Spirochetes

Characteristics of spirochetes

Slender, helically coiled bacteria; motile by endoflagella; stain poorly with Gram stain; inactive biochemically; unstable in environment

How are spirochetes best visualized?

Dark-field microscopy, phase-contrast microscopy, or fluorescence microscopy

Three main genera of spirochetes

Leptospira, Brachyspira, Borrelia

Shape of Leptospira

Slender, coiled spirochetes with hook-shaped ends

Oxygen requirement of Leptospira

Obligate aerobes

How are Leptospira shed?

In urine of infected animals

Where do Leptospira survive in the environment?

Ponds, surface water, and moist soil

How are Leptospira species differentiated?

DNA homology

What is a serovar?

A serologically distinct variant within a species

Example Leptospira serovars

L. interrogans serovar canicola; L. interrogans serovar icterohemorrhagiae

Maintenance hosts of Leptospira

Rodents and small mammals

Leptospira infection in maintenance hosts

Usually subclinical with persistent urinary shedding

Incidental hosts of Leptospira

Develop disease ranging from mild to severe

Main routes of Leptospira transmission

Ingestion of contaminated water; entry through skin or mucosal abrasions

Leptospira serovar associated with cattle

L. borgpetersenii serovar hardjo and L. interrogans serovar hardjo

Leptospira serovar associated with pigs

L. interrogans serovar pomona

Leptospira serovar associated with dogs

L. interrogans serovar canicola

Major reproductive effects of leptospirosis in cattle and sheep

Abortions, stillbirths, agalactia

Major reproductive effect of leptospirosis in horses

Abortions and periodic ophthalmia

Major reproductive effect of leptospirosis in pigs

Abortions, reproductive failure, stillbirths

Clinical signs of leptospirosis in dogs

Renal disease in puppies; chronic disease in adults

younger animals are more severely affected

Why are many ingested Leptospira destroyed?

They are destroyed by gastric acid

How do Leptospira spread after entering the body?

Hematogenous spread

Main organs affected after Leptospira dissemination

Multiple organs, especially kidneys, CNS, and reproductive tract

Kidney lesion caused by Leptospira

Interstitial nephritis

Cause of renal damage in leptospirosis

Immune complex-mediated renal damage

Some Leptospira serovars produce what toxin?

Potent hemolysins

Clinical effects of Leptospira hemolysins

Anemia, icterus, hemoglobinuria

Vascular lesion associated with leptospirosis

Vasculitis causing hemorrhage

Reproductive consequences of Leptospira infection

Fetal death, resorption, abortion, birth of weak offspring

Type of immunity against Leptospira

Antibody-mediated immunity

Common eye finding in canine leptospirosis

Icterus

(Jaundice)

Major pulmonary lesion in canine leptospirosis

Hemorrhage

Liver lesion in canine leptospirosis

Swollen necrotic liver with acute hepatic hemorrhage

Kidney lesions in canine leptospirosis

Hemoglobinuric nephrosis and shrunken fibrotic kidneys

Kidney lesion in bovine leptospirosis

Dark swollen kidneys

Kidney lesion in equine leptospirosis

Interstitial nephritis

(a kidney disorder where the spaces between the tiny tubes (tubules) inside the kidneys become swollen and inflamed)

Direct diagnostic test for leptospirosis in kidneys

Direct fluorescent antibody stain

a lab technique that uses special antibodies attached to glowing dyes (fluorophores) to find and see specific targets like proteins or germs inside cells or tissue samples under a special microscope

Gold-standard serologic test for leptospirosis

Microscopic agglutination test (MAT)

What antigen does MAT use?

Live leptospires

MAT detects what?

Serovar-specific antibodies

Other serologic tests for leptospirosis

ELISA and CFT

Vaccines available for leptospirosis (what species)

Canine and bovine leptospiral vaccines

Human disease caused by Leptospira

Leptospirosis (Weil's disease, Fort Bragg fever, Swineherd's disease)

Human transmission of leptospirosis

Exposure to contaminated water or infected animals

Major clinical signs of human leptospirosis

Fever, anemia, jaundice, meningitis, nephritis

Mortality rate of human leptospirosis

Approximately 10-15%

Largest genus of spirochetes

Borrelia

Oxygen requirement of Borrelia

Microaerophilic

Generation time of Borrelia

≥18 hours

Borrelia are transmitted by what vectors?

