121. Diseases caused by Rhodococcus equi and dermatophilosis. Flashcards
1
Q
Exudative dermatitis caused by Dermatophilus congolensis - exudative dermatitis?
A
Exudative dermatitis caused by Dermatophilus congolensis – Exudative dermatitis
Dermatophilosis:
- Exsudative,
- pustular dermatitis of ruminants and horses
- (human also susceptible)
Occurrence
- Worldwide: Tropical, subtropical regions: most prevalent (West and Central Africa, Caribbean islands)
- Australia, New Zealand: half of the livestocks are infected
- EU: regularly introduced
2
Q
Aetiology - Dermatophilus congolensis?
A
Aetiology - Dermatophilus congolensis
- Habitat = Skin of carrier animals (sheep, goat, cattle, horses)
- Gr+ branching filaments → can break down into flagellated cocci (known as motile zoospores – high
- resistance, survive for months in dry environment)
- Obligate aerobic, capnophilic (10% CO2), Fastidious (blood agar), 3-4 days
- 2-5 mm wrinkled yellow colonies (carotenoid pigments); Strong β-haemolysis on blood agar
- Virulence factors: phospholipases, proteases, alkaline ceramidase
- Zoospores can survive up to 3 years in dry scabs (on skin surface)
3
Q
Epidemiology of Dermatophilus congolensis?
A
Epidemiology
- Susceptibility: cattle, sheep, goat, horse, camel, human
- Introduction: symptom free infected animals, wool, skins, clippers, human
- Predisposing factors
- (facultative pathogens):
- skin lesions (trauma),
- persistent wetting (heavy prolonged rainfalls),
- malnutrition, pregnancy, ectoparasites (Amblyomma variegatum)!
- → Activation of dormant
- flagellated zoospores!
- (produce EC enzymes → exudative dermatitis)
4
Q
Pathogenesis of Dermatophilus Congolensis?
A
Pathogenesis
- Wet, soggy, damaged skin → exsudative, pustular dermatitis (vesicles, scabs)
- Only the skin is affected!
- Incubation period: 1 month
5
Q
Clinical findings of Dermatophilus congolensis?
A
Clinical findings
- Lesions: on the dorsum of animals
- Papules detectable only by palpation
- Serous exudate causes matting of hairs giving them a tufted appearance
- Irregular elevated crusty scabs
- Tufts of hair can be readily plucked from the lesions along with adherent scab material and underlying
exudate
- Lesions may resolve spontaneously within a few weeks (especially in dry environment)
- In severe infections lesions may be extensive, fever, anorexia, death (10- 15%) – calves, lambs
- Differentiate from ringworm
6
Q
Diagnosis and treatment of Dermatophilus Congolensis?
A
Diagnosis
- Clinical findings
- Skin scrapings – smear
- Bacteriology (wrinkled, yellow, beta-haemolysing colonies)
Treatment
- Dry, clean bedding; Dry environment
- Parenterally (IM) administered AB (oxytetracycline, penicillin-streptomycin, erythromycin) on 3 consecutive
days (Topical treatment alone are ineffective!)
• Infected herds must be isolated!
7
Q
Prevention and Public health aspects of Dermatophilus Congolensis?
A
Prevention
- Minimizing the effects of predisposing factors + early treatment of clinical cases
- Prevention of skin lesions
- Anti-parasitic treatment (tick infestation must be reduced by dipping)
- Dry environment
- Clinically affected animals should be isolated and treated promptly!
- Prophylactic use of long-acting tetracyclines in endemic regions
Public health aspects
- Human is not very susceptible! – Zoonosis
- Close contact with infected animals (wearing disposable gloves!)
- Prevention of skin lesions
- On hands: papules, exudation, scab formation
- Spontaneous healing within 2 weeks
8
Q
Rhodococcus Equi pneumonia of foals Occurence?
A
Rhodococcus equi pneumonia of foals
- Suppurative bronchopneumonia of 1 to 4 months old foals.
