Zoonoses: an Epidemiologic Perspective: Zoonoses: an Epidemiologic Perspective Dr. Lynora Saxinger
‘ID’ ologist
April 5, 2006
Objectives: Objectives Review definition of zoonotic disease
Using representative examples, discuss
Factors affecting transmission
Geographic/environmental influences
Learn about the epidemiology of the following examples of zoonotic disease
Echinococcosis
Leptospirosis
Brucellosis
Lyme disease
Resources: Resources Chapter 314 – Mandell “Principles and Practice of Infectious Diseases”
Disease specific chapters in Mandell
Chapter 12 (Pg 301), Nelson text
Emerging and New Infectious Diseases
EMERGING INFECTIOUS DISEASES (Journal)
http://www.cdc.gov/ncidod/eid/
Zoonotic Infections in Travellers to the Tropics Prim Care Clin Off Pract 29(4), Dec 2002
Strickland – Tropical Medicine, 8th Ed. Chapter 135 pg 979 “Zoonoses”
Definitions: Definitions An epizootic an epidemic in a population of wild animals
A vector is a living organism that carries a disease-causing organism to new hosts
A definitive host is the host in which parasites go through their sexual stage
The intermediate host can harbor the parasite but it cannot undergo sexual reproduction
The reservoir host is the host that a pathogen normally resides in
ZOONOSES: DEFINITION: ZOONOSES: DEFINITION Complex group of diseases caused by diverse microorganisms that usually reside in / cause disease in ANIMALS
Characteristics of these diseases:
NONHUMAN VERTEBRATE RESERVOIR
TRANSMISSION TO PEOPLE
direct by airborne exposure, contact, ingestion of animal products (orthozoonoses)
May require more than one vertebrate host (cyclozoonoses)
invertebrate intermediate (metazoonoses)
nonanimal sites and reservoirs and vertebrates in cycle (saprozoonoses)
Cause a recognized CLINICAL SYNDROME
infected persons develop disease
Zoonoses:: Zoonoses: > 200 zoonotic pathogens
include the largest parasites (macrohelminths) to the smallest pathogens (prions, viruses)
Prions (bovine spongioform encephalopathy)
Viruses (Dengue, Hanta, West Nile, rabies)
Bacteria (Brucellosis, Leptospirosis, Q fever, Plague)
Protozoans (Babesiosis, Chagas disease)
Helminths (trichinosis, echinococcosis)
Worldwide importance
historical (rabies, bubonic plague, typhus)
contemporary (Lyme disease, BSE)
Most important infections historically were acquired from animals, those that required a human reservoir only became possible only after populations reached a critical size
People, Animals, Bugs: People, Animals, Bugs
Zoonoses- Where, Why, How?: Zoonoses- Where, Why, How? Global distribution
Exotic locales- adventure tourism
Domestic and laboratory animal contacts
Pets
Have economic and political implications- e.g. emergence of BSE in UK, threatened emergence in Canada and implications for trade,
Factors Influencing the Epidemiology of Zoonoses: Factors Influencing the Epidemiology of Zoonoses Largely dependent on factors influencing animal and vector populations- intermediate hosts allow persistence even when human population is minimal
Type and risk of human encounters with vector and reservoirs affects infection risk: finding “new” diseases
Humans often dead end hosts- limited interspecies transmission and often limited infectivity among humans (except pneumonic plague, yellow fever)
Factors Influencing the Epidemiology of Zoonoses: Factors Influencing the Epidemiology of Zoonoses Geography and Human Activities
LYME DISEASE – regrowth of forest in NE US with ↑deer and tick populations- recognized in 1970s, and reportable since 1991: 10-15 000 cases/year
RABIES – Importation of infected raccoons to West Virginian hunting camps in 1978- started a rabies epizootic to Middle Atlantic, NE US states and Ontario (racoons, skunks, cats, rabbits…)
Rabies Cases: Rabies Cases 1969-99
