5 - Important Zoonotic Diseases Flashcards
WHO’s definition of a zoonosis
an infectious disease that has jumped from a non-human animal to humans. The pathogen may be bacterial, viral or parasitic, or may involve unconventional agents and can spread to humans through direct contact or through food, water or the environment.
How many organisms are known to be pathogenic to humans? How many are zoonotic? Emerging?
1415 known
868 (61%) zoonotic
175 emerging
Stages of a zoonosis
Stage 1: agent only in animals
Stage 2: primary infection
Stage 3: limited outbreak
Stage 4: long outbreak
Stage 5: exclusive human agent
Slide 4** examples
Examples of important human diseases that no longer require animal reservoirs
- measles (Cattle)
- dengue (Monkeys)
- malaria (Gorillas)
- HIV (Chimps)
HIV-1 origin story
Comes from cross species transmission of related Simian Immunodeficiency viruses (SIVs) which are nonpathogenic in their natural hosts (chimps)
Transmission likely through bushmeat hunting
Lineages of HIV and which is most important
Groups M, N, O, P
HIV-M from SIVcpz in SE Cameroon: worldwide spread
HIV-M origin story
Emerged in Kinshasa
Infected blood/tissue of the residents dated back to 1959
Connects to SE Cameroon by river; likely went downriver
Yellow fever origin, reservoir and how it got to the new world
Africa, Monkeys
Slave trade caused dissemination of its primary vector, Aedes aegypti, into the new world
Describe yellow fever in the USA
150 000 people died
New York (1668), Boston (1691), Philly (1793)
How did Yellow fever impact the first world war?
Critical role in haitian independence, 2/3 mortality among 40,000 Napolean’s army
What is interesting about yellow fever in Brazil?
Not a typical urban outbreak (not Ae aegypti vectored): was in non-human primates and spilt over into humans living at edge of forest
Types of influenza, their differences
A: most severe human infection, is the type that is zoonotic
B and C: restricted to humans
How does influenza undergo genetic change?
Mutation and gene reassortment affecting the ability to attach to mucosa of specific species
The rapid genetic change in influenza results in…
- antigenic drift (minor genetic change)
- and antigenic shift (emergence of a very different virus)
How do birds affect influenza
Shorebirds are a key reservoir for influenza viruses
Migration flyways pass through densely populated human areas
They stopover and defecate, infect ducts/other waterfowl, which affect mammals which affect humans
Slide 15
Different cases of pandemic influenza
- H1N1 Spanish influenza in 1918 (direct from avian host)
- H1N1 Swine influenza in 2009 (viral reassortment in pigs)
MERS CoV stands for… Its host? Mortality? Outbreak?
Middle Eastern Respiratory Syndrome Coronavirus
Dromedary camels primary animal host
Outbreak in Saudi Arabia in 2012
35% mortality
Transmission of SARS-CoV-2
Can be infectious before symptoms are present
By air: large droplets 1-2meters
Fomites: contaminated inanimate objects?
Two steps in new SARS-CoV-2 variants
1: Mutation (highly mutable RNA virus)
2: Natural selection, mainly in favour of spike proteins that are more transmissible (more infectious virus outcompetes earlier strain)
Why is there potential for emergence of new coronaviruses from animals?
- 9% of bats from Asia, Africa, Latin America carry at least one coronavirus
- genetic recombination
Effects of West Nile Virus on humans
80% asymptomatic
20% West Nile Fever
<1% neuroinvasive disease
Vector and host of WNV. Describe them
Mosquito vector
Birds are amplifying hosts (jays, crows; minimal clinical infectious, high viremia)
Many vertebrates (including humans) are dead end hosts (low viremia; do not infect mosquitoes)
Where did WNV emerge? In the western hemisphere?
Uganda 1937
WH 1999 (NYC) through migratory birds and mosquitoes
Describe WNV in New York
Human encephalitis outbreak
High number of dead crows
Exotic birds at Bronx zoo developed encephalitis, vets identified WNV
Future spread of WNV in Canada
With increases temperatures, it is now found in Canada and likely to increase
Has been found in Quebec, Ontario most prominently
Describe Q fever (agent? reservoir? transmission?)
