Medicinal Entomology Midterm

entomology

from the Greek "entomon" meaning "cut up or divided into segments"

3 basic characteristics of arthropods

jointed appendages, segmented body, external skeleton

Types of problems caused by arthropods

• Annoyance/nuisance

• Toxins and Venoms

Diseases caused by arthropods

• Disease: Destruction of host tissues

• Called "myiasis" when done by fly larvae

• Disease = vector-borne diseases

• Disease = Food contamination

• Disease = Allergic reactions

• Disease = Psychological stress

• Fear

• Delusional disorders (eg. Morgellons disease)

Mosquito

The most dangerous animal. Kills 725,000 people a year

Malaria

Vector borne disease from mosquitos. Kills 600,000 a year

Koch's postulates (1884)

Germ theory of disease versus Miasma theory

Patrick Manson

Founder of the tropical medicine field

Role of mosquitoes inhuman elephantiasis (1877)

Theobald Smith

Discovered the causative agent of Texas cattle fever was vectored by the cattle tick.(1893)

Ronald Ross

Described the life-cycle of the parasites of malaria (1897)

Walter Reed

Demonstrated the role of Aedes mosquitoes in the transmission of yellow fever. (1900)

William Burgdorfer, Alan Barbour, Jorge L. Benach

Discovery of the agent of Lyme Disease (1982)

Koch's Postulates

a sequence of experimental steps for directly relating a specific microbe to a specific disease

Vector-borne diseases

Diseases transmitted by vectors like mosquitoes.

Vector

an organism, typically a biting insect or tick, that transmits a disease or parasite from one animal or plant to another.

mechanical vector transmission

picks up an infectious agent on the outside of its body and transmits it in a passive manner

biological vector transmission

pathogens are within the vector and transmission to the host is through a bite (ex. plague)

Propagative transmission

parasite multiplies within the vector without any cyclical changes (parasite increases in number within the vector but does not undergo any developmental changes)

Cyclodevelopmental transmission

The parasite undergoes cyclical changes within the vector but does not multiply, i.e., there is only developmental changes of the parasite without multiplication.

Cyclopropagative transmission

The parasite undergoes cyclical changes and multiplies within the vector, i.e., there are both developmental changes and multiplication of the parasite

Four criteria used to identify primary vectors

1. associate and feed on the reservoir and its seasonality should coincide with the incidence of vertebrate infection

2. be commonly found infected with the disease agent

3. be shown to become infected experimentally

4. be shown to be capable of transmitting the disease to an uninfected host

vectorial capacity

equation that accounts for the major factors of pathogen transmission by mosquitoes and is defined as the average number of new vertebrate infections per day resulting from an initial index case

V=ma^2 p^n / - ln (p)

The ratio of mosquitoes to humans ( m ); human biting rates ( a ); mosquito survival through one day ( p ); pathogen latent period (n days)

4 components vectorial capacity depends on

1. number of mosquitos

2. feeding frequency and type

3. survivorship

4. vector competence

bridge vector

organism that transmits a pathogen from one animal host to a human

Enzootic vector

organism, typically a biting arthropod, that transmits a pathogen from one animal host to another

Risk (probablity) of human infection

endemic disease

disease constantly present in a population

epidemic disease

is the rapid spread of disease to a large number of patients among a given population within an area in a short time.

pandemic disease

an epidemic disease that occurs worldwide

Enzootic

an endemic disease present in an animal population, no humans

epizootic

is the rapid spread of disease to a large number of patients among a given population within an area in a short time.

Invasive mosquitos

Are the drivers of most recent epidemics of mosquito-borne diseases (Culex, Aedes)

Mosquito-borne diseases

òYellow fever

òDengue (DHF)

òWest Nile encephalitis

òRift Valley fever

òChikungunya

òZika fever

òUrban malaria

parts of the mosquito

head, thorax, abdomen

Mosquito Taxonomy

Kingdom: Animalia

Phylum: Arthropoda

Class: Insecta

Order: Diptera

Family: Culicidae

Subfamily: Anophelinae or Culicinae

mosquitos

38 genera organized in 11 tribes, 3500 species

Morphological differences between Anophelinae and Culicinae in relation to the stages.

