Zoonoses Flashcards
Explain the concept of “One Health.”
Relationship between animal and human health and disease
Positives of animal interactions: o Psychological well-being, companionship o Food, nutrition o Warmth and protection o Power and transportation o Fertilizer
Potential threats:
o Environmental hazards
o Traumatic injuries
o Infectious diseases
Define the term zoonosis and explain the role of animals in human disease.
Definitions:
1) Classic: disease caused by infectious agents that are transmitted from animals to humans
2) Broader: disease caused by infectious agents that are transmitted from animals to humans OR are shared by animals and humans
The role of animals in zoonotic diseases:
Animals = direct source of infection
• Ex: bite wounds, rabies, plague, tularemia, bartonellosis, brucellosis
Animals = indirect source for contamination of food or water supplies
• Ex: salmonellosis, campylobacteriosis, yersiniosis, leptorspirosis
Animals and humans share the infection
• Ex: Lyme disease, blastomycosis, West Nile fever, equine encephalitis, leishmaniasis, Chagas disease
Bartonellosis: characteristics
Bartonella henselae (Rochalimaea henselae) o 2 different genotypes (genotype II may be more pathogenic for humans)
Gram Stain:
o Curved
o Gram negative rods
Characteristics: o Slow-growing, motile o Oxidase and catalase-negative o Grow best at 35°C with CO2 o Grow on chocolate-, rabbit-heart-, or Columbia-blood agar
Other Bartonella species pathogenic for humans:
o B. clarridgeiae, koehlerae, vinsonii, washoensis, elizabethae, alsatica, rochalimae and tribocorum
Bartonellosis: clinical disease
Papules or pustules at site of scratch/bite
o 4-6 days after wound
o Persistent, non-healing wound
Regional lymphadenopathy (7-50 days after)
o >90% of patients
o Histology: necrotizing, granulomatous inflammation, micro-abscess formation
On biopsy:
• 26% nodes = evidence of neoplasia
• 4% = evidence of Mycobacterium infections
Fever (<29%)
Chronic systemic manifestations: o Endocarditis o Osteomyelitis o Uveitis and other eye manisfestations o Prolonged bacteremia and fever o Breast abscesses
CNS diseases:
• Includes: cerebral arteritis, stroke, encephalitis, seizures, coma; myelitis
• Evidence of headaches and/or neurologic disease with or without cognitive dysfunction in patients with cat or biting insect contacts
• Association with Bartonella seropositivity or bacteremia being referred to neurologists/rheumatologists
• Neurologic symptoms, myalgia, arthropathy
• May contribute to neurocognitive decline in AIDS (AIDS dementia)
Bartonellosis: risk factors
Children < 10 years = highest prevalence of CSD (57-80% cases)
More likely to develop complications:
• Persistent fevers and fevers of unknown origin
• Parinaud’s oculoglandular syndrome: Ocular granuloma or conjunctivitis, Preauricular lymphadenopathy
• Spread to abdominal lymph nodes, liver/spleen (7%), bones
• Encephalitis (12%): 1-6 weeks after onset of lymphadenopathy; Seizure or coma may occur
Immunocompromised patients
1) Bacillary angiomatosis:
• Bartonella stimulates vEFG and angiogenesis
• Lobular proliferation of small blood vessels and inflammatory infiltrates
2) Peliosis hepatitis:
• Blood-filled cystic lesions develop in liver (sometimes spleen)
• Associated with: hepatomegaly, abdominal pain, nausea
3) Hepatitis and splenitis
• Granulomatous
• Necrotizing
• Can progress to spontaneous rupture and hemoperitoneum (bleeding into peritoneum)
Bartonellosis: vectors
Cats!
Widespread infection in cats
• 15-30% seropositive (especially in southeastern U.S.)
