Zoonotic Diseases Quick Review

Pandemics and Disease

Pandemics have occurred throughout history, influenced by trade, urbanization, and disease virulence.
Quarantine originated in the 14th century to protect cities from plague.
Dr. John Snow used geographical data to link a cholera outbreak to tainted water in 19th century London.
Modern responses to pandemics are improving due to better understanding of disease.
Urbanization and increased air travel significantly impact infectious disease spread.

Major Pandemics in History

Antonine Plague (165-180): Believed to be smallpox or measles, 5M deaths.
Plague of Justinian (541-542): Yersinia pestis, 30-50M deaths.
Black Death (1347-1351): Yersinia pestis, 200M deaths.
Spanish Flu (1918-1919): H1N1 virus, 40-50M deaths.
HIV/AIDS (1981-present): Virus, 25-35M deaths.
COVID-19 (2019-Present): Coronavirus, 5.7M+ deaths.

Zoonotic Diseases

Zoonotic diseases transmit from vertebrate animals to humans and vice versa; >60% of human pathogens are zoonotic.
Factors like climate change, urbanization, and trade affect zoonoses emergence and distribution.
The WHO defines zoonosis as any disease transmissible between vertebrate animals and humans.
Zoonoses are a public health concern, causing significant illness and death, mainly impacting livestock workers in low-income countries.
Zoonoses are classified into bacterial, viral, parasitic, fungal, rickettsial, chlamydial, and protozoal types.
Transmission can be direct (e.g., avian influenza) or via vectors (e.g., rabies from animal bites).
Zoonotic diseases are classified into synanthropic and exoanthropic based on their ecosystem.
Sapronoses: diseases caused by pathogens surviving on dead organic material (fungal and bacterial).
Reverse zoonoses: diseases transmitted from humans to animals.

Zoonoses of Domestic Animals

Domestic animals are significant in transmitting diseases to humans.
Transmission occurs through direct contact, ingestion, or inhalation.
Examples: Anthrax (Bacillus anthracis), Tuberculosis (Mycobacterium bovis), Brucellosis (Brucella spp.), Rabies (Rabies virus).
Anthrax: transmitted through contact with infected animals/products; mortality can reach 100% in pulmonary form.
Tuberculosis: transmitted via unpasteurized milk/aerosols; can affect the urogenital system.
Brucellosis: transmitted via unpasteurized milk/products; causes flu-like symptoms.
Rabies: transmitted by animal bites; causes excitation, hallucination, and hydrophobia.

Zoonoses of Pets, Companion Animals, and Birds

Close contact with pets increases zoonoses risk.
Common diseases: Brucellosis, Campylobacteriosis, Chlamydiosis, Cat scratch fever, Rabies, Lyme disease, Tularemia.
Birds can transmit Coxiella burnetii, Salmonella spp., and avian influenza A H5N1.
Transmission occurs through direct or indirect contact.
Cat-scratch disease: caused by Bartonella henselae, transmitted through cat scratches/bites.

Zoonoses of Fish and Aquatic Environments

Fish can harbor zoonotic pathogens, mainly bacteria.
Pathogens originate from the aquatic environment contaminated by human and animal waste.
Transmission occurs through non-hygienic handling or consumption of raw/undercooked products.
Important pathogens: Aeromonas hydrophila, E. coli, Vibrio spp., Mycobacterium marinum, Erysipelothrix rhusiopathiae, Lactococcus garvieae, Nocardia spp.
Mycobacterium marinum causes "fish tank granuloma."
Erysipelothrix rhusiopathiae causes "fish-handler’s disease."
Lactococcus garvieae causes endocarditis, bacteremia, and meningitis.
Nocardia spp. causes nocardiosis, characterized by skin infections and pneumonia.

Zoonoses Associated with Food-Borne Pathogens

Food acts as a medium to transmit zoonotic pathogens; causes diarrheal diseases.
Risk factors: Handling animals without precautions, consuming undercooked animal products.
Common pathogens: Salmonella spp., Campylobacter spp., Shiga toxin-producing Escherichia coli (STEC), and hepatitis E virus.
STEC toxins cause gastrointestinal symptoms and kidney failure; can induce hemolytic uremic syndrome (HUS).

