Terms in this set (62)
How many species are there on Earth and in the Ocean?
86% of species on earth and 91% in the ocean are yet undescribed. Insects represent ~75% of all animal species.
Science of classifying organisms.
The system currently used by taxonomists is called the Linnaean taxonomic system. Binomial. Genus and species.
Insect classification-fire ants
-Family: Formicidae- family suffix "dae"
Arthropoda has 5 sub-phylums
triblobita, myriapoda, hexopoda, chelicerata, crustacea.
Characteristics of Arthropods
-Metamerism or segmentation
-Tagmosis - segments fused into regions
-Jointed paired appendages
-Exoskeleton and Molting
-Complex Movement and Locomotion
-Nervous system - dorsal brain and ventral nerve cord
-Adapted for land, water, and air
-Well developed sense organs
Arthropods divided into two main groups based on mouth parts
- Chelicerae (Chelicerata) and mandibles (Crustacea, Hexapoda,Myriapoda).
How Are Insects Different From Other Arthropods?
-3 tagmata or body regions: head, thorax, and abdomen
-3 pair of legs with great variety of types: running, raptorial, digging, swimming, etc.
-Both compound and simple eyes- all other arthropods only have simple eyes.
-Many have wings
-Highly variable mouthparts: chewing, piercing-sucking, lapping, etc.- mouth parts determine the type of parasite/disease that is transferred.
Insecta- 2 main groups
Pterigota (winged) and Apterigota (wingless)
-Apterigota- do not have wing pads.
Pterigota- 2 main orders
Paleoptera (mayflies, dragonflies) and Neoptera can fold wings back- this order has 99.17% of insects.
Neoptera has two groups- Exopterigota, Endopterigota.
Exopterigota or Hemimetabola
-Insects undergo incomplete metamorphosis
-Immature stages are called "nymphs" that transform directly into the adult without a pupal stage.
-Wing pads developing externally.
Endopterigota or Holometabola
-Insects undergo complete metamorphosis.
-Immature stages are called "larvae" that transform into the adult with a pupal stage.
-Wing pads developing internally inside the pupa.
The Classes of Arthropods
Subphylum-Crustacea- 8 pairs of legs. 2 pairs of antennae
-Centipedes- have 2 stingers at the end of tail that can be venomus and can eat other insects. 1 pair of legs for each segment
-Millipedes- herbivores- 2 pairs of legs for each segment
Benefits of hematophagy
-Exploited by parasites quickly
For the parasite:
-Rich source of nutrients
-Increases mobility by feeding on other animals
-Ability to find novel hosts
-For the vector:
-parasite can modify the behavior of the host to increase their survival, they can drive the vector to find a new host
Strategies that have evolved in hematophagous insects
-Host (vertebrate) location cues- finding meal
-Proximal blood location- where to feed
-Digesting the blood meal
-Three strategies for location of vertebrate hosts:
-Long distance host location
-Eg. Mosquitoes and other flies
-Proximal host location- insects that always need a host to survive.
-Eg. Lice, some flea, ticks
-Intermediate host location-
-Eg. Fleas, bed bugs
Host location cues
-Use visual cues to locate hosts.
Eg. Mosquitoes prefer dark colors on which to land.
-Odors acts as signal as well.
Eg. CO2, water vapor from breath and lactic acid can attract insects.
-Heat sources guide nocturnal feeders towards their host.
-Other cues such as circadian cycles.
Eg. Anopheles is a night-biter whereas Aedes is crepuscular (dawn and dusk)
-Once an arthropod has landed on the skin of its host different cues are used to locate blood
-Aedes- probes repeatedly at 7 second intervals to find the ideal spot.
-Mechanoreceptors at the tip of the mouthpart or antennae test for "tastiness".
-Other species of mosquito usually feed on birds but can feed on mammals although it takes longer to find a host.
-Arthropods have modified their mouthparts in a wide variety of ways to enable hematophagy.
Two main strategies:
-Telmophagy or pool feeding- ticks, sand flies
-Solenophagy or capillary feeding- mosquitoes.
Development of blood feeding habits: telmophagy
A prolonged and close association between hosts and arthropods that regularly fed on dead parts of the host's body or organic debris associated with the nests or burrows may have gradually established more profound parasitic relations by switching to a hematophagy.
Development of blood feeding habits: solenophagy
The development of hematophagy would have been facilitated by morphological preadaptation of their ancestors to phytophagy or entomophagy (other insects)
Types of mouth parts-Mandibulate-
-Used to masticate (cut, tear, crush, chew) food items. Various modifications.
-Eg. Tick, grasshopper
Types of mouth parts-Suctorial-
Range of modifications exists. These mouthparts pierce food items and suck the internal fluids through a tubular organ
Hematophagy evolution in Hemiptera-- Chagas bug-
-The most primitive hematophagous insects belonged to Hemipteran order.
