Global Health Midterm

Factors associated with human population growth through history and pandemics

Increase in fertilizer oil and gas electricity

Infectious Diseases

generally transmitted from person to person, or by a vector.

Chronic diseases

develop in populations related to environmental factors and lifestyles. (diet, physical activity, exposures to hazards)

Communicable Diseases

an illness caused by a pathogen typically a virus or bacteria that can spread from one person or animal to another.

Infectious Disease

disorders caused by organisms such as bacteria, viruses, or fungi.

6 major types of pathogens

prions, viruses, rickettsia, bacteria, protozoa, and helminths

Epidemic

outbreak and spread of an infectious disease that affects a large number of people within a community, country, or region.

pandemic

an outbreak occurring over a very wide area, crossing international boundaries and usually affecting a large number of people.

outbreak

the sudden start of a disease

social and environmental factors associated with pandemics

• Population growth

• Urbanization

• Crowding

• International travel

• International trade

• Poor sanitation/Hygiene

• Environmental degradation/contact with wild animals

Pandemic Frequency

New pandemics occur on average every 40-50 years.

the combined duration of pandemics is approximately 400 years

Prevalence

the number of disease cases occurring at a particular time stated as a fraction

Incidence

the number of new cases over a particular time stated as a fraction (usually per thousand of population)

SIR

In a population, disease transmission depends on the number of Susceptibles, Infected, and Recovered

3 pandemics prior to the 21st century

Influenza, Cholera and the Plague

Case-fatality rate

the proportion of people diagnosed with a certain disease, who end up dying of it.

Well - known infectious diseases

Ebola, 1918 flue, SARS, COVID, Seasonal flu, swine flu

Spatial epidemiology

maps that provide an insight into the origins, spread and potential causes of infectious diseases.

Additionally allow people to understand the effects of different public health policies and actions on spread (prevention).

Also allow us to visualize biological factors that may govern spread in population

Spatial aspects of disease spread

as waves

via diffusion

along corridors

between hubs

via long-distance dispersal

evidence for past epidemics/ pandemics prior to the 20th century

written records

paleo-pathological evidence

clinical case

routine infectious disease epidemiology relies on reports of notifiable diseases.

when is a “case” a case

the patient should experience symptoms from the infection and be ill enough to seek medical care or advice.

the physician then has to make a preliminary diagnosis; and send a sample to the laboratory.

Latency and infection

a state of infection where an infectious agent is present in the body but is not causing symptoms

R0

The reproduction number of a disease

when R0 is less than one, this means that on average, each infection will result in less than one additional infection. in other words, the disease will die out.

R0 importance in epidemiology

important metric for understanding the transmissibility or contagiousness of viruses

Index case

the first identified case in a group of related cases of a particular communicable or heritable disease.

Notifiable disease

a disease that is legally required to be reported to government authorities

herd immunity

a point at which a disease has difficulty spreading through a population because a sufficient percentage of people are immune to it.

Zoonoses

Some animal species can act as reservoir hosts that harbor pathogens.

Contact between humans and wild animals may foster an exchange from a reservoir host to a human.

Immunologically naive

Having an immune system that has never been exposed to a specific antigen.

Spillover

the events that involve transmission of a pathogen from one species to another.

Spillover examples

the flu, HIV, COVID

Ebola and non-human primates

apes and monkeys, can be infected with Ebola, but they are not considered natural hosts

Ebola in Africa social/ environmental factors that explain why its so deadly

poor healthcare infrastructure, inadequate public health systems, mistrust in medical practices, traditional burial rituals, and environmental factors including deforestation

Five zoonotic diseases

Malaria

Measles

Smallpox

Tuberculosis

Plague

Vector-borne diseases

illnesses caused by parasites, viruses, or bacteria that are transmitted to humans by blood-feeding arthropods, such as mosquitoes, ticks, and fleas

Zoonotic diseases

Infections that are spread between humans and animals

Epizootic cycle

the process of an epidemic in animals, which is divided into four phases: enzootic, preepizootic, epizootic, and postepizootic

Enzootic cycle

the natural transmission of a virus or disease between wild animals and insect vectors

habitat fragmentation

the process of breaking up a large habitat into smaller, isolated pieces

may facilitate a higher disease risk

How do we determine intermediate/ resorvoir hosts?

use spatial epidemiology to investigate the wild animal populations near the source of outbreak

search for pathogen DNA/RNA in potential animal hosts

Sequence the pathogen DNA/RNA in potential animal hosts

Determine if a host is positive, determine the degree of similarity between pathogen DNA in hosts and that of the pathogen itself

Pangolins, bats, and COVID

Researchers have found that SARS-CoV-2 in humans shares about 90.3% of its genome sequence with a coronavirus found in pangolins. 

pangolin meat is a delicacy in China and Vietnam

wet markets

dedicated, completely or partially, to the sale of meat, fish, produce and other perishable goods. 

