Disease Ecology Lecture Notes PDF

## Disease Ecology ### Today's Lecture - Brief introduction about me - What is disease ecology? - Some terms - hosts, pathogens, vectors - Emerging infectious diseases and their origins - Coronaviruses as a case study ### Associate Professor at University of Arkansas, USA Research on disease ecolo...

## Disease Ecology ### Today's Lecture - Brief introduction about me - What is disease ecology? - Some terms - hosts, pathogens, vectors - Emerging infectious diseases and their origins - Coronaviruses as a case study ### Associate Professor at University of Arkansas, USA Research on disease ecology - Pathogen discovery in wildlife in remote locations - Maintenance and transmission of zoonotic pathogens in wildlife ### Inherently Interdisciplinary Field Interactions among hosts, parasites, and the environment. - How parasites are maintained and transmitted in host populations. - Their effects on those individuals and populations. - Searching for reservoirs of zoonotic infections & tracing outbreak events. - Studying intervention effectiveness e.g., vaccination and culling campaigns. ### What is the environment? Environment = biotic and abiotic factors. - Host: Food resources, competitors, predators, climate etc. - Parasite: Mostly as above, plus the host immune system (analogous to predators). ### What is a host? - An organism in or on which a parasite lives. - Commensal relationship = one species lives on or in another without causing damage. - The term is situation dependent. Only a host while infected. ### Different hosts terms - **Reservoir vs intermediate vs amplification** - Reservoir = where the pathogen/parasite can be maintained indefinitely, Serves as a source pool for other species becoming infected. - **Tularemia in voles** - Serve as intermediate and amplification hosts. - **Bat reservoirs and intermediate hosts** - Hendra virus - Horses are intermediate and amplification hosts. - Sometimes intermediate hosts can lead to amplification. ### What is a parasite? - An organism that lives in or on (or very near) an organism of another species and benefits by deriving nutrients at the its expense. - What do we think of when we hear "parasite"? - Viruses - Bacteria - Helminths - Fungi - Protozoa - How is parasitism different to predation? ### What is a Pathogen? - **Pathogen** - a parasite that causes disease to its host. - **Disease** - a disorder of structure or function in a human, animal, or plant. - A pathogen is a parasite, but a parasite is not necessarily a pathogen - although many are. - Though these terms are often used interchangeably (in mainstream media etc.) - **Parasites and pathogens are transmitted between hosts. Diseases are not!** ### Emerging Infectious Diseases - An infectious disease that has either newly appeared in a population or been known for some time but is rapidly increasing in incidence and/or geographic range. - CDC: "Emerging infectious diseases" are defined as 'those whose incidence in humans has increased within the past two decades or threatens to increase in the near future. Emergence may be due to the spread of a new agent, to the recognition of an infection that has been present in the population but has gone undetected, or to the realization that an established disease has an infectious origin. Emergence may also be used to describe the reappearance (or re-emergence) of a known infection after a decline in incidence. ### Global Examples of Emerging and Re-Emerging Infectious Diseases | Category | Examples | |---|---| | Antimicrobial-resistant threats | CRE, MRSA, C. difficile, N. gonorrhoeae | | West Nile virus | West Nile Virus | | Cryptosporidiosis | Cryptosporidiosis | | Ebola virus disease | Ebola virus disease | | Diphtheria | Diphtheria | | MERS-CoV | MERS-CoV | | Enterovirus D68 | Enterovirus D68 | | Powassan | Powassan | | Heartland virus | Heartland virus | | E. coli O104:H4 | E. coli O104:H4 | | Drug-resistant malaria | Drug-resistant malaria | | Hepatitis C | Hepatitis C | | vCJD | vCJD | | Lyme disease | Lyme disease | | Lassa fever | Lassa fever | | HIV | HIV | | Akmeta virus | Akmeta virus | | Rift Valley fever | Rift Valley fever | | Typhoid fever | Typhoid fever | | SFTSV bunyavirus | SFTSV bunyavirus | | E. coli O157:H7 | E. coli O157:H7 | | H10N8 influenza | H10N8 influenza | | H7N9 influenza | H7N9 influenza | | H5N1 influenza | H5N1 influenza | | SARS | SARS | | Nipah virus | Nipah virus | | Hendra virus | Hendra virus | | Enterovirus 71 | Enterovirus 71 | | Human monkeypox | Human monkeypox | | Ebola virus disease | Ebola virus disease | | Zika virus | Zika virus | | H3N2v influenza | H3N2v influenza | | Cyclosporiasis | Cyclosporiasis | | Measles | Measles | | Human monkeypox | Human monkeypox | | Listeriosis | Listeriosis | | Bourbon virus | Bourbon virus | | 2009 H1N1 influenza | 2009 H1N1 influenza | | Adenovirus 14 | Adenovirus 14 | | Anthrax bioterrorism | Anthrax bioterrorism | | Chikungunya | Chikungunya | | Hantavirus pulmonary syndrome | Hantavirus pulmonary syndrome | | Dengue | Dengue | | Zika virus | Zika virus | | Human African trypanosomiasis | Human African trypanosomiasis | | Cholera | Cholera | | Hemorrhagic fever | Hemorrhagic fever | | Yellow fever | Yellow fever | | Marburg | Marburg | | MDR/XDR tuberculosis | MDR/XDR tuberculosis | | Plague | Plague | **Legend:** - Newly emerging - Re-emerging/resurging - "Deliberately emerging" ### Where do EIDs Come from? - **Zoonoses**: Diseases caused by pathogens transmitted from non-human animals, both wild and domestic, to humans. - **Re-emergence following control**: Multi-drug resistance (e.g., antibiotics)(e.g., Tuberculosis, MRSA), Vaccination failures (Measles, Polio) - **Evolution into new forms**: Influenza ### Sources of Emerging Infectious Diseases - Most EIDs are zoonotic; exceptions include antibiotic resistance and lack of vaccination compliance. - Most zoonotic EIDs come from wildlife. ### Cross-species Transmission as a Process | Stage | Transmission to Humans | |---|---| | Stage 5: Exclusive human agent | Only from humans | | Stage 4: Long outbreak | From animals or (many cycles) humans | | Stage 3: Limited outbreak | From animals or (few cycles) humans | | Stage 2: Primary infection | Only from animals | | Stage 1: Agent only in animals | None | | | Rabies | Ebola | Dengue | HIV-1 M | ### Factors driving spillover and disease emergence - Habitat loss/fragmentation - Human encroachment into wildlife habitats - Globalization **Table: Main categories of drivers associated with emergence and reemergence of human pathogens** | Rank | Driver | | ----- | ----- | | 1 | Changes in land use or agricultural practices | | 2 | Changes in human demographics and society | | 3 | Poor population health (e.g., HIV, malnutrition) | | 4 | Hospitals and medical procedures | | 5 | Pathogen evolution (e.g., antimicrobial drug resistance, increased virulence) | | 6 | Contamination of food sources or water supplies | | 7 | International travel | | 8 | Failure of public health programs | | 9 | International trade | | 10 | Climate change | **Ranked** by the number of pathogen species associated with them (most to least). **Cause human exposure to wildlife and their pathogens** ### Exposure, Spillover, and Emergence - **Exposure**: A point where there is potential for the pathogen to be transferred. - **Spillover**: The actual transmission of the pathogen to a new host. - **Emergence**: The establishment of the pathogen in the new host population. ### What happens to Ro during emergence? - "The basic reproduction number, RO, is defined as the expected number of secondary cases produced by a single (typical) infection in a completely susceptible population" - **Ro** is used to measure the transmission potential of a disease. - EIDs associated with increasing prevalence **Ro** must increase. - Mechanisms: - New pool of susceptible hosts (e.g., species jump -- ebola) - New pool of susceptible hosts (e.g., pathogen evolved -- influenza) - Change in infectious load in reservoir hosts (e.g., Nipah, Ebola, Hendra in bats) - **If Ro >1** the disease will spread indefinitely, **if Ro < 1** the disease will burn out (i.e., be removed). - Sometimes a short incubation period gives the appearance of a higher **Ro.** ### A case study - coronaviruses (CoVs) - Best known for SARS, MERS and now COVID-2019 - Diverse group of viruses hosted by mammals and birds - Spillover and host switches common ### CoVs in diverse wildlife - Four genetically distinct clades - Hundreds or thousands of CoV species in each clade - Alpha, beta, gamma and delta-CoVs - Alpha and Beta infect mammals (inc. humans) - Gamme and Delta infect birds - High CoV diversity in bats suggests ancestral host ### Seven known human CoVs (so far) - Human Coronavirus 229E - Human Coronavirus NL63 - Human Coronavirus HKU1 - SARS-CoV - SARS-CoV-2 - MERS-CoV - Human Coronavirus OC43 ### SARS - severe acute respiratory syndrome - The original SARS virus - Outbreak in 2003, 8098 infections, 774 deaths - Genetically very similar to SARS-CoV-2 - **Civet cats** likely intermediate host. ### MERS - middle east respiratory syndrome - Another CoV - 2574 confirmed cases, 886 deaths - More frequent spillover, less sustained outbreaks - Less efficient human-to-human transmission - From **camels** ### Studies on CoVs in bats up until 2014 - A big increase since then! ### Everyone is doing it... - More diversity of CoV in bats than any other animals - Usually this means they are ancestral host because of more time for divergence - Likely thousands of undiscovred CoVs - Very few likely pose risks to human health ### ...But we need bats - Pest suppression - Pollination - Seed dispersal ### One Health Philosophy - Human health is dependent on animal and environmental health. - Hence, to protect our health, we need to protect wildlife and their environments. - A tool for conservation and health prevention. ### Cross-disciplinary and collaborative approach This markdown summary describes the main points made in the given document. It utilizes headings and tables to organize the information clearly.