-Most hemipteran bugs feed on plants using piercing-sucking stylets.- tube like mouth parts
- mouthparts have a saliva tube and a food tube before the long one. No mixing of food and saliva
Hematophagy evolution in Phthiraptera. -Hematophagy next arose in the lice order
There are two main suborder of lice
-Chewing lice Eg. Chicken body louse
-Sucking lice Eg. Head louse
-Stylets in lice lie in a sac concealed within the head. Inside instead of outside like the bugs.
-Similar to Hemipteran mouthparts
Hematophagy evolution in Siphonaptera
-Hematophagy next arose in the flea order.
Flea also possess solenophagous mouthparts. Two sawlike laciniae cut the skin. The epipharynx is like a needle. The laciniae surround the epipharynx, and together they form the stylet, or puncturing organ.
-Hematophagy arose independently many times during the evolution of flies.
Two Diptera suborders:
-Nematocera (thread horn) Eg. Mosquitoes- more primitive
-Brachycera (short horn) Eg. house flies
Hematophagy in Diptera
-Four main hematophagous families
-Black flies (River blindness)- telmophagy
-Biting midges (Filarial worms)- solenophagy
-Sand flies (Leishmaniases)- telmophagy
Flies and mosquitoes only have 1 canal.
Several hematophagous families
-More primitive ones (horse flies) have coarse blade like stylets for telmophagy.- pool feeding
-Advanced brachycerans (Tse-tse fly) have mouthparts modified for solenophagy.- capillary feeding.
Hematophagy evolution in Lepidoptera
-Most Lepidoptera have long coiled sucking tube or proboscis to suck nectar.
-Hematophagous leps probably arose from fructivorous lepidoptera.
-The proboscis have sharp tearing hooks at the tip. E.g. Noctuid moths
Hematophagy evolution in Chelicerata
-Arachnid ancestors always possessed piercing-sucking mouthparts or chelicerae.
-Acari or ticks possess highly sclerotized structure called hypostome- drill with inverted hooks.
-Mites and chiggers have movable stylets or hooks.
Insect salvia acts as a anticoagulate and a "numbing" solution
-Host cellular and molecular response that prevents blood loss from a damaged vessel through several redundant processes
-Blood vessel vasoconstriction, formation of a primary platelet plug (primary haemostasis)
-Vessel strengthening by blood coagulation (secondary haemostasis)
Digesting the blood meal
-Once the blood meal is ingested it travels to the gut.
-Once the bolus reaches the mid-gut, digestive enzymes are secreted. Eg. Trypsin (early digestion)
-Further digestion by amino-and carboxypeptidases.
-Blood is rich in proteins and essential amino acids, but deficient in carbs, fats, and vitamin Bs.
-All blood-feeding insects have bacterial endosymbionts that supplement the blood dietary deficiencies.
-An endosymbiont is any organism that lives within the body or cells of another organism forming symbiosis.
-Two types-Primary (P) and Secondary (S) endosymbiont.
-P-endosymbiont convert protein to carbs
-P-endosymbionts, Buchnera in aphids synthesize essential amino acids Wigglesworthia in tse-tse fly synthesize vitamins. S-endosymbiont confers protection against ecological stresses.
-Eg. Wolbachia- drives its host insects to all be females, one consequence is shorting lifespan.
-Once arthropods have ingested large amounts of blood, locomotion and flying becomes difficult.
-So, they eliminate water from blood meal to reduce weight.
-The volume of blood ingested is regulated by stretch receptors in the gut.
---Fifth instar rhodnius weighing 30mg can ingest 300mg of blood and urinate 150mg in 6 hours.
Basic vector borne disease cycle:
Vector-> host with disease transferring between the two.
Vectors: The 9 orders of insects
Hosts: Mammals, birds, reptiles, amphibians
Pathogens: Protozoa, virus, bacteria
Parasite maintenance and amplification
-Maintenance = is the long-term survival of the pathogen by transmission between vertebrate hosts and vectors.
-Amplification = occurs with the onset of resumed and/or increased transmission and compensates for the previous loss- this happens in the host.
Bad host-parasite example
when the host is not susceptible to the stage of development the host is needed for the parasite.
-Humans are not susceptible to the larval stages of bird schistosomes (flatworms).
-These parasites are quickly killed off, the associated inflammation & itching is called cercarial dermatitis (or 'swimmers itch').
-In the natural duck host, larval stages develop into established infection with adult worms.
Good host-parasite example
-Parasites of major medical & veterinary importance successfully adapted to innate & acquired immune responses of host. E.g. malaria (Plasmodium spp.)
-Susceptibility of a host to a given parasite can depend genetic background, age, nutritional & hormonal status etc. of an individual.
Benefits of hematophagy
Exploited by parasites quickly
For host parasite and vector
-rich source of nutrients
-increases host availability
-The relationship between virulence and fitness of arthropod-borne viruses in vector has not been evaluated.