Potential Zoonoses Transmitted by Edible Insects

Edible insects (beetles, caterpillars, ants) increasingly consumed globally.
Health risks: allergies, metabolic steroids, pathogens, and parasites.
Insects can harbor pathogens like Campylobacter spp., Enterobacteriaceae, and act as vectors for Salmonella spp. and E. coli.

Emerging and Re-Emerging Zoonoses

Emerging zoonosis: newly recognized or increased incidence.
Factors: human behavior, habitat, ecology, farm practices, urbanization, deforestation, and climate change.
Examples: Avian influenza, Ebola, MERS, SARS, COVID-19.
SFTS: severe fever with thrombocytopenia syndrome, transmitted by ticks.
MERS: transmitted to humans from camels.

Wild Animals and Re-Emerging Zoonoses

Wild animals are intricately connected with human/domesticated animals, and environmental components.
Globalization, habitat destruction, climatic change, and loss of species and biodiversity disrupts the ecological relations.
Wild animals: reservoirs of pathogens that threaten human/animal health, agriculture, and wildlife.

Zoonotic Coronaviruses

Coronaviruses: enveloped, positive-sense single-stranded RNA viruses.
All seven human coronaviruses are zoonotic, with bats as natural hosts.
SARS-CoV, MERS-CoV, and SARS-CoV-2 (COVID-19) are the most severe.
Transmission occurs through respiratory droplets and fomites.

Neglected Zoonoses

Endemic in the developing world, often under-reported and neglected.
Examples: Rabies, Anthrax, Cysticercosis, Brucellosis, Leishmaniasis.

Impact of Zoonoses

Impacted by prevalence, incidence, morbidity, mortality, and economic loss.
Antibiotic resistance: global health challenge that negatively impacts the treatment of bacterial zoonoses.
Animal deaths or reduced productivity result in massive economic losses.
Various disease hampers with international trade and tourism.

Control of Zoonoses

Requires multi-sectorial approach involving humans, animals, and the environment.
Surveillance can be used to detect early infection; improve human health status, manage disease properly, and minimize morbidity and mortality of humans and animals.
Types of surveillance: Pathogen serological syndrome and risk.
General principals of disease control provides a treatment to a_ected individuals, can vaccination of healthy individuals and animals, restricting animal movement, animal population control, and test and cull
Requires combined and multidisciplinary approaches with e_ective epidemiological, vectrol, vector control, and risk management
Preventable through hygiene awareness vaccination, and medical checkup.
Developed countries aid in supporting the controlling of Zoonoses.

Agent Details: Plague (Yersinia pestis)

Plague is a devastating epidemic disease known from ancient times.
Three global pandemics: Justinian Plague, Black Death, and the last started in China in the 1860s.
Yersinia pestis discovered by A. Yersin in 1894.
Morphology: Small gram-negative rods with bipolar stain ("closed safety pins"), nonmotile, has capsule.
Cultivation: Grows on ordinary nutrient media; optimal temperature: 25-30°C, R-form colonies.
Virulence factors: 72-kb virulence plasmid (pYV), Yop proteins, K-antigen, plasminogen activator, lipopolysaccharide; the structure of lipid part of endotoxin alters in order to stimulates bacteria against phagocytosis
Epidemiology: Zoonotic disease of rodents transmitted to humans via fleabites.
Clinical findings: bubonic, pneumonic, or septicemic forms; may also have cutaneous and intestinal forms; fever with extremely painful bubo.
Laboratory diagnosis: Specimens from blood, sputum, or lymph node aspirates.
Treatment and prophylaxis: Aminoglycoside antibiotics (streptomycin or gentamycin); live EV vaccine and formaldehyde-inactivated vaccine, effectiveness of vaccination is generally moderate.