• Maintain prolonged (up to 22 months) bacteremia
Often asymptomatic
o In 90% human CSD cases = cat contact
• 75% = scratch or bite
• Greater risk = kittens (more likely to cause scratches)
Other animal vectors also possible
Bartonellosis: diagnosis
Clinical presentation + history of animal contact + lab measure:
Serologically: IFA, ELISA assays
• Single high IgG titer
• 4x rise in IgG titers
• Positive IgM titer
Culture
• Confirmation and exclusion of other potential causes of lymphadenitis
• Skin lesion punch biopsies
PCR for bacteremia
Bartonellosis: treatment
Adenopathy resolves in 2-6 months
Antibiotics = prevent other complications from occurring (but do not alter course of disease significantly)
• Azithromycin for CSD
• Doxycycline or erythromycin for 8-12 weeks for bacillary angiomatosis
Aspirate nodes if fluctuant (rarely)
Bartonellosis: prevention
o Avoid rough play with cats
o Wash scratches/bites well (bacteria present in saliva)
o Flea control
o Antibiotic therapy in cats = unlikely to immediately eliminate organism and reduce risk of transmission
o Negative serologic test in cat = highly predictive that cat is NOT bacteremic
• Immune-compromised patients should adopt only seronegative adult cats
Plague: causative organism and characteristics
Yersinia pestis
o Gram-negative bipolar rod
Characteristics:
o Aerobic growth on most media (including blood agar and MacConkey’s)
• Forms small colonies on MacConkey’s
o Oxidase-negative, catalase-positive
o Does NOT ferment lactose
o Does NOT utilize citrate, urease or indole
o Non-motile
o Grows better at 28°C than at higher temperatures
o Triple-sugar-iron (TSI) slants = produces alkaline slant and acid butt
Plague: modes of transmission/reservoir
Cause of Black Death in Middle Ages
Locations:
o Currently: Asia, Africa, Andean countries of South America
o In U.S: Western states: New Mexico, Arizona, Colorado, Texas, California, Nevada
Reservoir:
o Primarily rodents (rats)
o Seasonal summer pattern in temperate regions
Transmission via:
Fleas from infected rodent
• Blood meal in foregut clots
• Y. pestis expresses phospholipase enzyme = able to survive in flea midgut → replicates
• Blockage of gut → regurgitation of organisms at next feeding
Ingestion of infected rodents (Ex: cats)
• Also = ingestion of guinea pigs by humans in Andes
Direct contact with blood, pus, aerosols
At risk:
o Veternarians = handling infected cats
Plague: clinical forms
Bubonic plague o Most common (81% cases) o 2-8 day incubation o High fever, headache, malaise o Warm, painful, swollen lymph nodes (“buboes”) • Hemorrhagic necrosis on histology o May be tachycardic and hypotensive Meningitis if not treated: • Fever, headache, meningismus • PMN pleocytosis in CSF
Septicemic plague o Hematogenous spread throughout body • Y. pestis replicates within mononuclear leukocytes o Shock, DIC and death within 2 days o 30% mortality if untreated
Pneumonic plague
o Lung infection after inhaling organism or hematogenous spread
o Cough (often with hemoptysis) and chest pain
o Bronchopneumonia and lung consolidation
o 100% fatal if untreated
o Potential as a bioterrorism agent
Plague: diagnosis
Gram statin of an aspirate or bacterial culture
• Bipolar rod (NOT a diplococcus)
• Use Wayson’s or Wright’s stain = accentuates bipolar look
• Fluorescent Ab staining can confirm
Plague: treatment
Antibiotics:
Aminoglycosides: DOC is streptomycin
• Alternative = gentamicin
Also effective: tetracyclines, fluoroquinolones, chloramphenicol
• Recommended for meningitis, pleuritis, endophthalmitis, myocarditis cases
Levofloxacin recently approved
NOTE: penicillins (beta-lactams) NOT effective
Aspirate buboes if fluctuant
Plague: prevention
Vaccination Formalin-inactivated vaccine available • Travelers to endemic areas • People in high risk occupations Cat vaccination developed but not commercially available
o Insecticides
o Rodent control
o Personal protective devices
