Exam 3 IDS2935

Exodus

Plagues of egypt

The Black Death

Killed over 50% of the European population in a two year period (1348-1350)

Napoleon's Army

Yellow Fever wiped out Napoleon's army, lost the war

Medical (public health) entomology

Focuses on insects and arthropods that impact human health

Veterinary entomology

Focuses on insects and arthropods that impact animal health

Military entomology

Majority of casualties are caused by arthropods in most conflicts (Napoleon in Haiti and Russia for example); includes scientific research on behavior, ecology, and epidemiology of arthropod disease vectors. Involves public outreach.

Diseases in battle

Malaria, Dengue, Lymphatic filariasis, Sandfly fever, Scrub Typhus, Leishmaniasis

Reasons for vector borne illness increase

Globalization, climate change, new detective technology, increased attention/awareness, no control measures previously

Top infectious threats to the military today

Malaria, Dengue, Leishmaniasis

Integrated Pest Management (IPM)

A sustainable approach to managing pests by combining biological, cultural, physical, and chemical tools in a way that minimizes economic, health, and environmental risk

Goal of IPM

Achieve satisfactory control of pest populations using the least toxic methods possible

Human Flea (Pulex irritans)

Transmits plague (Yersinia pestis) and Murine Typhus (Rickettsia typhi)

Sandfly (Genus Phlebotomus)

Vectors Leishmaniasis and Sandfly fever

Leishmaniasis

symptoms:

• Cutaneous (Leishmania tropica/major): sores on skin
• Mucocutaneous: in nose and mouth
• Visceral (Leishmania donovan): on organs --> causes fever, weight loss, anemia, swelling of spleen/liver, death

Sandfly prevention

Insect repellent and bet nets

Stockholm Convention

Sought to protect human health and the environment from persistent organic pollutants (such as DDT); aimed to reduce/eliminate DDT but was decided against because of its benefits for vector control (WHO recommends DDT residual spraying for Malaria)

Pest

Any organism that is harmful to humans or things of human concern such as plants, animals, and micro-organisms

Pesticide

Substances/mixtures used in agriculture or public health programs to protect against pests; can be chemical or biological but must deter, incapacitate, kill, or otherwise discourage pests from causing damage

Nematicides

Pesticide that targets nematodes (lymphatic filariasis)

Acaricides

Pesticide that targets mites and ticks

Insecticides

Pesticide that targets insects

Insecticides

Pesticides formulated to kill, repel, or mitigate the effects of insects; control of insect pests benefits crops and controls vector-borne diseases --> saving millions of human and animal lives; the most important element of integrates approach to vector control

Classification of Insecticides

• Chemical composition
• Mode of Entry
• Mode of Action
• Toxicity
• Stage specificity

Chemical composition

4 types of composition

• Organic
• Inorganic
• Pyrethrum (from Chrysanthemum flowers)

Organic insecticides

Have carbon as the basis of their molecular structure

Inorganic insecticides

Crystalline, environmentally stable, do not contain carbon, usually derived from mineral ores extracted from the earth; example: copper, sulfur, mercury, boron

Pyrethrum

Product extracted from the flowers

Pyrethrins

Actual active ingredients in the Pyrethrum

Pyrethroids

synthetic compounds produced to mimic the effects of Pyrethrin that

Mode of Entry

• Contact poison
• Stomach poison
• Fumigants

Contact poisons

An insecticide whose mode of entry is capable of gaining entry into the insect body through the cuticle; ex. DDT

Stomach poison

An insecticide whose mode of entry is through the mouth or digestive system of the insect when ingested; ex. lead arsenate

Fumigant

An insecticide whose mode of entry is through the spiracles. Volatile chemical compounds enter the bodies of insects in a gaseous phase; ex. Methyl bromide, napthalene

Mode of Action

Insecticides that target ion channels, enzymes, receptors and produce action

DDT/Pyrethroids

Insecticide opens the sodium ion channel in the neurons. The pyrethroid block the closure of the channel, causing repetitive firing which induces spasms and eventually death in the insect (inhibitor is blocked)

Organophosphates/ Carbamates

Inhibit acetylcholinesterase which catalyzes the breakdown of acetylcholine (a neurotransmitter at nerve junctions)

Bt insecticides

Chemicals produced by natural Bacillus thuringiensis bacteria that kill insects in their larval stage; targets the midgut of the insect where it lyses the midgut epithelial cells. This results in loss of midgut integrity and ultimately death of the insect

Neonicotinoids

Chemicals related to nicotine that mimic acetylcholine and make insects jumpy with leg tremors, rapid wing motion, disoriented movement, paralysis, and some cause death. Imidacloprid is an example of this.

Insect Growth Regulators (IGRs)

New chemicals that mimic hormones in young insects that interfere with the normal growth or development of the pest

• Chitin synthesis inhibitors (ex. diflubenzuron) <-- chitin is the hard shell that protects insects. The inhibition of this would cause improper growth and insufficient protection of the organism and thus more susceptible to death
• Nuclear Hormone Receptor
  Juvenoids/ Juvenile hormone analogs (ex. methoprene)
  Ecdysone (plays a big role in coordinating developmental transitions such as molting) interference

LD50

(Lethal Dose 50%); the amount of a substance, given all at the same time, which causes the death of 50% of the organisms in the dose group; one way to measure short-term poisoning potential (acute toxicity) of a material

Ovicide

Insecticide that targets eggs

Larvicides

Insecticide that targets larval stages

Pupicides

Insecticide that targets pupal stages

Adulticides

Insecticide that targets adults

Benefits of insecticides

• Reduction of nuisance and annoyance
• Protection and enhancement of lawns, gardens, parks, and ponds for public enjoyment
• Protection of pets
• Control of invasive pests that may vector disease
• Control of vector-borne diseases (ex. Onchocerciasis with larvicides and Chagas with pyrethroids)

