parasitology lecture 7: a parasite's way of life pt. 3

what is vertical transmission?

The transmission of parasites from mother to offspring:

across the placenta, through breast milk (mammals), or

via infected gametes.

what is an example of vertical transmission?

Alaria americana - trematode's larvae can be transmitted

via breast milk.

◦ Recall life cycle has canid as a definitive host, snail as 1st

intermediate host, tadpole as 2nd intermediate host.

what is another example of vertical transmission? (transplacental example)

toxoplasma gondii

what is an example of transovarian transmission?

passing of Babesia

bigemina larvae from an infected female Rhipicephalus tick to her eggs

Rhipcephalus are one-host ticks.

◦ One-host ticks remain on the same host for the larval, nymph, and adult stages, only leaving the host prior to laying eggs.

◦ This limits their ability to transmit disease, except in the case of transovarian transmission.

Larvae already are infected when they hatch!

what is vector competence?

the ability of a particular

vector to acquire, maintain, and transmit a specific pathogen

Not all blood-feeding arthropods can serve as vectors. The parasite must...

◦ Survive the vector's digestive tract

◦ Penetrate the gut wall

◦ Reproduce and/or develop within the vector

◦ Migrate to appropriate location for transmission

(example = salivary glands).

◦ Achieve transmission when vector next feeds

what is vector capacity?

a measure of transmission potential

of a parasite from a vector population to a host

population.

◦ High vector capacity = a good vector for the parasite!

Primary vs secondary vectors

what are some factors that contribute to high vector capacity?

◦ Regular feeding on the host in question

◦ Feeding for an extended period and taking a relatively

large blood meal

◦ Abundance

◦ Good dispersal ability

◦ A life span long enough to allow the parasite to reach its

infective stage

what is the vector considered the deadliest animal?

mosquitoes

Only females blood feed and transmit disease.

what are the three examples of mosquitoe parasites and what diseases do they cause?

Anopheles - Malaria, Lymphatic filariasis

Culex - Lymphatic filariasis, West Nile

Aedes - Dengue, Yellow Fever, Zika

what is the life cycle of a mosquitoe?

eggs-> larvae-> pupae-> adults

what kinds of environments do the three mosquitoe types like to lay eggs in?

Anopheles - prefer marshy areas or near banks

for creeks/streams (eggs in water and they float).

Culex - lay eggs most environments (eggs in

water and they form "rafts").

Aedes - lay eggs in containers that hold water

(stick to sides).

what parasite does the tsetse fly transmit?

tyrpanosoma brucei (african sleeping sickness)

both males and females blood feed

what parasite does the sand fly transmit?

leishmania (leishmaniasis)

only females blood feed

what parasite does the black fly transmit?

Transmits Onchocerca (Nematode causing River Blindness)

and Leucocytozoon (malaria-like parasite of birds)

only females blood feed

what are kissing bugs?

These bugs are widespread in South and Central America and fair amount of North America.

About 155 species (most of which transmit Trypanosoma cruzi causing Chagas disease).

Both male and female

kissing bugs take blood meals.

Called Kissing bug because they like to feed at night on soft tissues (around lips and eyes)

parasite NOT passed in

saliva...but in the feces of bug!

what are fleas?

wingless insects and can jump far (up to 30 cm)!

Males and females take blood meals

Ectoparasite but can also

transmit some pathogens.

◦ Transmits causative agent of plague, murine typhus, and some tapeworms of veterinary importance.

Some parasites using the flea as a vector can block its glands and induces starvation.

◦ Once glands unblocked, starving fleas bite repeatedly, increasing transmission.

what are ticks?

Ticks are arachnids and both males and females blood feed.

Burrow into skin with mouthparts, may go unnoticed for days, but they feed continually.

Terrific vectors for many diseases:

◦ Lyme disease, RMSP, relapsing fever, tularemia, ehrlichiosis, red water

fever

QOTD: List 4 general modes of transmission

parasites utilize to infect their hosts.

vertical transmission, trophic transmission, fecal-oral transmission, sexual transmission