Anopheles gambiae

malaria and human filariasis

Culex pipiens

West Nile, bird malaria, St. Louis encephalitis

Aedes spp.

denge, yellow fever, Zika, chikungunya

Aedes aegypti

yellow fever mosquito

Aedes albopictus

Asian tiger mosquito

Anthropophilic

Preferring or seeking a human host over another animal. Supplement. The term anthropophilic is used to describe parasites that prefer or seek human as host rather than other animals.

Endophilic

having an attraction to or preference for indoor environments

endophagic

feeds indoors

Mosquito eggs

Culex: no floats (laid in rafts on water)

Aedes: no floats (laid beside water)

Anopheles: Lateral floats (laid on water)

Anopheles morphology

Rest parallel to water surface (no siphon)

Aedes & Culex morphology

Rest at angle to water surface (siphon)

mosquito life cycle

egg, larva, pupa, adult

Aedes aegypti

tropical invasive mosquito (expanded worldwide after 1500s)

Aedes albopictus

Expanded worldwide after 1960s, tropical and temperate invasive mosquito

Aedes japonicus japonicus

(expanded worldwide after 1990s) temperate invasive mosquito

Phylum Arthropoda

largest phylum in the animal kingdom

Arthropod characteristics

•Exoskeleton (hardened plates with flexible joints) made predominantly of chitin (a nitrogenous polysaccharide = polymer of n-acetyl-glucosamine)

•Articulated appendages

•Segmentation

•Open circulatory system

•Hemolymph

•Specialized excretory structures, Malpighian tubules.

Exoskeleton

an external skeleton that supports and protects an animal's body.

1. Protection against predator

2. Support: it provides an attachment framework for muscles.

3. Protects against desiccation.

Ecdysis

periodic shedding of the cuticle in arthropods

cuticle of arthropods

Outermost portion of the animal (exoskeleton) made of proteins and calcium; secreted by underlying cells and periodically molted during growth.

exuviae

shed exoskeleton

Epicuticle

The outermost layer of the insect cuticle designed to prevent water loss.

Procuticle

inner thick layer of an arthropod shell that consists primarily of layers of protein and chitin

diatomaceous earth

fossilized remains of diatoms, a type of hard-shelled microalgae

hemolymph

has the same functions of the vertebrate blood and lymph combined (except that oxygen reaches cells through the tracheal system - CO2 dissolves and is excreted by the Malpighian tubes). Also acts as a physical force (hydraulic) to extend proboscis, reproductive organs, molt.

hemocytes

wound repair, detoxification, immunity

Ametabolous

undergoing slight or no metamorphosis

Hemimetabolous

Incomplete metamorphosis where the immature resemble the adults but some features are missing or different (wings, reproductive organs, color, shape, etc.). no pupal stage.

Holometabolous

Complete metamorphosis; egg, larva, pupa, adult

telmophagous

pool feeders

solenophages

Penetrate capillaries & feed directly

Myiasis

infestation by larvae of flies usually through a wound or ulcer

two main fly families that cause myiasis

Calliphoridae (blow flies) and Muscidae (House flies, Stable flies)

Pseudomyiasis

- Accidental myiasis.

- Dipterous larvae found in the GI of man or animals which have been accidentally ingested with food or water.

- Normally no pathological manifestaions.

Sacrophagidae

flesh flies

Facultative myiasis

can eat either dead or living flesh; opportunistic

primary myiasis

species that can initiate myiasis

secondary myiasis

species that invade already compromised tissues

tertiary myiasis

species that join primary and secondary species just prior to host death

Obligatory myiasis

completely parasitic dipteran fly larvae; require a living host; always parasitic

Temporary myiasis

intermittent contact between a fly larva and host

Incidental Myiasis

Occasional parasitism of atypical

hosts by obligate myiasis-producing flies

" Cattle grubs on horses, sheep nose bot in humans

Human myiasis

relatively uncommon; not suitable hosts

gastrointestinal myiasis

Ingestion of eggs or maggots from infested food can result in general malaise, nausea, vomiting, cramps and diarrhea.