Factors Influencing the Epidemiology of Zoonoses: Factors Influencing the Epidemiology of Zoonoses Travel- distribution of zoonotic diseases impact immunization choices, medications, food and drink advice…
Military Actions – movement of large numbers of suceptible soldiers into endemic areas ↑ awareness of diseases
Korean Hemorrhagic Fever (UN troops)
Q fever after Desert Storm
Cutaneous leishmaniasis- Sinai Desert
Crimean War- First description brucellosis- Marston
Factors Influencing the Epidemiology of Zoonoses: Factors Influencing the Epidemiology of Zoonoses CLIMATE
Temperature, soil, moisture conditions
Temperature affects arthropod vectors, vegetation, and animal migration
Anthrax spores: disease more likely if warm “incubator” soil conditions met
Ticks transmitting Lyme and RMSF – not found in colder, Northern climate
Leptospirosis and rain
Factors Influencing the Epidemiology of Zoonoses: Factors Influencing the Epidemiology of Zoonoses Animal, Avian, Aquatic HOSTS
Host Susceptibility (genetic, natural and acquired immunity) influences spread
Rabies vaccination of dogs in developed world has almost eliminated disease
Domestic animals may acquire tularemia, plague, rabies, or carry infected ticks
Migrating birds can carry arboviruses
Aquatic mammals can act as sources for Giardia lamblia (waterborne) or tularemia (contact)
Factors Influencing the Epidemiology of Zoonoses: Factors Influencing the Epidemiology of Zoonoses MIGRATION
Animal reservoir movement, co-hosts that allow long term survival, overwintering birds, migratory patterns
Tularemia: migrating Canadian muskrats in Vermont
RMSF in the Bronx (?? Bird dropped tick)
Factors Influencing the Epidemiology of Zoonoses: Factors Influencing the Epidemiology of Zoonoses ARTHROPODS
Pathogens ability to perpetuate in an arthropod host = vectorial capacity
conditions affecting multiplication of arthropod and vertebrate host
Lyme- deer, ticks, acorns, gypsy moths
Asian tiger mosquito from used tire casings imported / stockpiled in Texas- vector for 22 arboviruses, spread to 25 states
Convergence of Factors: Convergence of Factors These factors may affect more than one disease: Malaysia has had outbreaks of the following in the last few years
Leptospirosis
enterovirus 71 encephalitis
Chikungunya polyarthritis
Nipah encephalitis
Example of a Zoonosis: Echinococcosis: Example of a Zoonosis: Echinococcosis Life cycle
Epidemiology
Caused by a dog tapeworm…: Caused by a dog tapeworm… Affects many mammalian species
Definitive host- canine carnivores, who pass infected eggs in their feces
Intermediate hosts- pastoral: farm animals (sheep, cattle, swine, horses)
Eat eggs with soil or vegetation→ hatches, →penetrates intestinal wall → lodges in viscera or lungs→ develops cysts→viscera eaten by canid…
Humans usually incidental hosts but may be intermediate
People and herding dogs: People and herding dogs
Slide21: Transmission: Egg ingestion
(viable for days-years) Canine: wild or domestic
Feces contaminate soil Sheep, caribou or moose (people): infected by grazing Hydatid cysts in viscera of
intermediate host Canine eats contaminated entrails: adult form – eggs in feces
Echinococcus granulosus and Hydatid Disease (cont’d): Echinococcus granulosus and Hydatid Disease (cont’d) Distribution
S. America
Mediterranean
South Central Russia
Central Asia
Australia
Africa Distribution: Echinococcus granulosus
Echinococcus granulosus and Hydatid Disease (cont’d): Echinococcus granulosus and Hydatid Disease (cont’d) World: Prevalence
150 cysts/100,000 population in Uruguay & Argentina (CXR)
6-9% Peru/Andes (CXR +/- serology)
Animals: 32% dogs, 89% sheep
2% Libya
Hyperendemic area: Turkana/Kenya
198 cases/100,000 (surgical disease)
Epidemiology of Transmission: Epidemiology of Transmission Risk- proportional to how closely humans live with their dogs