-The interaction is largely thought to be benign, but some costs of arbovirus exposure have been identified for mosquitoes. For eg. Reduced fecundity and survival of Culex-WNV system
Surviving in vertebrate hosts
-In the vertebrate host, viremia (virus in the blood) must be high and must be for long duration for vector infection.
-In "good" host-pathogen relationship, the pathogen must not kill the host too soon!
Surviving in the vector
-In the vector, the pathogen must infect and replicate in the vector.
-They can also be present on the outside of the body, may be on/around mouth parts.
-The pathogen may cause LITTLE OR NO deleterious effect on the vector.
-The pathogen may manipulate vector behavior to increase transmission
Arthropod vector characteristics
--Four criteria to be considered a primary vector
1. The vector must associate and feed on the vertebrate host under field conditions
2. Naturally infected vectors must be recovered from the field.
3. The vector must be shown to become infected by feeding on a viremic host.
4. The ability of an infected host to transmit the parasite to a new vertebrate host should be confirmed under controlled conditions.
a vector that can transmit a pathogen from a viremic host and spread from there.
Modes of transmission
-Two main types
-Horizontal- occurs because of a common host. Or mating
-Vertical- parent to offspring- virus
-The parasite's ability to reproduce or develop in the arthropod vector before being transmitted to the vertebrate host.
-Three modes of parasite development
-Cyclopropagative- the parasite undergoes developmental changes but not multiplication of the parasite E.g- virus, riskettsia, bacteria
-Propagative- the parasite multiplies but does not undergo developmental changes. E.g- filaria
-Cyclodevelopment- both developmetal changes and multiplication. E.g-protozoans
Horizontal vs. vertical
Vertical transmission occurs only in biological type.
-Eg. Flaviviruses such as WNV, dengue
-Horizontal transmission occurs both in mechanical and biological type.
-Eg. via infected host, or mating
-The parasite does not reproduce or develop in the arthropod, but is transmitted physically often through mouthparts of a contaminated arthropod.
-Transmission is possible only for a short period of time, not very efficient
-Most hematophagous arthropods could transmit parasites mechanically.
-Is the intrinsic ability of a vector species to biologically transmit a disease.
-Any trait, such as, host feeding preferences or susceptibility to pathogen infection, that has genetic component will affect vector competence.
Barriers to biological transmission
-In any vector-parasite system, there are multiple (6) barriers to productive vector infection.
-The most important of these are at the mid-gut, salivary gland, and ovaries.
1st barrier-Mid-gut infective barrier- must be able to establish an infection in the midgut epithelium, and replicate.
Midgut escape barrier- must pass through basal lamina and replicate in other organs
Transmission barrier- infection of salivary glands, and escape into the lumen of the salivary glands
-This entire process which takes several days to complete in the mosquito is called the extrinsic incubation period (EIP).
Genetics of vector competence
-Additional barriers to vector competence includes-
-arthropod digestive enzymes and digestive processes
-intracellular processes and the arthropod's immune system
-It is widely appreciated that arthropod genetic factors and the environment both influence vector competence.
-Factor controlling midgut infection
-Trypsin and Serine protease enzymes (MG barrier)
-Presence of specific midgut epithelial receptor that binds to Dengue (Curiel et al. 2008)
-Insect immunity genes
-Janus kinase-signal transducer and activator of transcription (JAK/STAT) and Toll pathways, immune deficiency (IMD) and RNA interference (RNAi) machinery
-Overall ability of a vector species in a given location and time to transmit a parasite i.e., number of infectious bites a person receives.
Although it is a simplified model, it has been very helpful in understanding the critical components of the life cycle of pathogens and their relative contributions to their transmission and maintenance in nature.
- The most often studied environmental factor influencing vector competence for arboviruses is temperature
effects both parasite and vector development.
- Eg. increases virus replication in vector
-Other factors include PH and humidity
- Nutrition and competition during the larval stage may also influence the subsequent vector competence as adults
-Vectors are usually inactive during winter in the temperate regions or dry seasons in the tropics.
-In the temperate regions, arthropods undergo diapause where as they go into estivation (hibernation in hot temperatures).
-Parasites persist in the stage that remains dormant
-Parasites persists in eggs or nymphal stages during dormancy
-Parasites persists in an undetected arthropod vector when the vector is inactive
Reservoirs of infection
-Principal habitat where a specific parasite lives and multiplies and from which it may spread to cause disease.
-Vertebrate hosts are generally considered reservoir hosts, but these reservoirs are rarely identified.
Reservoirs of infection-Humans
-Human reservoirs may or may not show illness. Eg. Typhoid Mary- asymptomatic
-Humans are also subject to diseases that have animal reservoirs.
-The term zoonosis refers to an infectious disease that is transmitted from vertebrate animals to humans.
-Eg. Anthrax, rabies etc. More recently, SARS, HIV
-Plants, soil, and water in the environment are also reservoirs for some infectious agents.
-Eg. Many fungal agents, such as those that cause histoplasmosis, live and multiply in the soil.