- Abscesses in the lung; Granulomatous ulcerative enterocolitis; Mesenteric lymphadenitis; Arthritis
Occurrence
- R. equi - in the soil everywhere!!! (like Listeria/Nocardia)
- Disease: endemic (year by year – significant losses) OR sporadic OR not present
- Background?: soil (pH or other features), weather, dust, breeding technology, virulence of agent, genetic
susceptibility
9
Q
Aetiology R equi ?
A
Aetiology – R. equi
- Soil microorganism
- Gr+, polymorphic (branching filaments/rods/cocci); Not fastidious (nutrient agar)
- Salmon-pink pigments, mucoid (capsule); Non haemolytic colonies; Obligate aerobic, non-motile
- Catalase +, oxidase +, OF: -
- CAMP test: positive (S. aureus) – haemolysis
10
Q
Epidemiology R . Equi ?
A
Epidemiology
- Infection is acquired by inhalation of dust contaminated w/ virulent
- (vapA+: vap = virulence associated protein)
- R. equi strain! (Vap protein is encoded in a plasmid)
- Virulent strains can accumulate in the soil!!!
- R. equi is responsible for 10% of foal mortality, 45% of pneumonia cases
- Morbidity rate: 5-17%, mortality rate: up to 80%
- Predisposing factors:
- Age: foals are susceptible under 4 months of age (1-3 months!!)
- Summer time (May-August)
- Dusty conditions, windy, dry weather
- R. equi can propagate in the gut up to 8 weeks of age
- Virus infections (EHV-2)
- High foal density, immunodeficiency, genetic predisposition
11
Q
Pathogenesis of R.equi?
A
Pathogenesis
- Route of infection: inhalation (dust); per os, umbilical, intrauterine (abortion)
- Alveolar macrophages – inhibit phagosome-lysosome fusion – propagation – cell lysis – tissue destruction
- o → purulent bronchopneumonia
- Gut: in the cells of Peyer patches → ulcers → ulcerative enteritis / arthritis
- The course of the disease is longer than 3 weeks in the half of the cases.
12
Q
Clinical findings of R. equi ?
A
Clinical findings
- Chronic, purulent bronchopneumonia with abscess formation + purulent lymphadenitis
- Fever (38.8-41.5°C);
- Coughing, dyspnoea, anorexia; Weight loss, nasal discharge
- Auscultation of the lungs: loud, moist rales
- Ulcerative enterocolitis, typhlitis, purulent lymphadenitis
- 50% of pneumonia cases
- Majority: no clinical signs (fever, diarrhoea, colic)
- Aseptic polysynovitis, polyarthritis
- 30% of pneumonia cases
- Tibiotarsal and knee joint is affected - Lameness
13
Q
Pathological findings of R.equi?
A
Pathological findings
- Purulent bronchopneumonia with abscesses
- Thin encapsulated abscesses with thick, greyish-reddish pus
- Enteritis – multifocal (Peyer patches) ulcerative enterocolitis and typhlitis,
- with purulent mesenterial lymphadenitis
14
Q
Diagnosis of R.equi?
A
Diagnosis
- History of the disease on the farm
- Age of the affected foals (1-3 months)
- Clinical signs: fever, dyspnoea, arthritis
- Laboratory findings: neutrophil leukocytosis, hyperfibrinogenaemia – up to 10 g/l (N: 1-4 g/l)
- Cytological and bacteriological examination of respiratory secretions, tracheal aspirates
- Nutrient agar: Mucoid, shiny colonies, like water drop; Blood agar: no haemolysis
- X-ray, Ultrasonography
- Pathology, bacteriological examination
15
Q
Treatment of R. equi?
A
Treatment
- Rifampicin + a macrolide AB ʹ
- Clarithromycin, azithromycin, erythromycin
- Bacteriostatic, synergistic effect, lipid soluble, concentrate in macrophages, L chance of AB resistance
- Give for 4-10 weeks