Hantavirus in the US

known as “New World” hantaviruses and may cause hantavirus pulmonary syndrome (HPS).

Hantavirus disease surveillance in the United States began in 1993 during an outbreak of severe respiratory illness in the Four Corners region – the area where Arizona, Colorado, New Mexico, and Utah meet

Hantavirus and climate change

Disease emergence is directly linked with the climate. rodents are the natural reservoir of the agent of HPS

Characteristics of microparasites

small relative to their hosts, reproduce at high concentrations within or upon the bodies of their hosts, and generally confer long-lasting immunity in the host after recovery from infection.

Characteristics of macroparasites

larger, usually do not multiply in their hosts but produce transmission stages; their tendency to induce immunity depends on the intensity of infection and is usually transient.

different types of parasite transmission

Horizontal (direct), Vector-borne, sexual, vertical, cadavers, persistent infective stages, waterborne, trophic transmission, environmental.

Van Leeuwenhoek

first observed protozoa and bacteria using a hand-made microscope in 1675.

discovery and first visual obervation of viruses

in 1898 when Dmitri Ivanovsky used special filters to isolate the tobacco mosaic virus

viruses were not observed until the advent of the electron microscope in the 1950s.

Prion diseases

infected brain turns into a sponge. “spongiform encephalpaties”; leaves the brain riddled with holes. this includes Creutzfeldt-jakob disease, kuru, fatal familial insomnia, and Gerstmann-straussler-scheinker syndrome.

How do viruses work?

Once it gets into a host's body, it travels along the surfaces of cells until its proteins begin to bind with receptors on the cells. The virus and the cells then fuse, allowing the DNA or RNA inside the virus to enter the cells, where it begins to reproduce.

Three ways of prion infection

ingestion of prion-containing food

prions are resistant to disinfectants like UV, high temperatures through cooking

mutant prions may be inherited

Mad Cow disease

a fatal brain disease in cattle that is caused by a prion.

RNA viruses

Replicate in two ways:

RNA-dependent RNA synthesis (the majority which includes measles, influenza, polio, etc)

by RNA-dependent DNA synthesis, so called reverse transcription followed by DNA replication and transcription.

Antigens/ Immunogens

the proteins in viruses and bacteria that trigger an immune response.

they have to discriminate between foreign antigens such as viral proteins, that are non-self and those antigens that are seld, one’s own proteins.

our survival depends on this system.

DNA viruses

A group of viruses that are linked to many infectious diseases and can cause fatal disease, especially in children and immunocompromised patients

Viremia

the term used to indicate that an infective virus is present in the blood stream.

Innate immune response

immediate and already present

involces INFs (inteferons and other cytokines)

natural killer cells

Antigen-presenting cells

Adaptive immune response

Antigen specific and acquired

T cells and B cells that have learned to recognize antigens

specific antibodies, some of which remain permanently to fight reinfection.

Prokaryotes

a simple structure lacking a nucleus and membrane-bound organelles, containing a cell wall, plasma membrane, cytoplasm, a single circular DNA molecule located in a region called the nucleoid, and ribosomes

its primary function is to carry out basic life processes like metabolism

Eukaryotes

has a plasma membrane, cytoplasm, and ribosomes

primary function is to carry out complex cellular processes like protein synthesis, and energy production.

Gram Negative

resistant to antibiotics

stain red when gram staining is used on them

Gram Positive

give a positive result in the gram staining test, puts the bacteria into a category based on their cell wall.

How do bacteria cause disease

Bacteria can be invasive (spread through tissues, usually using digestive enzymes which damage tissues and kill cells)

Bacteria can be toxigenic (produce toxins)

Host processes (host defenses like inflammation may over-respnd and cause significant tissue damage)

Five diseases caused by bacteria

cholera

staph infection

meningitis

Pneumonia

tuberculosis

TB as a major infectious disease

TB is highly deadly, affecting all age groups

leading in the worlds deaths from an infectious agent

in 2018, 1.7 billion people were infected by TB bacteria

claims 1.5 million lives per year

How is TB spread

Spread through the air from one person to another.

when a person breaths in the TB bacteria, it can stay in the lungs and begin to grow.

