Lecture 20- Conservation issues: Disease Flashcards
Why is understanding disease important?
-diseases affect population size and conservation
When was tasmanian devil facial tumour disease(DFTD) first discovered and when did it get bad and why?
- 1996
- sweeping epidemic by 2003
- by 2010 spread across 60% of Tas
- moving at about 7-20km/year
- 7-20 km is really fast in a mammal population
- carnivores= tend to move in larger areas
- the biology of the animal affects the spreading speed
What is tasmanian devil facial tumour?
- cancer cell line, transmitted by bites
- 100% mortality within 6 months of appearance of clinical lesions
- catastrophic decline of devil populations, a species that was widespread and of low conservation concern in the 1980s
- they bite each other when arguing over roadkills( food= very abundant)
How are they trying to save the Tasmanian devil?
-set up insurance populations= so they do not get infected
-breeding in captivity is difficult, need lot of space
-reservoir populations
=Hillsville
-tas devil= keystone predator so very important for the ecosystem
What are population dynamics?
- processes that make populations rise or decline
- these are mortality, fecundity and migration
- disease may impact these
What are the ways of detecting a disease? (6)
- Clinical evidence (when you can see the damage= unusual in the wild)
- Abnormal blood profiles
- Blood antibodies
- -ve population growth (population decline)
- Low fecundity
- High mortality
What should you try to find out about a disease? (7)
- Identify the cause= may be very difficult
- Impact on individuals
- Transmission (bite? air?)
- Prevalence
- Incidence
- Impact on population
- Disease distribution
What is the rubware disease?
- disease, of brushtail possums, where they lose some of their fur
- not high mortality, can impact on energetic requirements= as there is less fur especially in cold environments
- then it may impact survival or fecundity
What do transmission rates change with?
- with changing environmental conditions
- with population density and health (density of animals impacts the transmission rates
- higher densities= usually higher transmission rates
- also when higher density= less nutrition so may be more susceptible to disease)
What is prevalence?
-number of diseased animals in a population at the time if survey e.g. 40% infertile from disease
What is incidence?
- changes in the number of diseased animals in a population with time
- over several years or so
- high incidence causes population decline
What are causes of diseases? (6)
- Viruses
- Bacteria
- Parasites (protists, worms, arthropods)
- Fungi
- Nutritional (deficiencies, imbalances, toxins)
- Captive related diseases
What does endemic disease mean?
- in population for a long time
- usually more benign so it doesn’t lose all its hosts
What does epidemic disease mean?
- often recent and high impact
- population is naive
In what animals is the Pteropid or Australian Bat Lyssavirus found and what is it related to?
- related to classic rabies
- recorded in mega and micro bats
- more common in mega bats
- when it is in a group of bats, only some animals will suffer from it
What are the Australian Bat Lyssavirus (ABL) symptoms? (5)
- Initially enters muscle via bite usually
- Travels along nerves to CNS,and then nothing can save you once it is there
- Bizzare behaviour
- Meningitis= swelling of the brain
- Paralysis,convulsions and death
What is the treatment for Australian Bat Lyssavirus?
-standard rabies vaccine
How is Australian Bat Lyssavirus transmitted?
-bites
What is the impact of the Australian Bat Lyssavirus on bat populations?
- probably not huge
- but impact on humans so it is researched
What causes chlamydia in koalas?
- bacteria Chlamydophila/Chlamydia
- intracellular
- widespread in vertebrates
Where do koalas get chlamydia? (4)
- Eye- will scar and usually blind on one or both eyes, function normally with one eye(conjuctivitis)
- Urinary tract-then they will die
- Reproductive tract- won’t die but female reproductive system is damaged and are infertile
- Respiratory tract
How prevalent is chlamydia in koalas?
- 85-90% of adults exposed (surveyed for antibodies in blood)
- widespread: Qld to Victoria
- transmission: venereal in Vic
What is chlamydia like in males?
- if in reproductive tract then usually asymptomatic
What is the impact of chlamydia on koala populations?
- female fertility in infected population= 10-55%
- in uninfected population= 60-95%
- reduced fertility= lower population growth
- chlamydial infection alone is not a threat to the population
- in combination with climate change and increased mortality can wipe out populations
What is a parasite?
- dependent on host
- parasites environment is another organisms
- cause some harm
- may have multiple hosts in life cycle
What is Coccidia?
- parasite
- gut disease
- in orphaned marsupials
- common in feral cats that then infect others
What is Giardia?
- parasite
- in vertebrate intestine
- common in marsupials (Tas and Vic)
- transmission: contaminated water or food
- encysts
- get diarrhea and vomiting
What are the Cestoda?
-parasitic worms
-platyhelminthes
-cestoda
=intestinal parasites
=2 hosts in life cycle
=often benign
–but hypatid tapeworm: in kangaroos, they are the secondary hosts, originally from sheep, very bad, impacts the kangaroos
What are the Digenia (flukes)
- parasitic worms
- platyheminthes, digenia
- in liver, feed on blood, damage host tissue
- debilitating to animals as makes them more susceptible to predators etc.
What are the nematoda?
- parasitic worms
- occasionally damage host gut tissue but many species are benign
- they live in the gut, but do not attach to the wall of the gut
What arthropods cause diseases in animals? (3)
- ticks
- mites
- mosquitos
What disease do ticks cause?
- Ixodes holocyclus, tick
- causes paralysis in marsupials
- can be very bad for small animals if they have many ticks on= cause anaemia
What disease do mites cause?
-mange in wombats
What disease do mosquitos cause?
- act as vectors
- transmit Ross River Virus to marsupials and other mammals including humans
Are there seasonal patterns in parasite loads on koalas?
- yes
- seasonality in ticks
What are koala ticks like?
- seaonality
- 3 different life stages
- larval and nymph stages not on koalas, unclear what the intermediate host is
What is mange in wombats?
- cause by the mange mite
- loss of fur and eggs under skin, dry etc. these then split and get infected…death is likely if untreated
- can be treated
- differences in regional populations
- the distribution of wombats may be contracting if mange caused local extinction in small populations
What is an example of a fungal caused disease?
- Mucour amphibiorum
- platypus: abscesses (Tasmania), much more distributed than it used to be, , in 1995 only in one river system, now spreading
- frogs (Qld, NT, NSW): mortality
What is chytrid fungi responsible for?
- responsible for declines in some species of Australian frogs
- 1st discovered 1993
- infects skin,= keratinised tissue of adults
What are the clinical signs of chytrid fungus?
- sloughing skin, depressed, sluggish, no appetite, fail to display avoidance behaviour
- highly infectious
- causes mortality of adults including mass die offs in some frog species= population threat
What is the ecology of the chytrid fungus?
- distribution east coast + other sites
- spread mainly in water?
- greater impact in stream dwelling frogs
- greater impact at higher elevation
What are the key points? (3)
- Wildlife disease important to consider during research on wildlife and in particular impacts on population processes
- Also very important to think aboout quarantine between sites, to avoid moving disease agents between populations= responsibility of biologists
- Multidisciplinary studies is often the key in advancing our understanding of wildlife disease and their impacts on wild populations
