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Mycobacterium bovis

2013-03-28T09:18:15Z

IanMVB: /* Diagnosis */

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Also known as: '''''Bovine TB — Bovine Tuberculosis'''''

== Introduction ==

[[Image:Tuberculosis M bovis.jpg|thumb|right|100px|<center>Tuberculosis caused by M. bovis (Image sourced from Bristol Biomed Image Archive with permission)</center>]] Mycobacterium bovis causes '''tuberculosis''' in cattle. It is a chronic disease characterised by '''granulomatous nodular''' lesions in any organ, although the respiratory system is most commonly affected. The nodules often become necrotic with a caseous centre. The primary lesions may disseminate to involve other body systems.

Inhalation of ruminal gases is the most common route of entry for the mycobacterium organism, and spread of the disease is usually via cow-to-cow contact via aerosol. Cattle can also become infected by ingestion of the causative agent; this is the usual route of entry when the badger is involved, by infecting grazing land or water troughs. Calves with infected dams can become affected via the milk, and intrauterine infection at coitus has been reported.

A higher level of infection is required to establish the alimentary form of the disease and this is reflected by its lower incidence in comparison to the respiratory form. In the respiratory form, the mycobacteria are inhaled, gaining entry to the respiratory system. The organisms are phagocytosed by alveolar [[Macrophages|macrophages]] where they multiple and result in a characteristic [[Granulomatous Pneumonia|granulomatous inflammation]] and tubercle formation. Ultimately, caseous necrosis develops and the nodule ruptures, releasing the organism and infection spreads. The cell-mediated immune system is activated and produces cytotoxic T-lymphocytes, which attack and destroy infected cells, leading to a [[Type IV Hypersensitivity|type IV hypersensitivity reaction]].

Historically bovine TB was a major cause of human TB, but the introduction of tuberculin testing and slaughter, meat inspection at abattoirs, the pasteurisation of milk and the BCG vaccination has dramatically reduced transmission to humans and bovine TB as a cause of human disease is now very low indeed.

The disease is of serious economic importance to farmers because of the stringent control measures, which remain in place. These include the slaughter of infected animals and movement restrictions placed on farms with reactors or inconclusive results.

== Pathogenesis and Pathogenicity ==

The ability of mycobacteria to survive and multiply within macrophages determines whether disease will occur within the host. Survival and multiplication of the organisms in macrophages at primary site of infection happens due to prevention of phagosome-lysosome fusion. Mycobacteria utilize several virulence factors including cord factor or trehalose dimycolate, surface glycolipid, sulfatides, lipoarabinomannan, heteropolysaccharide, heat shock protein, complement, and tubuloprotein. The types of immune responses that are critical in responding to mycobacterial infection are cell-mediated immunity and the delayed hypersensitivity response.

Pathogenicity of mycobacteria depends on their ability to escape phagocytic killing, mostly imparted by the cell wall consitiutents:

*Cord factor (trehalose dimycolate) – surface glycolipid responsible for serpentine growth in vitro.
*Suphatides – surface glycolipid containing sulphur which prevents fusion of phagosome with lysosome. cAMP secreted by the bacteria may also facilitate this.
*LAM – heteropolysaccharide which inhibits macrophage activation by IFNγ and induces macrophages to secrete TNFα which induces fever and IL-10 which suppresses mycobacteria-induced T cell proliferation.
*The wax of the cell wall, peptidoglycans and other glycolipids are responsible for the adjuvant activity – attracts antigen presenting cells.
*Tubuloprotein – important antigen; purified tubuloprotein is the basis of the tuberculin test.

Mycobacteria are released from macrophages and also migrate within macrophages around the body. Waxy cell wall contributes to the host immune response to the mycobacteria and the development of lesions. The host mounts a cell-mediated immune response with activated macrophages and sensitised T cells followed by a [[Type IV Hypersensitivity|delayed-type hypersensitivity response]] with granuloma formation.