Turkana- sleep with dogs, dogs lick children clean, dog feces used as cosmetic, burial practices
Beliefs may contribute to transmission
Cysts in animals thought to be for water storage, thus desirable
Giving viscera to dogs to consume after slaughtering
Alberta Data Reference: Somily, Miedzinski, Robinson and Marrie Poster P-785, 42nd ICAAC San Diego: Alberta Data Reference: Somily, Miedzinski, Robinson and Marrie Poster P-785, 42nd ICAAC San Diego Sporadic in Northern Canada and Alaska
sylvatic variant
Chart review of medical records ‘91-’01
N=42
22 definite/probable : 77% F, 50% Canadian
20 possible : 45% F, 70% Canadian born
28 hepatic, 11 pulmonary, 3 other
17/42 cases – First Nations ancestry
Of sylvatic cases: 15 observed, 6 resected, 1 medical therapy, 7 combined therapy : 1 death
Echinococcus granulosus and Hydatid Disease (cont’d) : Echinococcus granulosus and Hydatid Disease (cont’d) Clinical manifestations and pathology
Pressure effects of cysts on an organ/tissue, and unique to organ
Onset: months to years
Organ involvement
Single vs multiple cysts
Location
Liver >Lungs> Other
Cyst rupture - complications
Echinococcus granulosus and Hydatid Disease (cont’d): Echinococcus granulosus and Hydatid Disease (cont’d) Diagnosis by epidemiology…
History of exposure/residence in endemic areas
Mass on physical exam
Radiography
U/S
CT, MR
Fluid aspiration (+/- hydatid sand)
Other Treatment: No impact on transmission, however…: Other Treatment: No impact on transmission, however… Antiparasitic drugs (Albendazole / Mebendazole)
~25-35% recurrence
Surgical removal
up to 30% local recurrence
try to prevent development of disseminated disease post rupture with Rx?
Is the Canadian epidemiology different?: Is the Canadian epidemiology different? Intermediate hosts documented:
reindeer, caribou, moose and elk (not buffalo)
Definitive hosts :
dogs (up to 25% - 50% infected), wolves, coyotes
Northern sylvatic echinococcosis said to have an excellent prognosis
Meltzer,1956 (n=180) and Wilson, 1968 (n=101) and Finlay, 1992 (5 pediatric cases)
Said not to cause anaphylaxis/seeding
Control: Discussion: Control: Discussion Treat the definitive hosts periodically
Praziquantel to dogs
Education
don’t feed raw viscera to dogs, dog feces exposures
Inspection of abattoirs
Viscera handling, canine presence
New Zealand, Tasmania, Cyprus, Argentina, Chile- have had success with control
Leptospirosis: A Worldwide Zoonosis: Leptospirosis: A Worldwide Zoonosis Leptospirosis
zoonotic disease caused by a spirochete
often related to occupation
Humans are infected via contact with
animal reservoirs (many species-e.g. rats, mice, or hedgehogs)
contaminated environment (soil, sewage, or water)
The clinical spectrum of the disease depends on the serogroup and the host
mild flulike illness ranging to severe disease with multiple organ failure (Weil's disease)
An Australian Settlers Diary: 1866: An Australian Settlers Diary: 1866 ? leptospirosis
“I was down last week three days with the fever & had the sandy blight badly at the same time. …the fever is no worse than a very bad bilious attack & sick headache only you have no power to move. It takes you as suddenly as if you were shot & leaves you as weak as a cat... “
Epidemiology of Leptospirosis: Epidemiology of Leptospirosis Leptospirosis occurs worldwide
Infections are endemic in most temperate and tropical climates
peak occurrence during or immediately following periods of high precipitation.
Epidemiology of Leptospirosis: Epidemiology of Leptospirosis Reliable surveillance data lacking
clinical presentation is nonspecific and diagnostic capabilities are usually limited in countries with the greatest burden of disease
Tropics: antibody prevalence rates to local may exceed 80%.