Ticks

Borrelia burgdorferi causes what disease?

Lyme disease

Reservoirs of Borrelia burgdorferi

Mice, deer, and ticks

Major organs affected by Lyme disease

Joints, brain, eyes, heart

Mechanism contributing to Lyme arthritis

Immune complex formation

Clinical signs of Lyme disease in dogs

Fever, arthritis, renal, cardiac, and CNS complications

Clinical signs of Lyme disease in horses and cattle

Arthritis, encephalitis, nephritis, hepatitis

Which stage of Ixodes tick most commonly transmits Lyme disease?

Nymph

How long must a tick remain attached to transmit Lyme disease?

At least 36-48 hours

Characteristic skin lesion of Lyme disease in humans

Bull's-eye rash (erythema migrans)

Other human Lyme disease signs

Arthritis, headache, lymphadenopathy; cardiac and neurologic complications

When does IgM appear after Lyme infection?

About 2 weeks post-infection

When does IgG appear after Lyme infection?

≥30 days post-infection

Tests used to diagnose Lyme disease

IFA, ELISA, confirmed by Western blot

Borrelia coriaceae causes what disease?

Epizootic bovine abortion

(An epizootic is a disease outbreak that quickly affects a large number of animals of the same kind in the same place at the same time)

Vector of Borrelia coriaceae

Tick

Ornithodoros coriaceus

Clinical findings of Borrelia coriaceae infection

Asymptomatic cows, late-term abortion, weak calves

Oxygen requirement of Brachyspira

Anaerobic

Habitat of Brachyspira

Intestines of swine

Brachyspira hyodysenteriae causes what disease?

Swine dysentery (bloody scours)

• An intestinal infection that causes severe diarrhea containing blood

Reservoirs of Brachyspira hyodysenteriae

Rodents and carrier swine

Transmission of swine dysentery

Fecal-oral transmission

Major virulence factors of Brachyspira hyodysenteriae

β-hemolysin and cytolysin

Age group most affected by swine dysentery

Weaner and grower pigs

Main site of swine dysentery lesions

Large intestine and rectum

Characteristic lesion of swine dysentery

Mucohemorrhagic enteritis

Chronic lesion of swine dysentery

Diphtheritic inflammation of the colon, cecum, and rectum

Bartonella henselae characteristics

Short Gram-negative aerobic rods; fastidious; slow-growing

Natural reservoir of Bartonella henselae

Healthy cats (oropharynx)

Does Bartonella henselae usually cause disease in cats?

No

Human disease caused by Bartonella henselae

Cat scratch disease

Cat-to-cat transmission of Bartonella henselae is through what

By *Ctenocephalides felis* (cat flea)

Is there direct cat-to-cat transmission of Bartonella henselae?

No

Human transmission of cat scratch disease

Cat bites, scratches, contact with flea feces, or cat saliva

Incubation period of cat scratch disease

1-3 weeks

Clinical signs of cat scratch disease

Papular lesions and chronic lymphadenitis

Is cat scratch disease usually self-limiting?

Yes (resolves on its own without needing specific medical treatment)

Diagnosis of cat scratch disease

History, clinical signs, serology, PCR

Treatment for cat scratch disease

Tetracyclines

Characteristics of Coxiella burnetii

Gram-negative, rickettsia-like, obligate intracellular bacterium producing an endospore-like structure

Environmental resistance of Coxiella burnetii

Resistant to heat, sunlight, and many chemical disinfectants

Human disease caused by Coxiella burnetii

Q fever

Main reservoirs of Coxiella burnetii for humans

Cattle, sheep, and goats

Routes of Coxiella burnetii transmission

Arthropods, inhalation, ingestion

Infection in nonpregnant ruminants

Usually inapparent; organisms shed in urine, feces, milk, and other body fluids

Infection in pregnant ruminants

Massive shedding in placental discharges; sporadic abortions in sheep and goats (rarely cattle)

Main human sources of Q fever

Inhalation of organisms and unpasteurized milk

Pathogenesis of Q fever

Replication in vascular endothelium, respiratory epithelium, serosal epithelium, and renal epithelium causing widespread vasculitis, infarction, and diffuse granulomas

Clinical signs of Q fever in humans

Fever, chills, headache, interstitial pneumonia, endocarditis, hepatitis

Diagnosis of Q fever

ELISA and IFA for C. burnetii antibodies