== Signalment ==

The disease usually affects heifers or young stock but cases can occur in cattle of any age. TB is more common in dairy herds.

Incidence of the disease has increased over the past 15 years; it is prevalent in '''Wales''' and the '''southwest''' of England but is re-emerging in other parts of the UK such as the west Midlands and northwest England.

Most warm-blooded animals are susceptible to bovine TB and can act as a reservoir for infection. The disease in cattle has been associated with wildlife species in a number of countries; the European badger and red deer in the UK, opossums and ferrets in New Zealand, mule deer, white-tailed deer, elk, and bison in North America and water buffalo in Australia.

== Diagnosis ==

The '''intradermal comparative tuberculin test''' is widely used in the UK for diagnosis of the disease. Two injections are given intradermally in the neck of cattle, an '''avian''' and a '''bovine''' '''tuberculin purified protein derivative''' (PPD). The thickness of the skin is recorded at each injection site. The test is read after '''72 hours''', and the thickness of the skin is remeasured. Interpretation is based on finding a swelling or increase in skin thickness at the site of the injection. A comparison must be made between the reaction to avian and the bovine tuberculin to account for cross reactivity with related diseases, such as atypical mycobacteriosis, or [[Johne's Disease|Johne's disease]].

A single intradermal test is used in many countries but has the disadvantage of giving reactors to avian tuberculosis and Johne's disease.

=== Clinical Signs ===

Location and severity depend on which body systems are affected and the advancement of the disease. Due to the testing and slaughter policy most cases in the UK are identified before development of clinical signs.

==== Respiratory form ====

*Chronic cough- soft and productive
*Tachypnoea
*Dyspnoea
*Dull areas on auscultation of the lungs in advanced cases

==== Alimentary form ====

*Few clinical signs
*Diarrhoea
*Bloat

Mammary involvement is now rarely seen; the uterine form is also uncommon but may result in abortion.

=== Laboratory Tests ===

An [[ELISA testing|ELISA test]] has been developed but is not widely used. The gamma interferon test can also be used for diagnosis of the condition.

Laboratory examination of lesions, lymph nodes and milk can be performed. Lesions contain macrophages, multinucleate giant cells and later a central area of caseous necrosis, giving a cheesy appearance. Tissues can be prepared using Ziehl-Neelson stain. Bacterial isolation requires Lowenstein-Jensen medium.

=== Pathology ===

Findings at post mortem depend on the route of entry of the organism, whether it became generalised or not and the stage of the disease. One or more lymph nodes will display the characteristic granulomatous tubercles. In the respiratory form the mediastinal and bronchial lymph nodes are affected, with lesions in the lungs.

If the mycobacteria disseminated from the primary complex then lymph nodes in other regions will also be affected and there will be multiple small foci of infection on other organs.

Microscopically there are '''epithelioid cells''', with large vesicular nuclei and pale cytoplasm and '''giant cells''', formed by the fusion of macrophages, are found at the centre of tubercles. Surrounding this there is a narrow layer of lymphocytes, mononuclear cells and plasma cells, more advanced cases show peripheral fibroplasia and central necrosis.

== Treatment and Control ==

Treatment is not usually an option due to the chronic nature of the disease, zoonotic potential and test and slaughter policy.

Control in many countries is centred on tuberculin testing with slaughter of reactors and movement restrictions to the premises. Research work continues into the use of vaccination, or a cull strategy for the associated wildlife populations.

== Prognosis ==

Poor.