Wound myiasis

Deposit of larvae in suppurating wound; larvae maybe visible on wound; people living on farms are at higher risk

Ophthalmic Myiasis

The most common form of human myiasis. It is generally caused by a sheep nose bot when a gravid female oviposits into an eye while hovering

Calliphoridae

blow flies, carrion flies

Cochliomyia hominivorax

Screwworm fly; present in New World tropics. Infestation serious and fatal. Affects warm-blooded animals and eats healthy tissue

life cycle of screwworm

Gravid females are attracted to fresh open wounds on any warm-bodied animal.

•Each female deposits 100-200 eggs (up to 1,000/female lifetime)

•Females feed at the wound to obtain extra protein/lipids

•After 10-20 hrs eggs hatch

•Maggots develop in 4-12 days, then drop to the ground and pupate

•After 1-week adults hatch, mate, and in a few days, look for hosts

•Entire cycle (egg to egg) takes 2-3 weeks

Dermatobia hominis

tropical or human bot fly; pest of cattle, humans, dogs and monkeys

Myiasis treatment

petroleum jelly, antiseptic and protective dressing

Edward Knipling

Idea of screwworm eradication program.

Screwworm eradication program

Sterile male technique was developed and championed by screwworm researchers. First successful field test was achieved with the eradication of the primary screwworm

Sterile Insect Technique

the release of large numbers of sterilized males to mate with wild females and prevent the fertilization of eggs and production of viable young. Not self-replicating

Basic Principles of SIT

•Swamp the pest population with "treated" males

•Treated males mate with wild females and

•There is no offspring - sterile mating

•The female offspring die/are flightless

•Due to lack of reproduction or lack of females, the vector population crashes

or

•Due to low transmission, parasite populations crash

Ways of creating a "sterile" male

•Radiation – (x-rays, gamma rays – IAEA)

•Genetic manipulation (RIDLTM = release of insects carrying a dominant lethal)

•Infection with incompatible Wolbachia intracellular bacteria (rickettsia)

RIDL

•It is a control strategy using genetically engineered insects that have (carry) a lethal gene in their genome (an organism's DNA).

•RIDL males and females are released to mate with wild males, and their offspring die when they reach the larval or pupal stage because of the lethal gene.

Wolbachia

a genus of bacteria which infects arthropod species, including a high proportion of insects, as well as some nematodes. It is one of the world's most common parasitic microbes and is possibly the most common reproductive parasite in the biosphere

cytoplasmic incompatibility

a phenomenon that results in sperm and eggs being unable to form viable offspring. The effect arises from changes in the gamete cells caused by intracellular parasites like Wolbachia, which infect a wide range of insect species; mosquito population control mechanism

Life cycle of Aedes mosquito

•Aedes mosquitoes have 4 life stages

•They can reproduce inside and outside the home

•Life cycle takes 8-10 days

Aedes mosquito eggs

• Adult female mosquitoes lay their eggs on the inner, wet walls of containers with water above the waterline.

• Mosquitoes generally lay 100 eggs at a time.

• Eggs are very hardy; they stick to the walls of a container like glue and can survive drying out for up to 8 months—even over the winter in the southern United States.

• It only takes a very small amount of water to attract a female mosquito. Bowls, cups, fountains, tires, barrels, vases, and any other container storing water makes for a great "nursery."

Aedes mosquito larvae

•Larvae emerge from mosquito eggs, but only after the water level rises to cover the eggs. This means that rainwater or humans adding water to containers with eggs will trigger the larvae to emerge.

•Larvae feed on microorganisms in the water. After molting three times, the larva becomes a pupa.

Aedes mosquito pupa

•Pupae will develop until the body of the newly formed adult flying mosquito emerges from the pupal skin and leaves the water.