Vector-Borne Diseases: Chagas, Malaria & Drug Resistance

What is a vector-borne disease?

An illness transmitted by another living organism, usually a biting insect or other arthropod.

What is a disease vector?

A living organism that transmits a disease-causing agent between hosts.

What are the most common vectors of human diseases?

Mosquitoes.

Are diseases transmitted directly from host to host vector-borne?

No. Diseases like influenza spread directly between hosts rather than through vectors.

Can inanimate objects be disease vectors?

No. Vectors are living organisms.

What organisms can cause vector-borne diseases?

Viruses, bacteria, and eukaryotic parasites.

What determines the primary host of a disease-causing agent?

Where the disease-causing agent reproduces most.

Do all pathogens reproduce inside their vectors?

No. Some replicate inside vectors, while others do not.

What are arthropods?

Animals including insects and arachnids; they are among the most successful and diverse animal groups.

What percentage of identified animal species are arthropods?

Approximately 83%.

What are examples of vector-borne diseases and their vectors?

Malaria: Anopheles mosquitoes; leishmaniasis: sand flies; Chagas: kissing bugs; plague: fleas; West Nile: Culex mosquitoes.

What type of organism is a tick?

An arachnid.

Where do most vector-borne diseases occur?

Tropical and subtropical regions.

Why are vector-borne diseases uncommon in polar regions?

Temperatures are too cold for arthropods to survive year-round.

What is Chagas disease caused by?

A eukaryotic parasite called Trypanosoma cruzi.

What transmits Trypanosoma cruzi?

Triatomine bugs, also called kissing bugs.

How is Chagas disease transmitted by kissing bugs?

The bugs bite humans and defecate near the bite; infected waste can enter the body through an open wound or mucous membrane.

Why is Chagas disease difficult to identify?

Many infected people experience few or no noticeable symptoms for years.

How many Americans does the CDC estimate have Chagas disease, according to the notes?

Approximately 300,000, mostly people infected outside the United States.

What environmental change could expand the range of kissing bugs?

Warming temperatures and milder winters.

What causes malaria?

Eukaryotic parasites in the genus Plasmodium.

Which mosquito transmits malaria?

Female Anopheles mosquitoes.

Why do female mosquitoes bite humans?

They need blood meals to support egg production.

What are the two major Plasmodium species discussed in the notes?

Plasmodium vivax and Plasmodium falciparum.

Which malaria parasite is especially virulent in Africa and Asia?

Plasmodium falciparum.

Where was Plasmodium vivax historically widespread?

It was widespread historically and remains predominant in parts of South America.

What cells does the malaria parasite infect?

Liver cells and red blood cells.

What are common malaria symptoms?

Fatigue, pain, and high fever.

Why can malaria cause recurring symptoms?

Parasites can remain in the body and cause disease again later.

Who identified the cause of malaria in 1897?

Ronald Ross.

What is ethnobotany?

The study of traditional plant-based uses and treatments, including medicines derived from plants.

Where does quinine come from?

The bark of the Peruvian cinchona tree.

When was quinine isolated?

1820.

Why was quinine important historically?

It became an important treatment for malaria and was used by European colonizers in tropical regions.

Why does tonic water taste bitter?

Because it contains quinine.

What is artemisinin derived from?

A traditional Chinese medicinal plant.

Who isolated artemisinin's active compound?

Chinese scientist Tu Youyou in the 1970s.

What Nobel Prize did Tu Youyou receive?

The 2015 Nobel Prize in Physiology or Medicine.

What are examples of synthetic antimalarial drugs?

Chloroquine and mefloquine.

Why can doxycycline help prevent malaria?

It is an antibacterial drug that can interfere with the malaria parasite because the parasite has an organelle derived from bacteria.

What is prophylaxis?

Preventive treatment taken to reduce the chance of developing a disease.

Why can widespread use of one antimalarial drug become problematic?

It creates strong selection pressure favoring drug-resistant parasites.

What is a major example of antimalarial drug resistance?

Chloroquine resistance spread throughout malaria-endemic regions, and artemisinin resistance emerged in Southeast Asia.

Why are malaria vaccines important?

They can reduce childhood malaria infections and mortality.

What is an allele?

A version of a gene.

What does it mean when an allele is fixed in a population?

It is present in all members of that population.

What is antagonistic pleiotropy?

When one allele produces multiple effects, some beneficial and others harmful.

What is the Ester 1 allele example?

A mosquito allele that provides insecticide resistance but increases vulnerability to predators.

Why did Ester 1 spread along the French coast?

Selection for insecticide resistance was stronger than the opposing pressure from predation.

What is a trade-off in natural selection?

An advantage in one environment or trait may come with a disadvantage in another.

What is Ester 4?

An allele that provides less insecticide resistance than Ester 1 but has a smaller associated fitness cost.

What biological factors affect vector-borne disease transmission?

