Lecture 23 - Zoonotic Infections

Zoonotic Infections

Zoonosis = disease of animals transmitted to man

transmission may occur in several ways:• direct contact with diseased flesh - eg., tularemia• drinking raw or unpasteurized cow’s or goat’s milk - eg., tuberculosis• inhalation of dust particles contaminated with animal excreta or

products - eg., psittacosis• eating insufficiently cooked infected flesh - eg., trichinosis• bite of insect vectors carrying infectious agents - eg., plague• bite of diseased animal - eg., rabies

because of their proximity to humans, domestic animals are the morecommon source of zoonoses (domestic animals may become infected bycontact with wild animals or their insect vectors)

occupational risk for some professions - farmers, veterinarians, etc

Zoonotic Infections

Methods of control for diseases in domestic animals that aretransmissible to humans:

• sacrifice or isolation of diseased and/or infected animals• pasteurization of milk• adequate cooking of meat before eating• vector control• vaccination of susceptible animals

Diagnosis requires either isolation of organisms or appropriate serology;pt history and clinical signs may be helpful but not sufficient to make diagnosis

Yersinia pestis - plagueYersinia enterocolitis - enterocolitisYersinia pseudotuberculosis -

appendicitis-like syndrome

Francisella tularensis - ulceroglandular,typhoidal or oculoglandular disease

Brucella melitensisBrucella suisBrucella abortus

Pasteurella multocida - bipolar staining

Facultativeintracellularpathogens;persist inmacrophages:CMI important

Extracellularpathogen;humoral responseimportant

bipolar staining

undulant fever

4 Zoonotic Gram-negative coccobacilli

Yersinia• belongs to Enterobacteriaceae - gram negative rods, which fermentglucose and are oxidase negative• 3 species are pathogenic to man

Yersinia pestis = cause of plague

Y. enterocolitica and Y. pseudotuberculosis = cause entercolitis (alsoknown as yersiniosis)

Yersinia are small gram-negative coccobacilli which often demonstratebi-polar staining (safety-pin) using Giemsa or Wayson stainsY. pestis = non-motileY. enterocolitica and Y. pseudotuberculosis = motile at 25oC but not 37oC

Yersinia pestis = the plague bacillus

1. Epidemiology

- infectious bacteria maintained in nature in sylvatic cycle

- involves rodents & rat flea (Xenopsylla cheopis)- involves ground squirrels in West, prairie dogs

in the Southwest,and wood rats in South

- urban plague begins when infected fleas of the sylvatic cycle infect animals living closer

to humans, such as the rat- starts an urban cycle which increases risk

to man

Genetic location and expression of virulence factors in Yersinia pestis.

Yersinia pestis = the plague bacillus

2. Antigenic structure

- some of the major antigens are expressed on plasmids, while some onchromosome

- F-1 antigen = capsule, antiphagocytic, expressed best at 37oC - V-W antigens and several Yersinia proteins (Yops) are plasmid

gene products coordinately expressed at 37oC in the presence of low Ca2+ concentrations; imp in resisting phagocytosis (V-W) as wellas intracellular survival and growth within macrophages; Yops proteins form a type III secretion system for injecting severalYops proteins into eukaryotic cells which kills them

- coagulase = clots blood in insect gut - LPS = may cause hemorrhage, vascular collapse and focal necrosis - Pla gene = plasminogen activator which degrades fibrin clots and

C3b and C5a

Yersinia pestis = the plague bacillus3. Clinical manifestations

- Y. pestis causes human plague when bacteria are introduced into bodyby bite of infected flea. Rat fleas acquire organism during a blood meal on an infected rodent (usually the rat)

- Y. pestis produces a coagulase which, at <27oC and with help of anenzyme in flea’s gut, clots the blood; this prevents flea from

getting nourishment during the next feeding - regurgitates thebacteria into bite site

Bubonic plague = spread of bacteria to regional lymph nodes (groin oraxillae) forming buboes (swollen, tender lymph nodes) which maysuppurate and drain; bacteria are found within macrophages innodes; septic shock with fatality rate is 75% if untreated

Pneumonic plague = spread to lung can result in respiratory diseaseand aerosol dissemination; death due to respiratory failure(“Black Death”); ~100% fatal if not treated

Pathogenesis of Yersinia pestis in plague patients.

Plague: enlarged, tender inguinal lymph nodes in a Vietnamese childwith bubonic plague.

Plague: advanced stage of inguinal lymphadenitis in bubonic plague. Thenodes have undergone suppuration and the lesion has drained spontaneously.