== Links ==

<big>'''[[Tuberculosis|General Tuberculosis]]'''

'''[[Tuberculosis - Dogs|Canine Tuberculosis]]'''

'''[[Mycobacterium avium|Avian Tuberculosis]]'''
</big>

{{Learning
|literature search = [http://www.cabdirect.org/search.html?rowId=1&options1=AND&q1=%22Mycobacterium+bovis%22&occuring1=title&rowId=2&options2=AND&q2=cattle&occuring2=od&rowId=3&options3=AND&q3=&occuring3=freetext&x=48&y=9&publishedstart=yyyy&publishedend=yyyy&calendarInput=yyyy-mm-dd&la=any&it=any&show=all ''Mycobacteroium bovis'' in cattle publications]
|full text = [http://www.cabi.org/cabdirect/FullTextPDF/2009/20093181590.pdf '''Progress in the development of tuberculosis vaccines for wildlife.''' Buddle, B. M.; Aldwell, F. E.; Corner, L. A. L.; CABI, Wallingford, UK, CAB Reviews: Perspectives in Agriculture, Veterinary Science, Nutrition and Natural Resources, 2009, 4, 030, pp 1-10]
}}

== References ==

*Andrews, A.H, Blowey, R.W, Boyd, H and Eddy, R.G. (2004) '''Bovine Medicine''' (Second edition), ''Blackwell Publishing''
*Blood, D.C. and Studdert, V. P. (1999) '''Saunders Comprehensive Veterinary Dictionary (2nd Edition)''' ''Elsevier Science''
*Merck & Co (2008) '''The Merck Veterinary Manual (Eighth Edition)''' ''Merial''
*http://www.defra.gov.uk/foodfarm/farmanimal/diseases/atoz/tb/

{{review}}

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[[Category:Cattle_Bacteria]] [[Category:Respiratory_Diseases_-_Cattle]] [[Category:Mycobacterium_species]] [[Category:Expert_Review_-_Farm_Animal]] [[Category:Respiratory_Bacterial_Infections]] [[Category:Zoonoses]]

Escherichia coli

2012-11-20T11:30:20Z

IanMVB: /* Pathogenesis */

{{review}}

===''Eschericia coli'' (''E. coli'') overview===
[[File:Ecoli.jpg|200px|right]]
*Member of ''Enterobacteriacae'' family of Gram-negative bacilli
*'''Facultative anaerobe'''
*One of predominant bacterial species in colonic flora
*Colonisation of intestinal tract from environmental sources shortly after birth
*Abundant in the environment
*Most strains have low virulence
*Found in many non-specific, endogenous infections, eg. wound infections, upper respiratory tract infections, infections of the urinary tract, mammary glands and uterus and septicaemia
*An enteropathogen, causing neonatal diarrhoea in young animals and enteric colibacillosis
*Enterotoxigenic ''E. coli'' is the most common cause of diarrhoea in calves, lambs and pigs
*Pathogenic strains possess virulence factors allowing colonisation of mucosal surfaces

===''E. coli'' characteristics===

*Usually motile with flagella and fimbriae
*'''Oxidase negative''' (do not possess cytochrome C oxidase)
*Grow on '''MacConkey agar''' (in presence of bile salts), producing pink colonies
*'''Haemolytic activity'' on blood agar characteristic of certain strains
*'''Lactose fermenter'''
*Reduce nitrates to nitrites and ferment glucose to produce acid and gas
*Possess a lipopolysaccharide ('''O''') antigen, a flagellate ('''H''') antigen, polysaccharide capsule ('''K''') antigens and fimbrial ('''F''') antigens
*Epidemiological typing of ''E. coli'' uses antigen combinations, eg. O125:K12:H42

===Pathogenesis===

*Virulence factors include capsules, endotoxin, enterotoxins and colonisation factors
*Capsular polysaccharides produced by some strains prevent phagocytosis and interfere with complement
*Endotoxin is a lipolysaccharide component of the cell wall of Gram-negative bacteria, composed of lipid A, a core polysaccharide and various side chains
*'''Endotoxin''' is realeased when bacteria die, and causes endothelial damage leading to [[Disseminated Intravascular Coagulation|'''disseminated intravascular coagulation''']] and '''endotoxic shock'''; it is also a '''pyrogen'''
*Enterotoxins, verotoxins and cytotoxic necrotising factors produced by many pathogenic ''E. coli''; these produce cell damage at their site of action
*'''Alpha-haemolysin''' may increase iron availability for invading organisms
*'''Siderophores''' are made by certain pathogenic strains, and are responsible for iron aquisition; they include aerobactin and enterobactin