Vector breeding locations, insecticide resistance, host age and health, immunity, and parasite drug resistance.

How does climate affect mosquito populations?

Warm temperatures and increased rainfall can create favorable breeding conditions.

How can warmer temperatures increase mosquito reproduction?

They can shorten egg development and maturation times.

How can climate change expand vector habitats?

Longer summers and milder winters allow vectors to survive and reproduce in new regions.

How can increased precipitation encourage mosquito populations?

It creates more standing water where mosquitoes can lay eggs.

How can human migration affect vector-borne diseases?

People can carry pathogens into new locations where local vectors may transmit them.

How has malaria influenced human evolution?

It has created strong selection pressure favoring genetic variations that provide resistance.

What is positive selection?

Natural selection that increases the frequency of beneficial alleles in a population.

What is the Duffy antigen?

A protein found on the surface of red blood cells that Plasmodium vivax uses to enter cells.

How does Plasmodium vivax use the Duffy antigen?

It binds to the antigen to gain entry into red blood cells.

What does Duffy-null mean?

A person does not express the Duffy antigen on their red blood cells.

How does being Duffy-null affect malaria susceptibility?

It makes infection by Plasmodium vivax more difficult.

What type of mutation can produce the Duffy-null condition?

A mutation affecting the promoter region of the gene encoding the Duffy antigen.

Why is the Duffy-null allele common in some African populations?

Historical malaria selection favored individuals who lacked the antigen.

What is thalassemia?

An inherited blood disorder caused by mutations in genes involved in hemoglobin production.

What are possible symptoms of thalassemia?

Fatigue, bone problems, enlarged spleen, jaundice, dark urine, and slowed growth.

What is heterozygote advantage?

When individuals with two different alleles have greater fitness than either type of homozygote.

How can thalassemia provide malaria resistance?

People carrying one thalassemia allele can gain protection against malaria without experiencing severe anemia.

Why can thalassemia alleles remain common in malaria-endemic regions?

Heterozygote advantage maintains them through natural selection.

What is G6PD deficiency?

An inherited deficiency of glucose-6-phosphate dehydrogenase, an enzyme involved in red blood cell metabolism.

Where is the G6PD gene located?

On the X chromosome.

Why is G6PD deficiency more common in males?

Males generally have only one X chromosome, so one recessive disease allele can produce the condition.

How does G6PD deficiency help protect against malaria?

Plasmodium falciparum grows more slowly in red blood cells expressing the enzyme deficiency.

How many people worldwide have G6PD deficiency, according to the notes?

Approximately 400 million.

What can trigger hemolytic anemia in people with G6PD deficiency?

Certain foods or medications that cause oxidative stress in red blood cells.

What is hemolytic anemia?

A condition in which red blood cells are destroyed faster than they can be replaced.

What is favism?

A reaction to fava beans in people with G6PD deficiency.

Why can some antimalarial medications cause problems for people with G6PD deficiency?

They can trigger the destruction of red blood cells.

What does malaria-related genetic variation demonstrate?

Infectious diseases can drive recent positive selection in human populations.

What is a haplotype analysis?

A statistical method used to study patterns of linked genetic variations and estimate their evolutionary history.

What do different malaria-resistance alleles in different regions suggest?

Malaria created geographically specific evolutionary selection pressures.

What type of virus is West Nile virus?

A positive-sense, single-stranded RNA virus.

Which mosquitoes transmit West Nile virus?

Culex and Aedes mosquitoes.

What is the primary host of West Nile virus?

Birds.

Why are humans considered incidental hosts of West Nile virus?

Humans can become infected and sick, but generally cannot transmit enough virus back to mosquitoes.

What is a dead-end host?

A host that becomes infected but does not transmit enough pathogen to continue the transmission cycle.

What animals are important West Nile virus hosts?

Birds such as American crows, robins, house finches, and house sparrows.

Which animals can become sick from West Nile virus besides humans?

Horses.

When was West Nile virus first introduced into the United States?

1999.

Where were the first recognized US cases detected?

Among exotic birds at the Bronx Zoo in New York City.

How was the US West Nile virus introduction traced?

Phylogenetic comparisons showed the virus was most similar to a strain from Israel.

What is phylogenetics?

The study of evolutionary relationships using genetic information.

How can drought increase West Nile virus transmission?

Birds congregate around fewer water sources, increasing contact and transmission.

How can warmer temperatures increase West Nile virus transmission?

They can speed mosquito development and reproduction and increase the number of infected mosquitoes.

What is dengue caused by?

A positive-sense, single-stranded RNA virus.

Which mosquitoes transmit dengue?

Aedes aegypti and Aedes albopictus.

How many major dengue virus strains exist?

Four: dengue 1, 2, 3, and 4.

Can antibodies against one dengue strain fully protect against another?

No. Antibodies from one strain do not necessarily protect against the others.

What is severe dengue sometimes called?

Bone-break fever.