheirus salmonis
- Hydatid disease- Echinococcus granulosus
Tell me about Microsporidia- Noseme bombycis
- Group of spore-forming unicellular parasites
- Causes pébrine in silk moths (Bombyx mori) (discovered by Louis Pasteur)
- Largely responsible for the collapse of the silk industry in France, Italy and Germany the late 1800s.
- Once thought to be protozoa, now considered as fungi or sister group to fungi
- Some are hyperparasites of parasitic flatworms
- Some are emerging human parasites of increasing importance
Tell me about Mites- Varroa destructor
- Parasite of honeybees (Apis mellifera & Apis cerana) contributing colony collapse in Europe and N America
- Weakens the bee by sucking the haemolymph and transmits viruses (e.g., deformed wing virus)
- Control methods have limited effect
- Impacts on honey production and pollination
- Est. impact in Australia if gets into Country: US$ 17-39 million per year
- “The total economic value of pollination worldwide amounted to €153
- billion”
Tell me about Sea lice- Lepeophtheirus salmonis
- Copepod ectoparasite parasite of salmon
- Particularly prevalent in farmed Atlantic salmon causing abrasion lesions, loss of blood and stress
- Annual cost to Scottish salmon industry: £26m. 2011 – US$436 in Norway)
- High cross infection with wild salmon and sea trout
- Control methods include use of organophosphates and more recently native wrasse and lumpsuckers as cleaner fish (mutualism)
- Salmon is UKs largest food export – 2019 25% loss due mainly to lice
- 9% of production costs are for lice control
Tell me about Hydatid disease- Echinococcus granulosus
- Tapeworm that is found on all continents and in at least 100 countries
- Eggs are passed from definitive host (dog) in the faeces and picked up by secondary host (e.g., sheep, goats) or by humans as a zoonosis
- More than 1 million people are affected at any one time (WHO figure)
- Economic costs are very high due to poor animal health, meat being condemned and human transmission
- US$ 73 million in Morocco alone (2020)
- 2014 prevalence at slaughterhouses was 12.4% in cattle, 8.7% in camels, 8.4% in sheep and 4.7% in goats
- 2016 Ethiopia – 52% slaughtered cattle
- US$3 billion for treatment and livestock losses per year
Whats the economic impact of DALYs?
One disability-adjusted life year (DALY) can be thought of as one lost year of “healthy” life. The sum of these DALYs across the population, or the burden of disease, can be thought of as a measurement of the gap between current health status and an ideal health situation where the entire population lives to an advanced age free of disease and disability.
Echinococcus granulosus - 871,000 disability adjusted life years (DALY) globally per year.
US$ 73 million in Morocco alone (2020)
2014 prevalence at slaughterhouses was 12.4% in cattle, 8.7% in camels, 8.4% in sheep and 4.7% in goats
2016 Ethiopia – 52% slaughtered cattle
871,000 disability adjusted life years (DALY) globally per year.
US$3 billion for treatment and livestock losses per year
Give an example of a biological control and what it does
Biological control- Phasmarhabditis hermaphrodita
- Nematode (Nemaslug) used to control slugs and snails.
- the grey field slug, Deroceras reticulatum, is the most widespread pest species in the world and is responsible for most agricultural and horticultural losses. Is highly susceptable
- Bought as eggs and watered into ground near susceptible plants
- lettuce, strawberries, and glasshouse orchids and low value field crops such as Brussels sprouts, wheat, potatoes, and oilseed rape.
- Also, parasitic wasps for caterpillar control (parasitoid)
- parasitic fungi for control of other parasitic fungi (hyperparasitism)
- Nemasys - Steinernema feltiae for leatherjackets
Tell me about neglected tropical diseases (NTDs)
Give an example
One in seven of the worlds population suffers from one or more neglected tropical diseases – many are parasites
https://www.youtube.com/watch?v=DfP-dv_P7rk
These diseases such as dengue, lymphatic filariasis, trachoma and leishmaniases are “neglected” because they generally afflict the worlds poor and historically have not recieved as much attention as other diseases
example: lymphatic filariasis
Tell me about malaria and what parasite it is due to
Malaria- Plasmodium spp.
- Protozoan parasite transmitted by mosquitoes
- fever, fatigue, headache, coma death
- Infects (mainly) liver & red blood cells
- 2020 241 million cases and 627,000 deaths (219 million cases, 435,000 deaths in 2017)
- 3.2 billion at risk & 1.2 billion at high risk
- Malaria was endemic in England until beginning of 20th century (“Marsh fever” the “ague” or “intermittent fever”)
- Sub Saharan Africa carries a disproportionately high share of the global malaria burden. In 2020, the region was home to 95% of malaria cases and 96% of deaths. Children under 5 accounted for 80% of al malaria deaths in the region.
- ? Used as biological warfare in Italy at end of WW2?
Tell me about sleeping sickness and what parasite it is due to
Sleeping sickness- Trypanosoma spp.
