Zoonotic infections

Introduction

• Risk factors for zoonotic infection
  • Agricultural workers
  • Animal processing
  • Outdoor enthuasiasts
  • Pet owners
  • Professionals: Vets, animal researchers/handlers
  • Immunocompromised

Tickborne infections

• Consider in differential of any nonspecific febrile illness, especially if a rash exists
• Patients often do not recall tick bite
• Tick removal
  • Viscous lignocaine to site to kill tick and anaesthetise area
  • Grab tick by head and pull out all parts
    • Can do with forceps OR suture looped around head
    • If part left in leads to granulomatous reaction
  • Cleanse and disinfect skin

Tickborne infections

• Tick paralysis
  • Only the scrub tick in eastern Australia secretes paralysing toxin
  • Tick bites are painless
  • Tend to be in moist, warm areas on body
  • Anaphylaxis can occur early but is rare
  • Tick paralysis takes days and presents as ascending paralysis
  • Important differential of ataxia in children and GBS in anyone
  • May mimic Bell’s palsy

Tickborne infections

• Rickettsial infections
  • Present as non-specific febrile illnesses with generalised rash
  • Fever may be preceded by localised tender lymphadenopathy with eschar at tick site
  • Australian tick typhus (Rickettsia australis, Rickettsia honei)
  • Scrub typhus (Orientia tsutsugamushi)
  • Murine typhus (Rickettsia typhi)
  • Doxycycline 100mg BD for  7 days

Tickborne infections

• Lyme disease
  • Borrelia burgdorferi
  • Fever, headache, fatigue, myalgia, arthralgia and erythema migrans
    • Small red spot progressing to bull’s eye lesion
  • Neurological and cardiac sequelae

Zoonotic encephalitis

• Mostly arboviral (e.g. Japanese Encephalitis)
• Also seen with Bartonella henselae, Brucella canis, borelliosis, Coxiella burnetii, Listeriosis, Leptospirosis, Lyme disease, psittacosis and toxoplasmosis

Zoonotic meningitis

• Brucellosis, listeriosis, plaque, salmonellosis, tularaemia, leptospirosis, Lyme disease, Coxiella burnetii, psittacosis

Zoonotic respiratory disease

• Pharyngitis
  • Recurrent culture-proven streptococcal pharyngitis can be from household pet
    • Family pet may require course of antistreptococcal antibiotic
• LRTI
  • Inhalational anthrax (Bacillus anthracis)
    • Handling unsterilised imported animal hides or raw wool
    • Mediastinitis without alveolar involvement and not a true pneumonia
  • Brucellosis (Brucella)
    • From unpasteurised dairy or inhalation of aerosols in slaughterhouse
  • Psittacosis (Chlamydia psittaci– parrot fever)
    • Causes atypical pneumonia

Zoonotic respiratory illness

• Q fever
  • Coxiella burnetii is a rickettsial infection from inhalation
  • Shed in urine, afterbirth and faeces of domesticated farm animals
  • Often self-limiting disease
  • May present with pneumonia, pericarditis, myocarditis, endocarditis, granulomatous hepatitis

Zoonotic respiratory illness

• Pasteurellosis
  • Pasteurella multicoda
  • Endemic to normal oral flora of dogs and cats
  • Can result in necrotising infection of bite wounds, bronchitis, bronchopneumonia and suppurative pleural effusion

Zoonotic respiratory illness

• Pulmonic plague (Yersinia pestis)
• Influenza
  • Migrating aquatic fowl are thought to be reservoir of Influenza A
• Hantavirus
  • Rodent urine/faeces/saliva
  • Inhalation or contact with urine or bite
  • Acute renal failure with thrombocytopaenia and flulike illness

Zoonotic GI illness

• Zoonotic gastroenteritis
• Hepatitis E
  • May be contracted from consumption of raw or undercooked meat of infected wild animals (boar, deer, domestic pigs, cattle, sheep, goats and ducks

Zoonotic dermatological disease

• Bacterial
  • Cutaneous anthrax, Bartonella henselae (catscratch)
• Fungal skin infections
  • Blastomyces dermatitidis (Cutaneous blastomycosis)
  • Sporothrix schenkii (sporotrichosis)
  • Both seen in dog and cat owners

Zoonoses from household pets

• Helminths
  • 50% of dogs have at least one intestinal parasite and 15% of adult dogs actively shed Toxocara canis
  • Usually subclinical in humans but may see eosinophilia on peripheral bloods
• Toxoplasmosis
  • Cats host intracellular protozoan Toxoplasma gondii
  • Human toxoplasmosis from uncooked or raw meat (pork or mutton containing cysts), ingestion of oocytes from cat faeces, or transplacental
  • Transplacental can cause chorioretinitis, hydrocephalus,  hepatosplenomegaly and/or thrombocytopaenia (in 10%)
• Leptospirosis
  • Mainly from dogs

Brucellosis

• Aka Mediterranean/Malta fever
• Flu-like illness in those with risk factors
  • Feral pig hunters
  • Overseas travelers
  • Migrants
• Occurs through exposure to Brucella suis from pigs or from unpasteurized dairy in countries where Brucellosis occurs in animals (not Australia)
• Depression is common and severe

Brucellosis

• Incubation phase
  • 2-4 weeks
• Acute phase
  • Fever, sweats, fatigue, hepatosplenomegaly, depression, arthralgia (especially sacroiliitis)
  • Rarely causes meningitis, endocarditis, pneumonia
• Chronic phase
• Management
  • Dual doxycycline and gentamicin

Bartonella henselae

• Cat scratch disease
• Non-painful blister then papule at site of scratch/bite with subsequent painful regional lymphadenopathy about 2 weeks later
• 3-14 days incubation
• Associated arthralgias, malaise, headache
• A minority suffer liver, spleen, eye and CNS involvement
• Lymphadenopathy can persist for months
• Consider in fever of unknown origin
• Serology is first-line test
• Azithromycin + Rifampicin if invasive disease

Q fever

• Coxiella burnetii
• Acute infection
  • 20 day incubation period
  • Flu-like illness
  • Mostly mild pneumonia
  • Hepatitis/acute endocarditis can occur
• Persistent localized infection
  • May occur as endocarditis, bone/joint infection

Q fever

• Risk factors
  • Contact with farm animals
  • Residing downwind from farms/contaminated manure/straw/dust
  • Endemic region
  • Lab workers exposed
  • Abattoir workers
• Diagnosed by serology
• Treated with doxycycline

Last Updated on October 2, 2020 by Andrew Crofton