5 - vector borne diseases

What is a vector borne disease?

a disease that requires a vector for transmission

What phylum are most vectors?

arthropods

List 4 generalised methods of treating the infected person

• vaccines

• medicines

• hygiene

• public health information

List 3 generalised levels that vectors can be treated

• ecological

• organismal

• molecular

What are a combination of treatments on multiple levels called?

IVM - integrated vector management

List 8 vectors

• mosquitoes

• aquatic snails

• culicoides flies

• blackflies

• fleas

• sandflies

• ticks

List 3 genus of mosquitoes

• Ades

• Anopheles

• Culex

List 3 diseases transmitted by Ades mosquitoes and what kind of pathogen each are

• lymphatic filariasis - nematode

• rift valley fever - virus

• zika - virus

List 3 diseases transmitted by Anopheles mosquitoes and what kind of pathogen each are

• lymphatic filariasis - nematode

• malaria - protozoa

• O’nyong’nyong virus

List 3 diseases transmitted by Culex mosquitoes and what kind of pathogen each are

• japanese encephalitis - virus

• lymphatic filariasis - nematode

• west nile fever - virus

List a disease transmitted by aquatic snails and what kind of pathogen causes it

schistosomiasis - trematode

List a disease transmitted by culicoides flies and what kind of pathogen causes it

oropouche fever - virus

List a disease transmitted by blackflies and what kind of pathogen causes it

onochocerciasis (river blindness) - nematode

List a disease transmitted by fleas and what kind of pathogen causes it

plague - bacteria

List 2 diseases transmitted by lice and what kind of pathogen causes them

• typhus - bacteria

• louse-borne relapsing fever - bacteria

List 2 diseases transmitted by sandflies and what kind of pathogen causes them

• leishmaniasis - protozoa

• sand fly fever - virus

List 3 diseases transmitted by ticks and what kind of pathogen causes them

• crimean-congo haemorrhagic fever - virus

• lyme disease - bacteria

• relapsing fever - bacteria

Define an arbovirus

any group of RNA virus developed in arthropods 

List the 5 main steps of a mosquito life cycle

1. females lay eggs on raft in water, often in domestic areas

2. eggs hatch → larvae → pupa

3. eggs can be dormant indefinitely / larvae mature to adults in ~7 days

4. adults mate, females seek blood to nourish eggs

5. bites - Ades bite during the day, Anopheles bite at night

List the 3 main steps of transmission of arboviruses

• once a mosquito is infected, the pathogen spreads around the whole body via an open haemolymph circulatory system

• pathogen travels to salivary gland

• when the mosquito collects a blood meal, there’s an exchange of fluid, both blood into it and infected haemolymph into the host

Is zika mostly symptomatic?

no its mostly asymptomatic

List 5 symptoms of the zika virus

• fever

• rash

• headachs

• joint pain in 2-7 days

• microcephaly in infants

Define a PHEIC

an extraordinary event which is determined to constitute a public health risk to other countries

List 3 contributions to a fall in cases of the Zika pandemic

• infection conferred immunity

• ministry of health expanded mosquito control programs

• increased access to care and quicker identification and isolation of access prevented re-emergence

List the 4 steps in Dengue infection

• extrinsic incubation - virus infects the midgut of Aedes, eventually travelling to the salivary glands (8-10 days)

• human infection - one mosquito infects several humans

• intrinsic incubation - the onset of symptoms usually takes 4-7 days

• mosquito infection - mosquito takes a blood meal from a person with acute dengue

State 2 organisms that transmit dengue

• Aedes aegypti

• Aedes albopictus

How many serotypes of dengue are there?