- Protozoan parasite transmitted by tsetse flies (African)
- Hosts: both humans & cattle
- Infects blood and spinal fluid
- Symptoms: Headache, fever, joint pain, neurological
- 20,000 (estimated) cases in 2012. 65 million at risk (WHO figures)
- Countries endemic for human African trypanosomiasis (HAT), also known as sleeping sickness, continue to report fewer cases, indicating that the disease is well on course for elimination as a public health problem by the end of this year.
- In 2000, there were 26 550 confirmed cases reported to WHO. Sustained control efforts reduced the number to below 10 000 for the first time in 50 years in 2009 – a reduction that continued to 7129 cases in 2010, 2800 in 2015 and now to its current level, which represents a 96% reduction during the past 20 years.
- The latest data show that only 980 cases were reported to the World Health Organization (WHO) in 2019, 663 in 2020
- Virtually no vaccines, or very few, against parasitic diseases like sleeping sickness
Tell me about Chagas disease and what parasite it is due to
Chagas disease- Trypanosome cruzi.
- Protozoan parasite transmitted by assassin bug (S. American)
- Host: Many reservoirs plus humans
- Symptoms: fever, headache, cardiac & digestive
- 6 -7 million (estimated) cases in 2012. 65 million at risk (WHO figures)
- In Columbia alone - annual cost of medical care for all patients with the disease was estimated to be about US$ 267 million in 2008.
Tell me about parasites change in behaviour- Toxoplasma gondii
Protozoan parasite: primary host – cats; intermediate host – rodents.
Infected mice have decreased aversion to cat urine & increased reaction time
This increases the chance of being caught by a cat and therefore complete the life cycle
Also infects humans (zoonosis)
Tell me about parasites changing their coats- African typanosomes
- Variant specific glycoprotein (VSG) on the outside of the parasite in the host
- As the parasitemia rises the host raises antibodies to the coat killing most of the parasites
- Some of the remaining parasites switch their coat protein and therefore evade the host immune response
Tell me about parasites suppressing the immune system- Brugia malayi
- Nematode that infects the lymphatic system causing elephantiasis
- Secretes an analogue of the mammalian cytokine - macrophage migration inhibitory factor (MIF) which mimics the host cytokine thus suppressing pro-inflammatory activation of macrophages
Parasites are the reason for sex
explain the red queen hypothesis- Host-parasite-evolutionary dynamics
In Lewis Carroll’s “Through the Looking Glass and what Alice found there” the red Queen notes that “it takes all the running you can do to keep in the same place”
Hosts are under huge selection pressure to evolve to evade / counter parasites
Parasites are under huge selection pressure to circumvent host
A continual “arms race” of adaptation & counteradaptation (running to keep in the same place).
The Red Queen argues that host-parasite coevolution favours sexual individuals because they produce offspring with a variety of rare genotypes. In contrast, parasites rapidly adapt to infect common asexual lineages and drive them down in frequency
Selective sweeps and negative frequency-dependent selection
Tell me about the red queen hypothesis between sex and parasitism
Morran et al. 2011 Caenorhabditis elegans and Serratia marcescens (bacterial pathogen). Rates of outcrossing over multiple generations.
Control – no infection
Evolution – infection with a fixed strain of S. marcescens
Co-Evolution – infection with co-evolving S. marcescens
Lots of mathematical modelling studies
Long term experimental studies limited due to time and cost
C. elegans and bacteria –relatively tractable lab studies
Turko et al. 2018 - water fleas (Daphnia longispina) and protozoan gut parasite Caullerya mesnili
13-year longitudinal study! Natural population in lake (“closed populations”) – biweekly sampling in summer, else monthly.
Daphnia – asexual with sporadic sexual
Parasite – seasonal
Enzyme and microsat markers to genotype through time and detect clonal turnover
How are parasites implicated in a “behavioural immune system”
A first line of defence before mounting a metabolic immune response (costly in resources).
- Grooming – to remove ectoparasites – helps social cohesion of the group
- Disgust – steer clear of potentially infectious material
- Initial suspicion of outsiders
- Physical attractiveness and mating behavior – male birds doing courtship dances show they are healthy
How are parasites implicated in a “behavioural immune system”
A first line of defense before mounting a metabolic immune response (costly in resources).
- Grooming – to remove ectoparasites – helps social cohesion of the group
- Disgust – steer clear of potentially infectious material
- Initial suspicion of outsiders
- Physical attractiveness and mating behaviour – male birds doing courtship dances show they are healthy
What are the politics of parasitism?
- Human parasitology primarily a problem in underdeveloped regions
- Costly and protracted development of drugs and vaccines (very few)
- Logistics of health care delivery in underdeveloped regions
- Parasites have very complicated life cycles, drug resistance, complex and multi-approach integrated control strategies
- Animal reservoirs
- Vectors
- Not high on the agenda of western governments unless it affects their population (e.g., malaria affecting US troops) – but this may change
