Infectious Diseases Week 5

What are the transmission sources for water-borne diseases

Potable water for consumption/cooking (undergoes extensive treatment including filtration and chlorination)

recreational water bodies (public ponds, lakes, swimming pools)

natural disasters (flooding can lead to water contamination with microorganisms)

How is the prevalence of water-borne diseases affected by climate change

increasing prevalence

Who monitors recreational/environmental waterways

The WA Department of Health

What is the Microbial Assessment Category (MAC)

Long-term bacterial water quality monitoring

What is the Sanitary Inspection Category (SIC)

Risk assessment of potential faecal contaminants

What organism causes giardiasis

Giardia duodenalis

What type of organism is Giardia duodenalis

An anaerobic protozoan flagellate

Where does Giardia infect

The small intestine, and occasionally the bile ducts

What is the cyst form of Giardia

Oval, thick-walled with four nuclei and several internal fibres.

Each cyst gives rise to two trophozoites during excystation in the intestinal tract

What is the trophozoite form of Giardia

Pear-shaped, with two nuclei, four pairs of flagella, and a suction disk

How is Giardia transmitted

By the oral-faecal route

What happens to trophozoites in the small intestine

They hatch in the small intestine (IECs) and are carried by peristalsis to the uninhabitable gut environment where they form cysts

Are Giardia cysts stable in the environment

Yes. Cysts are stable for long periods in the environment

What are the symptoms of giardiasis

Diarrhoeal, abdominal pain, flatulence, muscular weakness

What organism causes cholera

Vibrio cholerae

What type of organism is Vibrio cholerae

A Gram-negative bacterium, facultative anaerobe

Where does Vibrio cholerae live

In brackish or saltwater, attached to shellfish

Where is cholera endemic

In Africa, Southeast Asia, the Indian subcontinent, and Central/South America

What is the pathogenesis of cholera

Vibrio cholerae attaches to intestinal epithelial cells, grows, and releases toxins (cholera toxin and toxin-coregulated pilus). Diarrhoea can result in dehydration and death

How is cholera transmitted

By the oral-faecal route

What organism causes legionellosis

Legionella spp

What type of organism is Legionella

A Gram-negative bacterium, unculturable

Which species is the most common cause of legionellosis

L. pneumophila

How is Legionella transmitted

By inhalation of contaminated aerosols. Person-to-person transmission is rare

What is the clinical presentation of legionellosis

Acute pneumonia that can be fatal

What are the virulence factors of Legionella

Promote macrophage uptake;

Legionella-containing vacuole (LCV) modifies intracellular vesicles, cytoskeleton, inhibits secretory vesicles, disrupts mitochondrial function;

utilises host nutrient generation;

modifies host innate responses;

promotes cell exit from macrophage

What is the Legionella-containing vacuole (LCV)

A vacuole formed by Legionella within macrophages that modifies intracellular vesicles, the cytoskeleton, inhibits secretory vesicles, and disrupts mitochondrial function

What organism causes typhoid fever

Salmonella enterica serovar Typhimurium

What type of organism is Salmonella Typhimurium

A Gram-negative bacterium

How is typhoid fever transmitted

By the faecal-oral route

Are there known animal carriers of typhoid fever

No. There are no known animal carriers. Infected and asymptomatic human carriers exist

What do asymptomatic carriers of typhoid fever form

Biofilm on gallstones and epithelia

What does the capsular antigen of Salmonella do

It masks PAMPs to avoid neutrophil inflammation

What are the sources of food-borne diseases

Ingestion of foods containing preformed microbial toxins (does not have to grow in the host)

ingestion of pathogen-contaminated food (microorganisms can grow in the host)

Who is most affected by unsafe food

Infants, young children, the elderly, and the sick

How does climate change affect food safety

Climate change can increase food- and water-borne disease risks in many ways. Many pathogens are sensitive to changing temperatures, rainfall and extreme weather

What is the most common aetiological agent for foodborne outbreaks in WA

Salmonella

What other agents cause foodborne outbreaks in WA

Norovirus, Clostridium perfringens, Campylobacter, Hepatitis A, Vibrio parahaemolyticus, and unknown causes

What approach is required for disease outbreak investigation

A coordinated approach between various government agencies

What government agencies are involved in outbreak investigation

Local governments; Environmental Health Directorate, WA Department of Health; Population Health Units, WA Department of Health; OzFoodNet (WA); and Pathwest.

What are the three types of investigations required for an outbreak

1. Laboratory investigations (rapid detection methods require confirmation; molecular and immunology-based techniques),

2. Epidemiological investigations,

3. Environmental health investigations

What are the two types of swabs used in environmental testing

NRS II Transwab in Neutralising Rinse Solution and Environmental Flexi Swab (sponge swab)

What do these swabs test for

Aerobic Plate Count and/or E. coli Count; Listeria monocytogenes; Salmonella.

What type of organism is Staphylococcus aureus

A Gram-positive bacterium, spherical

Where does S. aureus grow

On common foods, skin, and the upper respiratory tract

What do some strains of S. aureus produce

Heat-stable enterotoxins

What species of Clostridium cause food-borne disease

C. perfringens and C. botulinum

What type of organisms are Clostridium spp.