Problems with insecticide usage

• Kill insects and other unintended organisms that share biochemical pathways with insects; human exposure --> can kill beneficial insects such as honeybees and natural biocontrol agents
• Acute (rash, blisters, stinging eyes, diarrhea, nausea, death, blindness) or chronic (cancer, birth defects, reproductive harm, disruption of endocrine system, etc.) effects --> children, farm workers, and insecticide applicators are most susceptible
• Secondary pest outbreaks
• Disturb soil arthropods
• Pest resurgance
• Bioaccumulation and biomagnification
• Resistance

Insecticide resistance

Selection of a heritable characteristic in an insect population that results in the repeated failure of an insecticide product to provide the intended level of control when used as recommended; rapid development of resistance is due to genetics and intensive application

Behavioral resistance

Resistant insects may detect or recognize a danger and avoid the toxin

Reduced penetration resistance

Resistant insects may absorb the toxin more slowly that susceptible insects

Metabolic resistance

resistant insects detoxify/destroy toxins faster than susceptible insects or quickly rid their bodies of the toxic molecules; most common
ex. enzymes: cytochrome P450, monooxygenases, estrases, glutathione-S-transferases

Altered target-site resistance

The site where the toxin usually binds inside the insect becomes modified to reduce the insecticides effects; second most common

Cross resistance

When insects that exhibit resistance to one insecticide are also resistant or develop resistance more rapidly to other insecticides with the same mode of action; ex. houseflies resistant to DDT are also resistant to pyrethroids without any previous exposure because DDT and pyrethroids have the same mode of action

Multiple resistance

When several different resistance mechanisms are present simultaneously in resistant insects. The different resistance mechanisms may combine to provide resistance to multiple classes of products

Rotation

The best strategy for controlling disease vectors is the rotational use of insecticides with different modes of action altogether

Mixtures

The theory is that if resistance to each of the two insecticide compounds within a mixture is rare, then multiple resistance to both will be extremely rare. For this to work well, both insecticides need to be used at their full operational target dose and the efficacy + persistence of the two insecticides should be broadly similar

Fine-scale mosaic

Spatially separated applications of different compounds against the same insect
ex. using pesticide x in one house and pesticide y in a different house in the same village <-- will reduce the rate of resistance selection since there are multiple things to select

DDT

• First modern synthetic insecticide in the 1940s
• Initially used to combat malaria and typhus in military and civilian populations
• Effective in insect crop control, gardens, homes, etc.
• Assisted in malaria eradication in the U.S.
• DDT revealed to have declining benefits in the environment and toxicological effects
• Silent Spring (Rachel Carson) stimulated widespread public concern over the dangers of improper pesticide use and the need for better pesticide control
• Persistent in the environment
• Accumulates in fatty tissues
• Can travel long distances in the upper atmosphere
• Discontinued in the U.S.
• Used in African countries via residual spraying

Antigen

A toxin which induces an immune response in the body, especially the production of antibodies. Antigens are targeted by antibodies

Adjuvant

Ingredient used in some vaccines that helps create a stronger immune response in people receiving the vaccine; help vaccines work better as they enhance the body's immune response to the antigen

Antibody titer

Measurement of the level of antibodies in a blood sample; measures how much a sample can be diluted before antibodies can no longer be detected

Transmission blocking vaccines (TBV)

Administered to the vertebrate host to produce antibodies that will later block the pathogen in the vector, making it unlikely to transmit it to a new host; none available at the moment

Classic vaccines

most currently available; designed to induce immune responses that will protect the host from suffering the disease after exposure to an infective bite

Live-attenuated vaccines

Use a weakened form of the disease-causing pathogen

• most common for bacteria or viruses
• excellent immune response
• sufficient time for memory cell production (continual antigenic stimulation)
• ex. Yellow Fever vaccine

Inactivated vaccine

Made from the pathogen that has been killed through heat, radiation, or chemical processes

• no risk of inducing disease as there are no live components
• weaker immunity than attenuated vaccines; may require boosters
• ex. Polio, Hep A, rabies

Subunit/Recombinant/Polysaccharide/Conjugate vaccine

Do not contain live components of the pathogen, only the antigenic parts that are necessary to elicit an immune response

• very strong immune response that targets key parts of the germ
• may require boosters
• ex. Hep B

mRNA vaccines

Teaches your body to make proteins. When your body recognizes these proteins, your body jumpstarts antibody production (= immune response)

• ex. Covid-19

Toxoid vaccines

Based on the toxin produced by the pathogen; toxins invade the bloodstream and are largely responsible for the symptoms of the disease. The protein-based toxin (toxoid) is harmless and are used as antigens to elicit immunity

• ex. Diphtheria, Tetanus

Transmission-blocking vaccines (TBV)

Administered to the vertebrate host to induce an immune response that will later block pathogen development in the arthropod vector during or after blood feeding; antibodies target proteins exposed on the parasite surface in the mosquito midgut and mosquito salivary components that are involved in pathogen development

• lack of vector competence
• blocks the spread of disease-causing organisms

Important features of developing a TBV

• candidate molecule should be critical for vector-pathogen interaction. Disruption of the candidate molecule should affect acquisition/transmission/replication of the pathogen inside the vector
• candidate molecule should provide high antibody titer upon injection into humans to block pathogen transmission from vectors
• candidate molecule should be compatible with different adjuvants to effective induce immune response in humans
• candidate molecule should not result in exaggerated immune responses leading to immune-related disorders in humans

Specificity

targets a single insect pest species, is chemical free, and could reduce the need for insecticides overall

Comprehensive coverage

populations of vector species that are inaccessible to existing control methods could be controlled using the ability of the males to find females

Equity

will protect