TB and COVID

COVID and TB have similar symptoms, which can lead to a misdiagnosis with TB

wearing a mask and staying six feet away can help with TB

How is Influenza transmitted

through respiratory droplets and contact with contaminated surfaces.

Flu Pandemics in the 20th century

1918-19 flu

the second wave in fall 1918 of Influenza was the most deadly (near the end of the war)

the virus had mutated into a deadly form over the summer of 1918.

it affected healthy young people

first major outbreak was in military camps

Spanish Flu (why was it so deadly)

the virus became bad quickly, first presenting normal flu like symptoms, then the virus would multiply in the lungs causing fluid build up.

socioeconomic factors, global war weakened some populations, public resources were small, supressed information about outbreaks, poor populations.

H5N1

The swine flu

2009

between 43 - 89 million cases

found recently in cows

AMR

Anti-microbial resistance

leading cause of death worldwide

where is AMR most prevalent and why

low and middle income countries, because of poverty and inequality.

AMR deaths

fluoroquinolones and beta-lactam antibiotics accounted for an estimated 70% of deaths

Antibiotic use globally

south america, africa and asia have the highest change in antibiotic doses.

which diseases are responsible for high AMR deaths in humans

Staphylococcus, E. coli, K. Pneumoniae

Helminth diseases

about ¼ of the wprlds population is at risk

the five diseases caused by Helminths are Pinworm, roundworm, beef tapeworm, pork tapeworm, and schistosomiasis

Factors that are associated with transmission of helminths in humans

low socioeconomic factors, poor sanitation, no access to clean water, poor hygeine, etc.

where are helminth diseases most prevalent

rural areas

sub tropical/ tropical regions

NTDs (Neglected tropical diseases)

Leishmaniasis

rabies

dengue

leprosy

DALYs

a measure of morbidity known as Disability adjusted life years = YLD + YLL

diseases that produce the most DALYs

Flu, TB, HIV/AIDS and invasive pneumococcal diseases.

Where are DALYs high globally

Africa

Protozoans

microscopic one - celled organisms that can be free-living or parasitic in nature.

they can multiply in humans

protozoans can transmit is differing ways depending on where they are living in humans.

Protozoan diseases

Malaria (vector born)

Leishmaniasis (vector born)

Cryptosporidiosis (water/food born)

Amoebiasis (water/food born)

Cryptosporidiosis

symptoms include: diarrhea, dehydration, fever and weight loss

transmitted via recreational water, undercooked food, touching contaminated hands, exposure to human or animal fecal matter.

has a high tolerance for chlorine

Leishmaniasis

transmission cycle of this parasite may involve infected animals, such as rodents or dogs, along with sand flies.

CL vs VL leishmaniasis

both prevalent in south america, africa, and parts of asia

CL is the most common form

VL is the most severe form

Initial and later responses to Covid

Initial:

closing border, stopping air travel, repatriating citizens, local and state level lockdowns, and mobilization of resources

Later:

gloves, masks, gowns, etc, test kits to hospitals and pharmicies, enhanced shutdowns and lockdowns (particularly in europe and asia), acceleration of vaccine development and rollouts.

Why flatten the curve

to ensure that cases have protective measures, and lower the daily number of cases.

three countries where covid was most problematic in the early days

India, US, Brazil

Race and Age and COVID

Non-hispanic AMerican Indian, and Black people were the most affeced

people over the age of 85 were most affected

why the world failed to contain covid

deficiency in the global alert system and the fragility of the International Health Regulations (IHR-2005), (2) problems of the international response to the pandemic, related to global health governance,

Co-morbidity and why its important in clinical outcome

medical conditions that you have in addition to a primary diagnosis.

Force of Infection

the rate at which a susceptible person in a population becomes infected with an infectious disease

Zika as an Emerging Infectious Disease (EID)

transmitted to humans through the bite of infected Aedes species mosquitos

fever, rash, joint pain, red qyes, ususally pretty mild

can cause microcephaly for babies from pregnant mothers

Gullian-Barre: temporary paralysis for some patients

Zika in 2016 Miami

WHO declared Zika a global health emergency in 2016

there is currently no Zika transmission in the US.

Aedes Aegypti basic ecology

can be found in tropical and subtropical regions

highly adapted to live near humans and their habitats