In 1992, Hawaii reported an annual incidence of roughly 128 per 100,000 population using active surveillance.
Many Species Involved: Many Species Involved Leptospirosis is a disease of amphibians, reptiles, and mammals including humans
Wild, domestic, or peridomestic animal infections, such as those occurring in rodents, livestock, and dogs, range from subclinical to symptomatic
Infected animals may become reservoirs
Transmission: Transmission Leptospires are excreted in animal urine become established in soil and water (survive for weeks to months)
Contact with this soil or water- infection
Humans and animals can also become infected by direct contact with infected animal tissues and organs.
Leptospirosis in Humans: Leptospirosis in Humans Occupational risk
animal trappers and hunters, dairy farmers, livestock workers, abattoir workers, veterinarians, rice farmers, military personnel, and sewer workers.
Recreational exposures
wading, swimming, white-water rafting, canoeing, kayaking, and competitive swimming
Disease M > F
related to occupational and recreational activities.
Leptospirosis in Humans: Leptospirosis in Humans Epidemics of leptospirosis have been associated with flooding, tropical storms, and hurricanes
Caribbean and Central and South America.
Heavy rains increase human exposure to leptospire-contaminated groundwater (walking through streams, puddles) and soil
Rains may also facilitate peridomestic rodent infestation
Animal Leptospirosis: Ontario Example: Animal Leptospirosis: Ontario Example Leptospirosis in dogs increased in 2000
The highest frequency of seropositive cases occurred from September to December 2000, with the peak in November
The year 2000 was the warmest in Ontario in the previous decade
Was also the third wettest in the fall period in the last decade
Leptospirosis Control: Leptospirosis Control Educate re: transmission- water exposure
Protective clothes in hazardous work
Drain contaminated waters where possible, or shut the pool!
Rodent control, burn sugarcane fields before harvest
???Immunization- animals, humans
Preventative doxycycline
Brucellosis: A Prototypical Zoonosis: Brucellosis: A Prototypical Zoonosis Undulant Fever, Malta Fever, Mediterranean Fever
Systemic bacterial disease of domestic and wild animals with worldwide distribution
High morbidity in humans-
Fever, weakness, sweats, weight loss, localized infection of liver/spleen, also bone, joint, genitourinary: lasts days- months
Bacteria persistently infect the animal host:
Brucella abortus, Brucella melitensis, Brucella suis
Diagnosed by microbiologic culture and serology
Brucellosis Epidemiology: : Brucellosis Epidemiology: Likely underrecognized/reported
Worldwide, especially Mediterranean Europe, north and east africa, Middle East, India, Central Asia, Mexico, Central and South America
OCCUPATIONAL:
work with animals or tissues: farm workers, butchers, veterinarians
Sporadic cases with consuming unpasteurized milk/products
Brucellosis Epidemiology:: Brucellosis Epidemiology: Eradication/control of bovine
Brucellosis has reduced human
disease in US, except for link with
unpasteurized Mexican goat cheese
Reservoir/Transmission: Reservoir/Transmission Cattle, swine, goats, sheep, yaks, camels, and occasionally elk, bison, caribou, deer
Transmission
Nonintact skin or mucosal contact with infected animal tissues, blood, urine, vaginal discharge, aborted fetuses, placenta (localizes in reproductive tissues)
Ingestion of raw milk/milk products
Airborne infection of penned animals, lab workers
Cultural /Regional differences: Cultural /Regional differences Saudi Arabia : national human seroprevalence 15%
Brucella melitensis clinical disease incidence in humans is close to 40 cases per 100,000
the Kingdom annually imports a few million heads of sheep and goats (for sacrifice during Hajj) from Africa, India, and Australia
uncontrolled importation of animals that are poorly screened: Control program needed
Control: Discussion Points: Control: Discussion Points Considerations:
Education/cultural practices
recruitment and training of qualified veterinarians
development of an adequate number of animal quarantine centers
implementing legislation to control marketing and movement of animals.