==Extra-intestinal infection==

*Soft tissue infections in adult animals
*Pathogenesis:
**Produces an alpha-haemolysin which may be cytotoxic
**Iron aquisition system
**K antigens prevent phagocytosis or mimic host antigens and resist complement
**Fimbriae permit adhesion to mucosal surfaces
**May enter blood to cause septicaemia
*Clinical infections:
**'''Urogenital tract infections'''
***Most common organism infecting urinary tract
***Ascending infections of urinary tract
***Causes pyometra in the dog and cat and [[Pyelonephritis|pyelonephritis]]
***Cystitis in the bitch
***Prostatitis in dogs via opportunistic infection
***Colonisation of mucosa aided by fimbriae
**'''Mastitis'''
***Opportunistic infection of mammary glands of sows and cows
***Endotoxaemia in the acute form often fatal
***Death within 24-48 hours during peracute disease
***Animals depressed with sunken eyes
**[[Colibacillosis|'''Colibacillosis''']]:
***Avian:
****Septicaemia in newly-hatched chickens
****Infection enters via faecal contamination of the egg surface or via the ovary of the hen
****Infection enters via the respiratory tract
****A bacteraemia develops
****Acute colisepticaemia, subacute fibrinopurulent serositis or chronic granulomatous disease of the viscera
****Occurs in older birds via inhalation of ''E. coli'' in dust; respiratory infection spreads to the blood to cause acute colisepticaemia
****Airsacculitis, pericarditis and perihepatitis during acute phase
****Often secondary to virus or [[:Category:Mycoplasmas|''mycoplasma'']] infection or environmental stress
**'''Colisepticaemia''':
***Systemic disease in young calves, piglets, foals, lambs
***Penetration of intestinal mucosa and entrance into the blood
***Invasive strains survive the host defences
***Virulence related to adhesive properties, complement resistance and ability for iron aquisition
***Ammonia, dust, viral infections and temperature changes enhance likelihood of disease
**[[Oedema Disease|'''Oedema disease of pigs''']]:

**'''Watery mouth of lambs''':
***Affects lambs under three days old
***Lack of colostrum allows collonisation and overgrowth of ''E. coli'' in the small intestine
***Systemic invasion by ''E. coli''
***Absorption of endotoxin leads to death
***Severe depression, anorexia, salivation and abdominal distension
***Morbidity and mortality high
** [[Inflammatory Bowel Disease#Histiocytic Ulcerative Colitis|Histiocytic ulcerative colitis]] in the dog and cat.
** Causes [[Peritonitis - Cats and Dogs|peritonitis in dogs]] and [[Peritonitis#In pigs|peritonitis in pigs]]
**Found in [[Osteomyelitis|osteomyelitis]]
**Associated with neonatal [[Infectious Arthritis#In Cattle|polyarthritis of calves]]
**In [[Deep Pyoderma|deep pyoderma]]
**Found in [[Infectious Arthritis#In Horses|arthritis of horses]]

==Intestinal infection==

*''E. coli'' is part of the flora of the large intestine, but is not usually found in the small intestine
*Some strains possess fimbrae which attach the bacteria to the small intestinal epithelium of particular animal species
*''E. coli'' may cause diarrhoea via attaching and effacing lesions, where bacteria adhere intimately to the enterocyte, and cause localised effacement of the brush border microvilli; the epithelial erosion causes [[Haemorrhage#Dysentery|dysentery]]

