lecture 11 HEALTH

what are conditions for disease emergence

- host

- agent

- appropriate environmental conditions

disease

any change in the normal function or structure of any part, organ, or system of a living body

Epidemiology

the study of disease in human or other animal populations

endemic disease (enzootic)

a disease that occurs with a predictable regularity and rate within a given population and area

epidemic disease (epizootic)

a disease that is occurring in a time or location where it does not normally occur or at a rate greater than historical norms

zoonosis

an infectious disease that can be naturally transmitted between humans and other animals

mortality

proportion of individuals in a population that die during a period of time

morbidity

proportion of individuals in a population that develop clinical disease

rinderpest

an acute infectious viral disease of cattle (usually fatal)

significance of rinderpest

poster child of a disease with wide ranging impact on wildlife, ecosystem, and human populations at a continental scale

introduction of rinderpest

introduced to Africa from Asia during colonization; spread from cattle to native ungulates

what type of virus is rinderpest?

Morbillivirus

weakness of rinderpest

- easy to treat with vaccinations

- can't exist outside of host for long periods of time, making isolation an effective treatment

when was rinderpest eliminated?

eliminated by the early 2000s (Asia: 2000, Africa: 2001, Last Global Detection: 2004)

chronic wasting disease (CWD)

Prion disease affecting deer and elk.

prion

a misfolded protein that causes disease

how is it spread of CWD

spread seems related to moving of captive infected animals; transmitted by contact with infected individuals or body fluids and tissues (mainly nervous tissue)

symptoms of CWD

weight loss over time, neurological and behavioral changes (ex. tooth grinding or loss of fear of humans)

what is the concern of CWD

rise in rates of geographic advancement

is there transfer of CWD to humans

never been a case of encephalopathy from CWD being transmitted to humans

encephalopathy

disease of the brain

real world implication of CWD

- big impact on hunting

- highlights weakness between public and private management of wildlife in the N.A. model

How does CWD highlight a weakness of the N.A. model of wildlife management?

origins of CWD traced back to domestic populations of elk;

interactions between wild ungulates and these domestic animals spread the disease.

Domestic individuals can be bought, but aren't able to be tested because they are privately owned

rabies

an acute viral infection that is most commonly transmitted to humans by the bite or saliva of an infected animal

significance of rabies

public fear and expectations are important stakeholder considerations with wildlife disease

rabies infecting humans

rabies is almost uniformly fatal in humans

vaccination for rabies

- vaccine works to prevent rabies, or has a roughly 1 week grace period to get the vaccine

- vaccines and bait technology used to cure wildlife

rabies from public health and wildlife perspectives

public health concerns limits official role of wildlife management agencies

African swine fever (ASF)

Highly contagious viral disease affecting pigs.

characteristics of ASF

- caused by Asfivirus

- 90 - 95% fatal to all swine

- highly infectious and persistent

- can be spread by flying scavengers (like flies) after consuming a carcass; can spread for multiple days

areas of concern for ASF

- hybrid populations of wild pigs and boar

- wild populations could infect domestic populations

white-nose syndrome (WNS)

a fungal infection that dehydrates hibernating bats, causing them to wake too early in search of water and food and they die

introduction of WNS

introduced from Europe, likely by humans from spelunking/caving equipment

treatment of WNS

infected bats treated with probiotic bacterium exhibit 5x higher survival rates than untreated bats

problems with treatment of WNS

each bat has to be treated individually (colonies can consist of thousands of bats)

implication of WNS on bat conservation

if WNS gets into a colony, we can see up to 90% declines

Brucellosis

bacterial disease which affects cattle

brucellosis in humans

- caused by contact with infected cows, or with unpasteurized milk

- treatable, creates a fever that comes and goes in waves

brucellosis in other animals

- found in elk and bison populations in late 19th century in Yellowstone NP

- transfer through mixed domestic and wild animal aggregations (ranchers leaving out food for cattle in winter also attracts elk and bison)

management of brucellosis

- culling elk herds (reduce density to reduce spread)

- govt. supplemental feeding to prevent mingling with domestic livestock

sociopolitical controversy

another point of controversy for farmers is the notable decline in outbreaks in correlation with wolf populations/predation

Rabbit Hemorrhagic Disease (RHD)

A calicivirus that causes a highly contagious, acute and often fatal disease

RHDV1

effects European rabbits; has been used as biocontrol for invasive rabbits (most notable in Australia)

RHDV2

discovered in France in 2010; effects many rabbit species, including N.A. native species (2020 outbreak in N.A.)

spread of RHDV2

extremely contagious for up to to months; spreads through carcasses or fluids

vaccination of RHDV2

vaccines being developed, but complications exist for using them in wild populations where disease is endemic

significance of RHD

rabbit decimation would severely disrupt trophic levels

canine distemper

viral disease of dogs, marked by fever and respiratory problems; caused by Morbillivirus

decline of canine distemper

declined immensely because of vaccination efforts started in the 1950s and continuing into the 1960s

persistence of canine distemper

once introduced to wildlife populations, it is difficult to get rid of

canine distemper in black-footed ferrets

- declared extinct, rediscovered in 1981

- 18 individuals captured for breeding programs

- highly sensitive to distemper and suffer high mortality

plague, prairie dogs, and black-footed ferrets

prairie dogs are the primary food source of black-footed ferrets; fleas on prairie dogs can carry the plague which leads to high mortality of the ferrets

vaccination for plague

- prairie dogs can be vaccinated through bait

- black-footed ferrets have to actually be injected

Bighorn Pneumonia

- bighorn populations have declined more than 90% on the Western U.S. and Canada

- much of this is attributed to diseases introduced by domestic sheep

treatment of bighorn pneumonia

- bighorns are difficult to vaccinate

- only current effective treatment is separation of bighorn from livestock (not practical)

Sea otter declines

- initial decline from fur harvest

- conservation concerns with Southern sea otters linked to pollution, harmful algae blooms, and diseases targeting prime age individuals (compromises individuals with strong immune systems)

significance of sea otter declines

sea otters primarily feed on sea urchins, which are harmful to kelp forest ecosystems; decline in sea otters lead to an increase in sea urchins and a decline in kelp forests

Relation between wildlife biologists and disease

often looked to for recommendations

cyclical nature of infectious agents

pathogens vary in lifecycle; infections can be seasonal

management through targeting control of specific agents

target organisms that spread diseases; Tsetse flies in Africa, Kissing bugs in U.S. to Mexico borderlands, Mosquitos

diseases caused by poisons/pollutants….

such as lead poisoning, can be mitigated or eliminated

host management

host behavior, spatial or temporal abundance, or other life history characteristics that can be managed influence epidemiology

examples of host management

- exclusion of avian species from infected areas

- exclusion of contact between domestic and bighorn sheep

- density reduction

Immunization

development and use of vaccines to boost immune systems of wildlife species; has been highly successful in the past (Rabies, canine distemper vaccines, rinderpest immunization)

issues with immunization

some disease organisms do not stimulate sufficient immune response for effective vaccination

environmental management

controlling environmental variables favorable to disease transmission

environmental management examples

- overgrazing of elk in California lead to spread of poison hemlock

- avian conjunctivitis

- animals translocation

- fire can restore natural/semi-natural distributional patterns for animals

One Health Initiative

concept that we need to seek and implement optimal solutions to health problems that maximize benefits to human health, animals health, environmental heath, and sustainability