Smear of lymph node aspirate from a case of bubonic plague showing manybi-polar staining Y. pestis (left, Wayson’s stain). Smear of peripheral blood of patient with septicemic plague, showing bi-polar staining Y. pestis (right, van Gieson stain).

Yersinia pestis = the plague bacillus4. Host defenses

- production of specific anti-Fraction 1 antibodies will stimulate phagocytosis and promote killing by neutrophils

- cell-mediated immunity will activate macrophages and assist inkilling facultative intracellular bacteria

5. Diagnosis

- need to isolate the causative agent - biopsy the bubo and culture

6. Treatment

- streptomycin, tetracycline or chloramphenicol

7. Prevention and control

- formalin-inactivated vaccine available for those travelling to endemicareas and those in high risk groups (only effective against bubonicplague)

Yersinia enterocolitica

• common cause of enterocolitis• rodents, dogs, cats and domestic farm animals are natural hosts• ingestion of contaminated food or water, bacteria have affinity for M

cells in Peyer’s patches, traverse the mucosal membranes of gitract thru M cells, then grow in mesenteric lymph nodes

• facultative intracellular bacteria• have many of the same genes of Y. pestis as well as invasin gene (inv)

and ail (adherence invasion locus)• enterocolitis = abdominal pain, diarrhea and fever; regional lymph-

adenopathy; watery diarrhea due to heat-stable enterotoxinwhich stimulates cGMP

• often self-limited; fluid and electrolytes if needed; TMP-SMZ andaminoglycosides if liver and spleen abscesses occur

Yersinia pseudotuberculosis

• causes an appendicitis-like syndrome• ingestion of contaminated food or water, bacteria have affinity for M

cells in Peyer’s patches, traverse the mucosal membranes of gitract thru M cells, then grow in mesenteric lymph nodes

• facultative intracellular bacteria• have many of the same genes of Y. pestis as well as invasin gene (inv)

and ail (adherence invasion locus)• abdominal pain, regional lymphadenopathy; usually no diarrhea; symptoms

of appendicitis• TMP-SMZ, aminoglycosides, cephalosporins, and other drugs have been

used

Francisella

• non-motile gram-negative coccobacilli• encapsulated

• F. tularensis causes tularemia or rabbit fever - spread to man directlyby ticks and deerflies; most strains which infects rabbits arehighly infectious to humans (could result from skinning rabbit, oreating infected rabbit meat, or bite of infected tick or deerfly)

• facultative intracellular pathogens in macrophages and monocytes

FrancisellaClinical manifestations: - after 2-5 d incubation, organisms are multiplying in cells of RES,forming focal necrosis and small granulomas; signs and symptoms dependon how disease contracted:

1. Ulceroglandular = most common; bacteria penetrates skin abrasion, produces local lesion which necrotizes and spreads to local lymphnodes with regional lymphadenopathy; could also be from tick bite

2. Typhoidal = after ingestion of contaminated meat, severe typhoid-likedisease occurs, with local abscesses in Peyer’s patches and mesenteric lymph nodes; high fever and severe toxemia noted

3. Oculogladular = infection via conjunctival membrane leads to swellingof eyelid, ulceration of conjunctiva and regional lymphadenopathy

Tularaemia: irregular ulcerat the site of the initiallesion.

Protection against Francisella tularensis or Yersinia pestis is cell-mediated.

FrancisellaDiagnosis = direct immunofluorescent antibody staining of bacteria in

infected tissues or blood; isolation and culture is dangerous forlab; serologic demonstration of rising antibody also used andis most common test used

Treatment = streptomycin or gentamicin

Control = live attenuated vaccine used for lab workers; protectivegloves and goggles for hunters and trappers

Pasteurella

1. Characteristics- small gram-negative coccobacillus- bi-polar staining- encapsulated (A, B, D and E types; A most common)- most common strain is Pasteurella multocida

2. Epidemiology- rabbits, cats and dogs carry these bacteria as normal flora of naso- pharynx and gingival crevices- cattle which carry these strains may develop fulminating hemorrhagic pneumonia when stressed or dehydrated (shipping fever); also been seen in flocks of chickens and turkeys- rabbits gets snuffles (chronic nasopharyngeal infection)

Pasteurella

3. Pathogenesis- extracellular pathogens which resist phagocytosis due to capsule- LPS may contribute to tissue damage- pilus serves as adhesin- after entry thru skin due to animal bite, local colonization is

mediated thru pilus at wound site, with spread to regionallymph nodes; acute inflammatory response follows butbacteria resist ingestion due to capsule

4. Clinical manifestations- P. multocida typically is seen in infected cat and dog bites, with

localized inflammation at the site with abscess formation andregional lymphadenopathy; osteomyelitis is a seriouscomplication of this disease

Protection against Pasteurella multocida is mediated by opsonic antibodies.

