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 more common source of zoonoses (domestic animals may become infected by contact 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 are transmissible 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

4 Zoonotic Gram-negative coccobacilli Yersinia pestis - plague Yersinia enterocolitis - enterocolitis Yersinia pseudotuberculosis - appendicitis-like syndrome Francisella tularensis - ulceroglandular, typhoidal or oculoglandular disease Brucella melitensis Brucella suis Brucella abortus Pasteurella multocida - bipolar staining bipolar staining Facultative intracellular pathogens; persist in macrophages: CMI important undulant fever Extracellular pathogen; humoral response important

Yersinia belongs to Enterobacteriaceae - gram negative rods, which ferment glucose and are oxidase negative 3 species are pathogenic to man Yersinia pestis = cause of plague Y. enterocolitica and Y. pseudotuberculosis = cause entercolitis (also known as yersiniosis) Yersinia are small gram-negative coccobacilli which often demonstrate bi-polar staining (safety-pin) using Giemsa or Wayson stains Y. pestis = non-motile Y. 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 on chromosome - 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 well as intracellular survival and growth within macrophages; Yops proteins form a type III secretion system for injecting several Yops 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 bacillus 3. Clinical manifestations - Y. pestis causes human plague when bacteria are introduced into body by 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 an enzyme in flea’s gut, clots the blood; this prevents flea from getting nourishment during the next feeding - regurgitates the bacteria into bite site Bubonic plague = spread of bacteria to regional lymph nodes (groin or axillae) forming buboes (swollen, tender lymph nodes) which may suppurate and drain; bacteria are found within macrophages in nodes; septic shock with fatality rate is 75% if untreated Pneumonic plague = spread to lung can result in respiratory disease and 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 child with bubonic plague.

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

Smear of lymph node aspirate from a case of bubonic plague showing many bi-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 bacillus 4. 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 in killing 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 endemic areas and those in high risk groups (only effective against bubonic plague)

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 gi tract 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 enterotoxin which stimulates cGMP often self-limited; fluid and electrolytes if needed; TMP-SMZ and aminoglycosides 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 gi tract 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 directly by ticks and deerflies; most strains which infects rabbits are highly infectious to humans (could result from skinning rabbit, or eating infected rabbit meat, or bite of infected tick or deerfly) facultative intracellular pathogens in macrophages and monocytes

Francisella Clinical manifestations: - after 2-5 d incubation, organisms are multiplying in cells of RES, forming focal necrosis and small granulomas; signs and symptoms depend on how disease contracted: 1. Ulceroglandular = most common; bacteria penetrates skin abrasion, produces local lesion which necrotizes and spreads to local lymph nodes with regional lymphadenopathy; could also be from tick bite 2. Typhoidal = after ingestion of contaminated meat, severe typhoid-like disease 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 swelling of eyelid, ulceration of conjunctiva and regional lymphadenopathy

Tularaemia: irregular ulcer at the site of the initial lesion.

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

Francisella Diagnosis = direct immunofluorescent antibody staining of bacteria in infected tissues or blood; isolation and culture is dangerous for lab; serologic demonstration of rising antibody also used and is most common test used Treatment = streptomycin or gentamicin Control = live attenuated vaccine used for lab workers; protective gloves 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 regional lymph nodes; acute inflammatory response follows but bacteria 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 and regional lymphadenopathy; osteomyelitis is a serious complication 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 treat abscesses; prolonged treatment needed; abscess should be drained Control: no effective vaccine available; ampicillin can be used prophylactically

Brucella Imp cause of disease of cattle, goats, pigs, etc. usually affecting their reproductive organs leading to abortion, sterility and decreased milk production. Humans infected thru contact with diseased animals, cause an acute febrile disease (undulant fever) or a more chronic process which may have wide array of symptoms Characteristics: - gram-negative coccobacillus, no capsule - slow growers, aerobic, catalase and oxidase positive B. melitensis = goats and sheep B. abortus = cattle B. suis = pigs B. 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 themselves in mammary glands, infecting milk (animals usually show no symptoms). Humans become infected by handling these animals or drinking contaminated milk. Brucellosis is relatively uncommon in US (150-200 cases/yr due to animal vaccination) but endemic in many parts of world

Sources of Brucella infection.

Brucella Pathogenesis: - brucellae gain entrance thru broken skin, by ingestion or thru conjunctiva; carried to liver, spleen and bone marrow by lymphatics; are facultative intracellular 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, sweating and fatigue; disease may continue for weeks with fever and symptoms rising and falling in 10 d intervals (undulant fever) - most pts recover in 3-12 months - some pts develop chronic infections with arthritis, meningitis, etc. - abortion is not seen in humans

Brucella Host defenses: CMI is most important Diagnosis: isolation from blood, lymph nodes and bone marrow aspirates; requires special media; serological results are often only test which makes 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” Tightly coiled aerobic spirochete 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.

Leptospira Pathogenesis: - 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 food or water) - leptospires enter thru mucous membranes or skin abrasions, then spreads thru blood to all tissues - tissue damage is to endothelium of small vessels - mech unknown no LPS or toxins - greatest risk of infection is to those whose occupation brings them in 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 by jaundice, renal damage and interstitial nephritis

Leptospira Immunity: humoral antibody response is needed for host defense Diagnosis: serology more common than isolation and culture; a microscopic agglutination test is done using pool of leptospiral antigens and pt serum and agglutination determined by microscopy - can isolate or detect leptospira in blood or CSF early in disease, while later, most leptospires are present in urine Treatment: penicillin or doxycycline is effective if given during 1st phase of disease; animal vaccine is used for most animals at risk of infection