4

List 4 factors to consider during ecological vector management

• where to treat

• resistance

• community engagemennt

• environmental risk

Aedes aegypti: location

lives near people and homes

Aedes aegypti: organismal preference

anthropophilic

Aedes aegypti: resistance

• 3% resistance to malthion

• 68% resistance to permethrin

• 27% resistance to deltamethrin

Aedes aegypti: eggs

lays multiple batches of eggs

Aedes aegypti: activity

crepuscular, occasionally nocturnal

Aedes albopictus: location

outdoors in more rural areas

Aedes albopictus: organismal preference

anthropophilic and zoophilic

Aedes albopictus: resistance

• 21% resistance to malathion

• 64% resistance to DDT

• 2% resistance to deltamethrin

Aedes albopictus: eggs

lays one egg batch per bloodmeal

Aedes albopictus: activity

crepuscular

Give an example of fungi being used for biocontrol against dengue

entomapathogenic fungi are non specific parasitic fungi that target mosquitos

Give an example of fish being used for biocontrol against dengue

Gambusia affinis are non specific and cause potential damage to ecosystems

Give an example of mosquito being used for biocontrol against denguee

larvae are voracious predators of other species of other mosquito larvae, including Ades aegypti

List 4 technologies for vector control

• SIT - sterile insect techniques

• IIT - incompatible insect techniques

• RIDL - release of insects carrying dominant lethal genes

• gene drives

Sterile insect technique: irradiation (5 steps)

1. mass rearing of insects takes place in special facilities

2. male and female insects are separated, ionising radiation is used to sterilise the male insects

3. male insects are released over towns or cities

4. sterile male mosquitos compete with wild males to mate with females

5. females mated with the sterile eggs lay infertile eggs, reducing the population

What is Wolbachia?

common entomopathogenic bacteria that reduces mosquitos ability to transmit viruses

How are incompatible insect techniques performed?

male mosquitos artificially infected with Wolbachia mate with females causing their eggs to die due to cytoplasmic incompatibility

How does Wolbachia cause eggs to die due to cytoplasmic incompatibility?

male gametes infected with Wolbachia have a different orientation of chromosomes during metaphase which is then unable to line up correctly with female gamete chromosomes

List 2 dominant lethal genes Oxitec has created in order to promote vector control

• OX513A 

• OX5034

What is the effect of the OX513A strain?

all offspring die

What is the effect of the OX5034 strain?

female offspring die, males pass on genes

How do the created oxitec gene strains cause mortality (2 points)

Tetracycline-repressible transcriptional activator (tTAV) controls yhe binding site of tetracycline operator (TetO) creating positive feedback loop, allowing downstream creation of the gene causing late larval lethality

• the introduction of tetracycline prevents mortality

How can the OX513A  be visually identified?

possesses a heritable fluorescent marker gene

How does CRISPR contribute to gene drives?

genetic modification alters gene drives to ensure phenotypic expression, in this case death of larvae

What pathogen causes Trypanosomiasis brucei?

protozoa kinoplastid

Where does Trypanosomiasis brucei operate?

extracellularly, inhibits blood plasma and bodily fluids

List 3 subspecies of Trypanosomiasis brucei

• T. b. brucie

• T. b. gambiense

• T. b. rhodesiense

What organisms do T. b. brucie target?

non human mammals

What organisms do T. b. gambiense and T. b. rhodesiense target and what does they cause?

humans, causing Human African Trypanosomiasis (HAT) - African sleeping sickness

What is the primary vector of Trypanosomiasis?

Tsetse flies

List 3 methods of diagnosis of Trypanosomiasis

• direct observation of parasite in peripheral blood, lymph, or CSF

• a CATT (card agglutination test for Trypanosomiasis) assay can be used for detection of T. b. gambiense antibodies, however there are high false positive rates

• LFIAs (lateral flow immunochromatographic assays) detect antibodies with high sensitivity and specificity

World Health Organisation - 2020

WHO eliminated gHAT as a global health problem

List 2 current targets of the WHO

• eliminating rHAT as a global health problem by 2030

• eliminate all transmission of gHAT

List 3 methods that WHO is using to eliminate transmission of HAT

• active screening

• passive screening

• vector control