Pasteurella

Diagnosis: should suspect this organism in any infected cat or dog bite;isolate organism from abscess and culture

Treatment: penicillin, tetracycline or chloramphenicol used to treatabscesses; prolonged treatment needed; abscess should bedrained

Control: no effective vaccine available; ampicillin can be usedprophylactically

BrucellaImp cause of disease of cattle, goats, pigs, etc. usually affecting theirreproductive organs leading to abortion, sterility and decreased milkproduction. Humans infected thru contact with diseased animals, causean acute febrile disease (undulant fever) or a more chronic processwhich may have wide array of symptoms

Characteristics:- gram-negative coccobacillus, no capsule- slow growers, aerobic, catalase and oxidase positive

B. melitensis = goats and sheepB. abortus = cattleB. suis = pigsB. canis = dogs (infrequent cause of human infections)

Important source of disease for humans

Brucella

Predilection of brucellae for reproductive organs of ruminants due to presence of erythritol in amniotic and allantoic fluid - leads to abortion shedding huge numbers of bacteria; bacteria also establish themselvesin mammary glands, infecting milk (animals usually show no symptoms).

Humans become infected by handling these animals or drinking contaminatedmilk.

Brucellosis is relatively uncommon in US (150-200 cases/yr due to animalvaccination) but endemic in many parts of world

Sources of Brucella infection.

BrucellaPathogenesis:- brucellae gain entrance thru broken skin, by ingestion or thru conjunctiva;carried to liver, spleen and bone marrow by lymphatics; are facultativeintracellular pathogens multiplying in RES- intracellular multiplication induces chronic inflammatory response char.by tissue lesions with minute granulomas composed of epitheliod cells,PMNs, lymphocytes and some giant cells, usu. in spleen and bone marrow

Clinical manifestations:- 2-4 wk incubation- onset is influenza-like, with fever, severe arm and muscle pain, sweatingand fatigue; disease may continue for weeks with fever and symptomsrising and falling in 10 d intervals (undulant fever) - most pts recoverin 3-12 months- some pts develop chronic infections with arthritis, meningitis, etc.- abortion is not seen in humans

BrucellaHost defenses: CMI is most important

Diagnosis: isolation from blood, lymph nodes and bone marrow aspirates;requires special media; serological results are often only test whichmakes diagnosis

Prevention/control: live attenuated vaccines for animals; pasteurize milk;animals which are infected should be sacrificed to protect herd

Treatment: combination of doxycycline and rifampin, doxycyline and gentamicin, or TMP-SMZ for pregnant women and children

“LEPTOSPIRA”

Leptospirosis (or Weil’s disease) is a zoonosis caused by pathogenic species of leptospira, Leptospira interrogans. Saprophytic strains are called L. biflexa.

Characteristics:

• Tightly coiled aerobic spirochete

• -oxidation of fatty acids

• can be grown in medium with rabbit serum (Fletcher’s medium)

Leptospira interrogans serotype icterohaemorrhagiae. Silver staining of organisms grown in culture. Notice the tightly coiled body with hooked ends.

Darkfield microscopy of Leptospira.

LeptospiraPathogenesis:- zoonosis of rats, dogs, cats, horses, cattle and pigs- animals which develop carrier state shed leptospira in urine (even

immunized dogs might shed organisms)- leptospires colonize kidney tubules of animals to produce a chronic

carrier state- man becomes infected with contact with urine-contaminated soil

and water (often swimming or ingestion of contaminated foodor water)

- leptospires enter thru mucous membranes or skin abrasions, thenspreads thru blood to all tissues

- tissue damage is to endothelium of small vessels - mech unknownno LPS or toxins

- greatest risk of infection is to those whose occupation brings themin most contact with animals

Stages of icteric and anicteric leptospirosis.

Leptospira

Clinical manifestations:- biphasic disease with involvement of the CNS, kdiney and liver

- 5-13% of aseptic meningitis due to leptsopires

- Weil’s syndrome = severe form of leptospirosis characterized byjaundice, renal damage and interstitial nephritis

Leptospira

Immunity: humoral antibody response is needed for host defense

Diagnosis: serology more common than isolation and culture; a microscopicagglutination test is done using pool of leptospiral antigens and ptserum and agglutination determined by microscopy- can isolate or detect leptospira in blood or CSF early indisease, while later, most leptospires are present in urine

Treatment: penicillin or doxycycline is effective if given during 1stphase of disease; animal vaccine is used for most animals atrisk of infection