Week 11 - Infectious agents as a cause of subclinical disease in animals Flashcards
What are subclinical disease in animals
Diseases that are hard to detect in animals
What is one way to cause subclinical disease to turn to clinical
Due to other factors which often are environment that shift in favour of pathogen
- Weather
- Dietary change
What are some individual sub-clinical disease
- Dog with early stage of heartworm infection
- Cat with calicivirus
- Sheep with low nematode burden
- Cow with sub-clinical mastitis
- Parainfluenza virus in cattle without any associated bacterial disease (feedlot example)
- If sub-clinical disease remains sub-clinical at the individual level it may never result in problems (when did you last take an anthelmintic?)
What are some group sub-clinical disease
- Sheep nematodes
- Sheep lice
- Cattle nematodes
- Cattle mastitis
- Feedlot pneumonia (shipping fever)
- Johne’s disease (ruminants)
- Roundworms in puppies
- Cattery with calicivirus
- Pound with parainfluenza virus
What are the Clinical signs of mastitis
- Change in colour of milk
- Change in consistency of milk
- Change in volume of milk produced
- Animal may stop eating
- Change in size of udder
- Change in udder “tone”
What may be the direct loss of costs
– Reduced milk volume
– Reduced milk quality & changed payment band
– Reduced market access, poor quality milk may not be suitable for some applications eg. cheese
What may be the indirect loss of costs
– Reduced condition score
– Reduced reproductive success
– Increased chance of culling (cost of replacement)
– Infection of other stock
What maintains the infection in a farm
- Sub-clinical disease can be a vital method for pathogens to remain on a property
- Very difficult (if not impossible) to eradicate many nematode parasites from grazing properties
- Eg. Nematode population = animal + environment
- Different selection pressures on two different populations
How can weather lead to the change of sub-clinical disease for foot abscess
– Disease of sheep caused by multiple bacteria – Requires damage to hoof – Usually in wet conditions – Usually heavy sheep – Particularly after yarding them – Leads to abscess in foot (hence name!)
What can drought affect in the fields
– Animals “mobbed” together into several large groups, rather than many distinct smaller flocks
What is efficacy
ability to produce desired effect
What are the Regulation of veterinary treatment
- APVMA (Australia), FDA (USA) etc
- International harmonisation, but variation between countries and continents
- Difference between companion animals and food producing animals
- WHP & ESI
- Pharmacokinetics & pharmacodynamics (see toxins lectures in first semester)
- Costs a lot of money (millions) to register each drug (safety, efficacy, chemistry studies etc)
What are some ways in delivering treatment to animals
– oral,
– sub-cutaneous (applied under the skin.)
– intra-muscular,
– intravenous (administered into, a vein or veins)
– transdermal (route of administration wherein active ingredients are delivered across the skin for systemic distribution)
– intra-abdominal,
– intra-ruminal,
– intramammary (breast tissue)
– Topical (eg conjunctival) (applied directly to a part of the body)
– Aural (relating to the ear )
– intravaginal
– inhalation and
– suppository (cone-shaped object that you put in your body)
Different classes to treatment a disease
- Inhibition of cell wall synthesis
- Damage to cell membrane function
- Inhibition of nucleic acid synthesis or function
- Inhibition of protein synthesis
Factors and ways for Inhibition of cell wall synthesis
- Eg. Penicillins, cephalosporins (beta-lactam antibiotics)
- Cell wall = major difference between bacteria and mammalian cell
- Difference in cell wall between gram positive and gram negative (gram +ve = thicker)
Factors and ways for Damage to cell membrane
function
- Polymyxins, polyenes (amphotericin, nystatin), imidazoles (-azole) & monensin
- Damage to cell membrane leads to leakage of cellular contents and cell death
- Polyenes & imidazoles important in fungal therapy (see fungal)
Factors and ways for
Inhibition of nucleic acid synthesis or function
- Nitroimidazoles, nitrofurans, nalidixic acid, fluoroquinolones (-floxacin), novobiocin, firampin, sulfonamides, trimethoprim & 5-flucytosine
- Most act by binding DNA to inhibit replication or transcription (Trimethoprim-sulfonamide inhibit synthesis of folic acid)
Inhibition of protein synthesis
• Tetracyclines, aminoglycosides (-cin),
amiocyclitols (spectinomycin),