Coxiella burnetii (coccobacillus)
Zoonosis with main reservoirs: cattle, sheep, goats
Aerosol transmission (sheep placenta); travels distances, remains suspended in the air
Where is Q fever found
Worldwide (except Antarctica, Arctic, NZ)
Describe the Q fever outbreak in the Netherlands
2007-2012
Largest outbreak
4,000 confirmed, 40,000 estimated human cases
Abortion storms started in 2005
75X increase in goat populations leading up to outbreak
Living within 2km of dairy goat farm = infected
How does wind affect Q fever
Wind patterns/speed/direction affect who is infected
Areas around Marseille have high prevalence bc winds blow over rural areas/farmland
Slide 40-42
Just read
Most human cases are caused by what kind of Brucellosis? What kind of agent? The reservoir is…
B melitensis
Bacteria
Reservoir is goat, SHEEP, cattle, camel, buffalo
Where is Brucellosis emerging
China
Increased livestock over time period to meet meat demand
Spatial relationship between livestock and cases
How is Brucella an animal husbandry issue?
Abortion
Risk of animal products given to humans (humans infected through consumption of unpasteurized dairy products)
How does Brucella affect human health
High morbidity: fever, weakness, sweats, weight loss, infection of liver/spleen, bone, joint
Can last days to months
Diagnosis difficult
Antibiotic treatment effective
Transmission of Brucellosis
- unpasteurized dairy products
- undercooked meats
- infected animal secretions entering wounds, eyes, aerosolization
- lab work
Human-human transmission of brucellosis
Extremely rare but: vertical, breastfeeding, sexual, blood transfusion
How to prevent brucellosis
Address the reservoir (cull infected)
Abattoir/slaughterhouse safety education (ventilation)
Immunization (animal vaccine prohibited in Canada)
Downstream measures: pasteurize milk products
Parasites of interest
- Trichinosis
- Leptospirosis
- Fasciola
- Babesiosis
- Toxoplasmosis
Parasite, reservoir, human symptoms and treatment for trichinosis
Helminth that invades muscle and other tissue following ingestion of infected, uncooked meat
Reservoirs: pigs, bears, other mammals
Symptoms: severe muscle pain and fever, fatality
Treatment: supportive (adult and immature worms do not survive very long)
Prevention of trichinosis
Avoid feeding of potentially infected meat to pigs
Inspection of meat
Adequate cooking or freezing of meat, especially pork or bear
Causative agent, illness, reservoir of Leptospirosis
Leptospira (spirochete)
Febrile illness
Reservoir: rodents, dogs, cattle
Transmission of Leptospirosis
cutaneous exposure (cuts/breaks in skin) to contaminated fresh water, damp soil
Why is Leptospirosis an issue
- non-specific clinical illness
- diagnosis difficult
- ubiquitous in warm parts of the world
Describe Fasciola in animals
Significant disease in sheep, cattle
Causes physical wasting, sheep liver rot
Describe fasciola in humans
Fever, abdominal pain
Difficult diagnosis (from stool)
Prevention of Fasciola
Control in domestic animals: snail, de-worming of grazing animals, animal vaccine in development
Avoidance of uncooked water plants in endemic areas
Why is Fasciola resurging
Due to overwintering of infected snails with climate change
Distinctive issues of fasciola
- health problem for herd animals
- human health concern
- foodborne via plant consumption
Babesiosis is caused by… Transmitted through? Reservoirs?
Babesia microti (protozoan red blood cell parasite)
Transmitted by Ixodid tick (like Lyme disease)
Deer, bovine, rodent reservoirs
Babesia is the #1 what-related disease in the US?
Transfusion
Prevention of babesia
Tick avoidance and repellant
Agent of Toxoplasmosis. Clinical effect in humans
Toxoplasma gondii (protozoan parasite)
Mostly asymptomatic (latency*). Can reactivate in immune suppressed
Congenital syndrome if acute infection in pregnancy
Rarely, eye disease
Toxoplasma hosts and transmission
Felids are definitive hosts, food animals are intermediate hosts
Transmission through consumption of uncooked meats, contact with cat feces, mother to child
Toxoplasma prevention
Cook meat
Careful handling cat feces
Screening/treatment of pregnancy women
Toxoplasmosis issues
- latency
- congenital infections
- pet related
- food borne
What agent causes Chagas disease? It is an…
Trypanosoma cruzi
Immigrant disease (traditionally seen in rural poor)
Clinical effects of chagas disease
Most asymptomatic
Symptomatic = fatal gastrointestinal or cardiac disease after many years of infection
Vector of chagas disease, describe it
Reduvid bug (kissing bug)
Bite domestic, peridomestic and wild animals
Live in mud walled, thatch roofed huts
Bite at night, transmission if from infected bug FECES
Characteristics of the reduvid bug that favour control
- highly susceptible to insecticides
- low reproductive rate
- low genetic variability
Other routes of transmission of chagas disease
Transfusion
Perinatal transmission (mother to child)
Oral transmission (crushed bug ingested)
Issues with chagas disease
- multiple routes of transmission
- long latent period
- wild/domestic animal reservoirs
- poor treatment