Agent Details: Anthrax (Bacillus anthracis)

Bacterial origin noted by A. Pollander, K. Davaine, and F. Brauell; first isolated by R. Koch in 1876.
Bacillus genus: soil, water, air, and vegetation; B. anthracis is the principal pathogen.
Morphology: Large gram-positive rods, nonmotile, encapsulated, and arranged in chains (streptobacilli).
Cultivation: Grows well in ordinary media and sheep blood agar at 37°C; colonies resemble the "head of a medusa."
Virulence factors: Exotoxins (PA, EF, LF) and antiphagocytic polypeptide capsule.
Resistance: Spores survive in soil for decades; animal carcasses are highly infectious. As the environmental conditions play a substantial role in preservation and spread of anthrax germs, the infection caused by B. anthracis is referred to as sapronosis.
Epidemiology: Herbivores become infected with anthrax by grazing in pastures; potential source of infection is a vast number of wild and domestic animals.
Clinical findings: Cutaneous, inhalation (Wool-sorter´s disease), or gastrointestinal forms, fever with tachypnea.
Laboratory diagnosis: B. anthracis may be isolated from various samples: cutaneous lesions, respiratory specimens, stool or other gastrointestinal excretions, blood or cerebrospinal fluid.
Treatment and prophylaxis: live (attenuated) vaccine containing spores of non-capsulated B. anthracis vaccine strain and aluminum hydroxide-precipitated protective antigen is used

Agent Details: Brucellosis (Brucellae)

Established by B. Bang in 1896 as contagious abortion of cattle.
Types: B. melitensis (goats/sheep), B. abortus (cattle), B. suis (pigs); predominantly associated with associated with human patholody
Morphology: Small gram-negative ovoid-shaped coccobacteria, no spores or capsules (except capsulated B. melitensis).
Cultivation: Slow growth; special media (liver-extract agar and liver-extract broth) with the optimal temperature of culture is 37°C
Antigenic structure: Brucella melitensis carries predominantly M fraction, whereas Brucella abortus group – A fraction.
Virulence factors: Virulence factors of brucellae remain not well-determined and genome doesn’t harbor genetic pathogenicity islands
Transmission: direct or indirect contact with infected animals as result of contact with infected tissues of animals, via cutaneous, respiratory, or alimentary routes
Clinical findings: The is no specific symptoms, affects tissues, and the onset of illness may be acute or insidious
Laboratory diagnosis: Specimens from patient’s blood and urine (for isolation of the pathogen), serum (for detection of antibodies), milk and dairy products (for detection of brucellae) are examined
Treatment and prophylaxis: various live and inactivated vaccines were introduced into clinical practice

Agent Details: Tularemia (Francisella tularensis)

Causative agent first described by G. McCoy and Ch. Chapin in Californian town Tulare in 1912
Types: F. tularensis subsp. tularensis (type A) and F. tularensis subsp. holarctica (type B)
Morphology: Small pleomorphic gram-negative coccobacterium, no spores or capsule.
Cultivation: Doesn´t grow on ordinary media, special media is cultured on glucose blood agar, chocolate agar or charcoal yeast extract agar, 37°C Small, smooth, gray-white, flat, and shiny colonies is giving after 48 h of incubation
Antigenic structure: contains superficial capsule-like Vi and somatic lipopolysaccharide O antigen for the two major biogroups of Francisella tularensis
Virulence: Virulence factors are not well studied due to the bacteria can infect humans by intact skin
Transmission: Numerous rodent species, transmitted via direct animal contact or via insect bites
Clinical findings: Depend on the site of entry (cutaneous, inhalation, or ingestion) with the symptoms high fever with acute onset accompanied with chills
Laboratory diagnosis: Diagnostic, but francisella should be cultured only in biological safety cabinet of BSL-2 level maintaining all personal safety measures
Treatment and prophylaxis: the individuals of high risk (e.g., laboratory personnel) are immunized with live attenuated vaccine of F. tularensis created by N. Gaisky and B. Elbert.