Zoonotic Infections

zoonosis

An infectious disease transmitted from non-human animals to humans, possibly causing mild to severe symptoms or death.

60% of all human infectious diseases; 75% of emerging ones

What percentage of human infectious diseases originate from animals?

Zooanthroponoses

Humans to animals

Anthroponozoonoses

Animals to humans

Euzoonoses

Humans are obligatory hosts

Amphizoonoses

Bidirectional transmission between humans and animals

Direct contact with animal body fluids
Indirect contact via contaminated environment
Vector-borne (e.g., mosquitoes, ticks)
Food and waterborne

What are the common modes of transmission of zoonoses?

Global Early Warning System (GLEWS)

Name global programs that address zoonotic diseases.

Sporothrix schenckii
soil, plant matter, and decaying vegetation

What is the etiologic agent of sporotrichosis and its source?

Mycelial form at 25°C: septate hyphae, daisy-like conidia
Yeast form at 35-37°C: cigar-shaped budding cells

Describe the dimorphism of S. schenckii.

gp70 (adherence), gp60 (diagnostic marker), SsCBF (detects IgG)

Name key virulence factors of Sporothrix schenckii.

Fixed cutaneous
Lymphocutaneous
Pulmonary
Osteoarticular
Disseminated

List the clinical forms of sporotrichosis.

Fixed Cutaneous Sporotrichosis

This form is localized to the inoculation site, which is typically at exposed areas such as the fingers, hands, and limbs
Lesions can appear as ulcerative, verrucose (wart-like), acneform, papular, or erythematoid (reddish) on the face, neck, or trunk
They manifest as painless nodules that can become palpable and ulcerate, potentially discharging purulent (pus-like) or serous (clear) fluid

Lymphocutaneous Sporotrichosis

This is characterized by the traumatic inoculation of the fungus into the skin, leading initially to nodular lesions that ulcerate
Patients are usually afebrile (without fever) and experience minimal pain
Primary lesions develop at the implantation site
Secondary lesions then appear along lymphangitic channels, starting as painless nodules that become palpable and ulcerate

Pulmonary Sporotrichosis

This form is rare and occurs due to the inhalation of Sporothrix conidia
Symptoms are non-specific and may include weight loss, cough, sputum production, and fever
Lesions are typically found in the upper lobe of the lungs
It can be fatal if left untreated, potentially leading to massive hemoptysis (coughing up blood) due to the lung lesions
It is often associated with individuals who have COPD (Chronic Obstructive Pulmonary Disease) and alcoholics

Osteoarticular Sporotrichosis

Results from direct inoculation of the fungus or hematogenous spread (spread through the bloodstream)
Cutaneous lesions are usually present on the limbs, near the affected joints
The infection is confined to the long bones near the affected area
It is characterized by stiffness and joint pain, commonly affecting the elbow, knee, ankle, and wrist
This form can occur approximately 10 years after the initial traumatic implantation

Disseminated Sporotrichosis

This is the most severe form and occurs most commonly in individuals with a history of alcohol abuse or those who are immunocompromised, especially AIDS patients
It is marked by multiple, painless cutaneous or subcutaneous nodules
It can also lead to ulcers or abscesses in various organs and systems, including muscles, joints, eyes, bones, the gastrointestinal system, the nervous system, and mucous membranes

Culture and isolation on Sabouraud’s agar or BHI with 5% sheep RBC.

What is the gold standard for diagnosing sporotrichosis?

Asteroid bodies
Splendore-Hoeppli phenomenon

Ag-Ab complexes seen in tissue biopsies stained with PAS/GMS.

Cutaneous: Oral potassium iodide
Systemic: Amphotericin B, itraconazole, fluconazole
Surgery in severe cases

What are the treatments for sporotrichosis?

Rabies virus, Genus: Lyssavirus, Family: Rhabdoviridae

What is the etiologic agent of rabies?

G protein: receptor binding, immune target
M protein: links envelope and nucleocapsid
N protein: protects RNA from nucleases
L & NS proteins: RNA polymerase (transcription)

Name the rabies virus virulence factors.

Via bites/saliva of infected animals (mostly dogs), rarely via aerosol or mucous membrane contact

Describe rabies transmission.

Prodromal phase
Acute neurologic period (Furious or Paralytic)
Coma
Death

What are the stages of rabies in humans?

Negri bodies (cytoplasmic inclusions in brain tissue)

What histologic finding confirms rabies?

Immunofluorescence Antibody Test (IFA)

What is the gold standard diagnostic test for rabies?

Category I: No prophylaxis
Category II: Immediate vaccination
Category III: RIG + Vaccine

What are the categories of rabies exposure and PEP recommendations?

Animal handlers, veterinarians, lab personnel, children in endemic areas.

Who should receive pre-exposure prophylaxis (PrEP)?

Leptospira spp. (helical, motile, Gram-negative spirochete)

What is the causative agent of leptospirosis?

Contact with urine of infected animals or contaminated water/soil.

How is leptospirosis transmitted?

Anicteric: mild, self-limiting
Icteric (Weil’s disease): severe, involves jaundice, renal failure, hemorrhage

Name the two major clinical forms of leptospirosis.

LipL32
LigA/B (Ig-like)
OmpL1
FlaA/B flagella (motility)
LPS and others like HtpG, Loa22

What are the main virulence factors of Leptospira?

Microscopic Agglutination Test (MAT)

What is the gold standard serological test for leptospirosis?

Via mucous membranes, skin abrasions, or even intact skin after water exposure.

How does Leptospira enter the human body?

Paracetamol, ORS
Doxycycline (age >8 yrs)
Hospital management in severe cases

What are the treatments for leptospirosis?

Rodent control
PPE in flood/leisure work
Post-exposure prophylaxis with doxycycline
Vaccine (mainly for animals)

What are prevention strategies for leptospirosis?