*'''Enterotoxigenic ''E. coli'' (ETEC)''':
**General:
*** Contributes to [[Calf Diarrhoea, Undifferentiated Neonatal|undifferentiated neonatal calf diarrhoea]], a mixed viral enteritis in calves, also known as enteric colibacillosis
***Causes scours in pigs, calves and lambs
***'Traveller's diarrhoea' in humans
**Pathogenesis:
***Oral infection, intestinal colonisation and toxin production
***Fimbrial antigen or colonisation factor antigens (CFAs)determine species specificity
***Fimbrial adhesins allow bacteria to attach to mucosal surfacesin the small intestine and lower urinary tract; this prevents expulsion by peristalsis and flushing of urine
***K88 (F4) is associated with adhesion to the small intestinal mucosa of pigs
***K99 (F5) associated with adhesion in pigs and cattle (these fimbrial adhesins were originally thought to be capsular (K) antigens)
***The '''fimbriae are encoded by plasmids'''
***These strains carry a plasmid which encodes an enterotoxin
***Two types of '''enterotoxin: heat-labile (LT) and heat-stable (ST) toxins'''
***The '''plasmids''' which produce these toxins are '''responsible for the pathogenicity''' of these strains
****'''LT'''
*****An oligometric toxin composed of an enzymatically-active A subunit (30KDa; 2 fragments - A1 and A2) and 5 identical B subunits (12KDa) forming the binding portion (B oligomer)
*****It attaches to the brush border of the epithelial cells of the small intestine
*****Causes ADP-ribosylation of the stimulatory subunit of guanine nucleotide binding proteins of the adenylate cyclase complex in eukaryotic cell membranes
*****This causes irreversible activation of adenylate cyclase in target cells
*****This raises the cAMP level and causes hypersecretion of water and chloride ions into the lumen of the small intestine and inhibits reabsorption of sodium
****'''ST'''
*****Activates guanylate cyclase in enteric epithelial cells, stimulating fluid secretion
**Clinical signs:
***The gut becomes distended with fluid and a [[Diarrhoea#Secretory Diarrhoeas|secretory diarrhoea]] which lasts several days results
***Watery diarrhoea, dehydration, acidosis, death
**Immunity:
***LT is antigenic
***Immunity is developed via production of antibody to LT protein and fimbrial antigen
***Parenteral vaccination of pigs and cattle protects offspring from scours via antibody production in the colostrum (passive immunity)
***ST is not immunogenic; it is small, with only 19 amino acids

*'''Enteropathogenic ''E. coli'' (EPEC)''':
**Attaching and effacing strains of ''E. coli''
**Attach to small intestinal epithelial cells and cause necrosis of enterocytes and stunting and fusion of villi
**Possess ''E. coli'' adherence factor plasmid
**An adhesin, intimin is required for attachment to enterocytes
**Secrete signalling proteins that activate a tyrosine kinase, causing rearrangement of cytoskeletal proteins and effacement of microvilli
**Intracellular calcium levels increase and production of protein kinase C causes loss of chloride ions and water from the intestinal epithelial cells
**Diarrhoea results

*'''Enteroinvasive ''E. coli''''':
**Cause colisepticaemia in calves during their first week of life; occasionally in lambs, piglets and puppies
**Infection via ingestion or umbilicus; inadequate colostrum increases susceptibility
**Invade epithelial cells of small intestine by inducing endocytosis
**Traverse gut wall to lamina propria and enter lymphatics
**Resistant to complement-mediated killing
**Bacteraemia or septicaemia and endotoxaemia
**Widespread petechial haemorrhages of organs and serosa
**Abscesses, pneumonia in long term
**Death occurs in absense of treatment

*'''Enterohaemorrhagic ''E. coli''''':
**Possibly carried by cattle
**Produce shiga-like toxin, a vero toxin
**Plasmid-coded fimbriae important for virulence
**Intimin produced allowing intimate attachment to intestinal epithelial cells
**Strains do not product LT or ST and are not enteroinvasive
**Attaching and effacing lesions, unrelated to toxin production
**[[Disseminated Intravascular Coagulation|Disseminated intravascular coagulation]] and thrombus formation
**''E. coli'' O157:H7 causes haemorrhagic collitis-haemolytic uraemic syndrome in humans