Prevention: Prevention Education re: unpasteurized dairy products
Abattoir / slaughterhouse / hunter safety education (ventilation)
Educations re: tissues – aborting animals
Test livestock (ELISA)- segregation or slaughter of infected
Immunize young sheep/goats
PASTEURIZE MILK PRODUCTS!!!!
Trouble from Ticks: Lyme Disease: Trouble from Ticks: Lyme Disease
Lyme Disease: Lyme Disease Caused by tick borne spirochete
Borrelia burgdorferi
Most common vector borne disease in the US
Recognized in 1975 by cluster of cases in Lyme, Conneticut of “juvenile rheumatoid arthritis”….three stage illness
Localized Disseminated Persistent
persistent disease
arthritis, neurologic
system, skin
spread to skin,
heart, joints,
nervous system Characteristic rash
Lyme Epidemiology: Lyme Epidemiology 1-14 >=15* 0 1999
Lyme Epidemiology: Lyme Epidemiology After initial description
Rapid increase in reported cases
Geographic spread across the US
Microenvironments, niches:
remote sensing and geographic information system (RS/GIS) technologies to correlate specific ecologic conditions with outbreaks of infectious diseases
specific vegetation and landscape patterns can be described and predicted by RS/GIS.
Lyme Epidemiology: Canadian Ticks: Lyme Epidemiology: Canadian Ticks In Canada the distribution of I. scapularis is uneven and focal (bird migration plays role)
adult I. scapularis detected in low numbers in southern Manitoba, Ontario, the eastern townships of Quebec, Nova Scotia, New Brunswick, PEI, and Newfoundland
at the present time, reproducing populations of I. scapularis are only known to be established on Lake Erie, Ontario.
Vector (Ixodid ticks ) and Hosts: Vector (Ixodid ticks ) and Hosts Adult ticks feed and mate on large animals, especially deer, in the fall and early spring
Female ticks then lay eggs on the ground and in summer, eggs hatch
Larvae feed on rodents and birds in the summer- fall
inactive until the next spring when they molt into nymphs.
Nymphs feed on small rodents and birds in the late spring and summer and molt into adults in the fall, completing the 2-year life cycle.
Ticks typically become infected with Lyme disease bacteria when they feed on infected small animals, particularly the white-footed mouse
The bacteria remain in the tick, which transmits Lyme disease bacteria to other small rodents, other animals, and humans with subsequent feeds
Lyme Ecology: Lyme Ecology Ticks must attach >24h for disease transmission
Deer not involved in lifecycle of the spirochete but are important for the ticks
West coast: nymphal ticks prefer lizards which do not support infection: lower rates
Ticks feeding on birds may account for geographic spread
Lyme Issues: Lyme Issues Clinical diagnosis of early disease quite good (characteristic skin lesion)
Late Lyme arthritis and encephalopathy can be difficult to distinguish from difficult to clarify syndromes such as fibromyalgia
Dx: clinical picture, EXPOSURE, and serology for antibody response
Antibiotics are effective in the first 2 stages of disease
Control of Lyme Disease: Control of Lyme Disease Prevention:
Public Education re: tick avoidance/removal
Tick control: not practical for large scale
? Deer control
Permethrin cotton balls for mice nesting???
Vaccine: 76-83% effective ?duration
Who to vaccinate??
15-70 y old, outdoor exposures, high prevalence areas
Control of Patient, Contacts, Environment-
Not necessary/feasible
Conclusions: Conclusions Zoonotic diseases are rare (or at least uncommon) individual causes of morbidity and mortality
BUT
contribute very significantly as a group to human disease
Knowing the complex ecology of the hosts, vectors and pathogens is essential in the clinical and epidemiologic understanding of these diseases
Final Word on : Final Word on Google search – first hit is “Daniel Shapiro’s Zoonosis web page”
Gives this definition: “A zoonosis is a disease that humans may acquire from animals. For every cute, cuddly (non-human) creature out there, there is something horrible that you can potentially catch from it.”