Gram-positive bacilli

What do Clostridium spp. produce

Endospores that survive cooking and canning

Which Clostridium species is the most common cause of food-borne disease

C. perfringens

What is required to cause disease with C. perfringens

Ingestion of large numbers of bacteria

What does C. perfringens produce

A heat-stable enterotoxin

What are the effects of the C. perfringens α-toxin

It lyses blood and endothelial cells, increases vascular permeability, and causes hepatic toxicity and myocardial dysfunction

What are the effects of the C. perfringens β-toxin

It causes necrotic lesions

What is botulism

A severe, often fatal, food poisoning caused by an exotoxin

What are the gastrointestinal symptoms of botulism

Dry mouth, slurred speech, blurred vision

What are the neurological symptoms of botulism

Descending flaccid paralysis, respiratory failure, and death

What type of toxin causes botulism

A powerful, heat-labile neurotoxin

Does botulinum toxin cause flaccid or spastic paralysis

Flaccid paralysis (stops muscle contraction)

What is STEC

Shiga toxin-producing Escherichia coli

What are the main STEC serotypes reported in WA

O157:H7 and O128:H2

What does STEC produce and what does it cause

It produces verotoxin, leading to bloody diarrhoea and kidney failure

What complications can arise from STEC infection

Haemolytic-uremic syndrome and thrombotic thrombocytopenic purpura

What are other virulence factors of pathogenic E. coli

Heat-stable/labile enterotoxins, adhesins, adhesive fimbriae, and capsule

What disease does Listeria monocytogenes cause

Listeriosis

What are the clinical manifestations of listeriosis

May lead to bacteraemia and meningitis

What is a key growth characteristic of Listeria monocytogenes

Psychrotolerant growth at 4°C

What type of pathogen is Listeria monocytogenes

An intracellular pathogen that utilises host mechanisms

What is a zoonosis

An animal disease transmissible to humans

What role do wild animals play in zoonotic diseases

Wild animals are a reservoir for disease. They are not treated by vets or immunised the same way livestock or pets are

How are zoonotic diseases transmitted

Via direct contact, aerosols, or bites

What is an enzootic disease

A disease present endemically in certain animal populations (affects small numbers)

What is an epizootic disease

A disease with incidences reaching epidemic proportions in certain populations

How does rabies primarily occur

Primarily as an epizootic disease in animals

Can rabies spread to humans

Yes. It can spread as a zoonotic disease to humans, and also from wild animals to pets and infected pets to humans

What are the main reservoirs of rabies in the USA

Raccoons, skunks, mongoose, coyotes, foxes, and bats

How many people die from rabies annually

50,000+ people die annually, primarily in developing countries

How many people receive post-exposure prophylactic care each year

1 million+ people

Is there rabies in Australia

no

What type of virus causes rabies

Rabies virus – a negative-strand RNA virus (Rhabdovirus)

How does the rabies virus enter the body

Through a wound or bite

Where does the rabies virus proliferate

In the brain

What type of infection is rabies

A neurotropic virus that infects the CNS

How does the rabies virus spread within the nervous system

It enters peripheral neurons at axon termini and requires long-distance axonal transport and trans-synaptic spread between neurons for CNS infection

Is rabies lethal if not treated

Yes. Lethal if the individual is not vaccinated or given immediate care

What are the symptoms of rabies

Fever, excitation, pupil dilation, excessive salivation, anxiety, and fear of swallowing/water (hydrophobia)

What are the interventions for rabies control

Vaccination of wildlife (baits), rangers, and vets; monitoring of wildlife and numbers; education and risk management; diagnosis and treatment

How is rabies diagnosed in animals

Using tissue samples, particularly brain tissue, with tests such as the direct fluorescent antibody test

What assays monitor antibody responses in vaccinated animals

Viral neutralisation and enzyme-linked immunosorbent (ELISA) assays

Are there tests available to diagnose human infection immediately after suspected exposure

No. Currently no tests available that diagnose human infection with rabies immediately after suspected exposure

What is the treatment for suspected human exposure to rabies

The victim can be passively immunised with rabies immune globulin. A rabies virus vaccine also provides immunisation

How is rabies prevented

Largely through immunisation of domestic animals

How successful is the rabies treatment strategy in the US and Europe

Extremely successful – fewer than 3 cases/year reported in humans

What are arboviruses

Viruses transmitted by insect bites (e.g., mosquitoes, mites, ticks)

What type of genome do arboviruses have

Single-stranded RNA (ssRNA)

What does (+)-sense RNA mean

It has direct mRNA function – the host's ribosomes translate viral proteins immediately

What family do many arboviruses belong to

The family Flaviviridae

What are the five major diseases caused by Flaviviridae

West Nile fever (WNV), Yellow fever (YFV), Japanese encephalitis (JEV), Tick-borne encephalitis (TBEV), Dengue (DENV1-4)

What does dengue include clinically

Dengue fever, Dengue hemorrhagic fever (DHF), and Dengue Shock Syndrome (DSS)

What do some arboviruses cause

Encephalitis (inflammation of the brain)