chloramphenicol, lincosamides and macrolides ( eg. Erythromycin & others)
• Selectively inhibit bacterial ribosomes compared to mammalian
• Affect either 30S or 50S ribosome
What is the difference between Bacteriostatic and bacteriocidal
• Capable of inhibiting the growth or reproduction of bacteria versus
capable of killing bacteria
• In general a bacteriocidal (kill) antibiotic is preferred where possible
What are the choices of antibiotic
• C & S, location of bacteria • Spectrum • Cidal versus static • Administration form • Duration of treatment • Ability to repeat dosage (wild animals) • Cost • Other – Gut flora – Reactions (birds and procaine)
When do you use antibiotics
front line when other preventives have failed
What are the preventives
– Good diet
– “good” bacteria (ruminal fluid for acidosis)
– environment
What are some drugs for
• Large number of different families of drugs • Some examples – Monensin – Amprolium – Lasolacid – Toltrazuril
What are some drugs against cestodes
- Praziquantel – active against wide range of tapeworms
- Niclosamide (salicylanilide) – used for tapeworms of sheep, cattle horses & poultry (also dogs and cats)
- Some benzimidazoles have moderate activity against tapeworms
What are some drugs against nematodes
- Arsenicals (thiocetarsamide, melarsomine)
- Organophosphates (coumaphos, dichlorvos..)
- Piperazines (piperazine, DEC)
- Salicylanilides (oxyclozanide, closantel etc)
- Benzimidazoles (..dazole)
- Imidazothiazoles (tetramisole & levamisole) & Tetrahydropyrimidines (pyrantel & morantel)
- Avermectins/milbemycins (mectins, MLs)
- Amino-acetonitrile derivatives (AADs)
- Derquantel
What are some drugs against trematodes
• At high dose rates most BZ have moderate kill rates of adult fluke
• Triclabendazole good efficacy against adult and immature stage
• Salicylanilides – highly effective against adult fluke, moderate to poor
against immature
What are some drugs agaisnt arthropods
• Organochlorines – generally banned
• Organophosphates –history of OHS issues, but used
• Synthetic pyrethroids
• Carbamates
• Amermectins/milbemycins
• Formamidines (Amitraz)
• Phenylpyrazoles (Fipronil)
• Nitroguanideines and spinosyns (imidacloprid & spinosad)
• IGRs
– Benzoylphenyl ureas (…urons)
– Triazine/pyrimidine derivatives (cyromazine, dicyclanil)
• Juvenile hormone analogues (methoprene, pyriproxyfen)
What are the consideration for treating individual animal
• Individual veterinary consult (eg sick dog or cat) – treatment directed solely at the level of the individual animal – though including owner and family
What are the consideration for treating groups of animal
• On large properties with a large number of animals at risk of infection of a disease that is very likely to spread, all animals may be treated to reduce spread eg. treating dairy cows for Streptococcus agalactiae
Permutations/combinations of the above two points are common
How are the treatment of individual animal based on
• High value agricultural animals, performance animals and pets often receive individual attention
• Treatment is based on a diagnosis of a particular condition and subsequently choosing an effective treatment for that condition
• If an animal has a high value (either emotional or financial) an owner is more likely to be willing to spend more money on establishing a diagnosis
and aiming for the best treatment
How are the treatment of mob, flock, herd based on
- In some situations a disease may be present at a relatively high level in a group of animals
- Rather than spending large amounts of money on diagnosis of the problem in each individual animal, a representative sample can be chosen and optimal treatment for the group decided
- “Blanket” treatment may then be given eg. “drying off” therapy for dairy cattle at the end of lactation
How is mastitis in dairy cattle treated
- A number of bacteria can cause mastitis in dairy cattle including Streptococcus agalactiae and Streptococcus dysgalactiae
- Cows are often tested each month to assess milk volume and quality – including fat %, protein % and cell count
- Cell count is a measure of mastitis in the dairy cow as when the udder has a problem white blood cells in the milk are increased
- What trigger for treatment?
is it acceptable for owners of animals to do nothing to treat disease in
animals
no
What is the scientific name of scabby mouth/ orf
Parapox virus
What bacteria causes mastitis in dairy
streptococcus agalactiae and streptococcus dysgalactiae
How is milk physically harvested
• Rotary/Herringbone • Robot