*'''Cytotoxin necrotising factor-producing ''E. coli'''''
**Infrequently cause diarrhoea in calves, pigs and humans
**Important virulence factors include toxin and fimbriae

==in cattle==

*Neonatal polyarthritis:

**[[Escherichia coli|'''''Coliforms''''']]
***Localises in joints and meninges in severe non-fatal neonatal colibacillosis
***May remain as chronic arthritis in larger joints

[[Category:Enterobacteriaceae]]
[[Category:To_Do_-_Bacteria]]

Staphylococcus aureus

2012-10-20T17:43:47Z

IanMVB: /* Botryomycosis */

===Overview===
''Staphylococcus aureus'' is a species of major veterinary significance as it can infect most of the common domestic species. Though transfer between species and between animals and man is limited there is still significant levels of ''S. aureus'' existing in the environment to pose a threat if not properly controlled. It is a major cause of mastitis in cattle, sheep, goats and horses.

===Characteristics===
''S. aureus'' has a standard staphylococcal morphology but varies somewhat in its biochemistry.

===Bovine mastitis===

*''S. aureus'' is a common cause of mastitis in cattle worldwide
*Most infections subclinical
*Systemic infection can occur with peracute and gangrenous forms
*In gangrenous mastitis, the quarter may become necrotic and slough off; alpha toxin causes necrosis of smooth muscle in blood vessel walls, reducing blood flow to the affected quarter, and causes release of lysomal enzymes from leukocytes

===Tick pyaemia===

*Infection of lambs with ''S. aureus'' in hill-grazing areas of the UK
*Lambs carry ''S. aureus'' on their skin and nasal mucosa; infection via skin trauma including tick bites
*''Ixodes ricinus'' tick acts as a vector for ''[[Ehrlichia phagocytophila]]'', which causes immunosuppression in lambs, predisposing to staphylococcal infection
*Acute septicaemia and death or localised abscess formation in many organs
*Arthritis, posterior paresis and ill-thrift
*Microscopic identification of bacteria in pus and isolation of ''S. aureus''
*Prophylactic antibiotics e.g. tetracyclines initiated at 1 week of age may prevent infection
*Tick control important

===[[Botryomycosis]]===

*Chronic, suppurative granulomatous condition
*''S. aureus''
*Occurs following castration of horses due to infection of stump of spermatic cord
*Occurs in mammary tissues of sows
*Mass of fibrous tissue containing pus and sinus tracts

===Other infections caused by ''S. aureus''===

*[[Bacterial skin infections - Pathology#Impetigo|Impetigo]] in cattle and pigs
* [[Oedema#Permeability type|Permeability types of pulmonary oedema]]
*Haemorrhagic disease by [[Platelet Abnormalities|secondary thrombocytopenic disease]]
*May infect [[Infectious Arthritis#In Sheep|joints of sheep]]; [[Infectious Arthritis#In Pigs|arthritis in pigs]]
*Dermatitis in sheep and goats
*Arthritis and septicaemia in turkeys
*Bumblefoot and omphalitis in chickens

* 30% strains of ''[[Staphylococcus aureus]]'' produce potent enterotoxin. T
** Protein and heat-stable
** Responsible for staphylococcal food poisoning in man.
* Every reason to assume that acute gastro-intestinal disturbance in small animals may be caused by these enterotoxins BUT not well documented.
* Symptoms last 24-36 hours and include:
** Acute vomiting
** Diarrhoea
** Pain
* The enterotoxins are superantigens.
** Induce release of cytokines from lymphocytes

[[Category:Staphylococcus species]][[Category:Cattle Bacteria]][[Category:Sheep Bacteria]][[Category:Pig Bacteria]]
[[Category:To_Do_-_Bacteria]]
[[Category:To Do - Major]]