Microbiology Tutorial

Spirochetal Infections

The organisms causing human spirochetal diseases of major importance include:

• Treponema. The most important is T. pallidum, but the less common diseases known as pinta and yaws are caused by other Treponema species.

• Leptospira. Leptospirosis is one of the most common zoonotic diseases worldwide.

• Borrelia. Borreliosis occurs in several forms, depending upon the species. B. recurrentis spread by lice causes relapsing fever. B. burgdorferi spread by ticks causes Lyme disease.

Syphilis

T. pallidum infection produces characteristic chancre in primary stage, skin rash in secondary stage, and several possible complications years later in tertiary stage:

• Primary: chancre (a sharply demarcated ulcer) appears in a couple of weeks in 1/3 to 1/2 of patients

• Secondary: mucocutaneous rash appears in a couple of months in a few patients; plasma cell infitrates are characteristic

• Tertiary: systemic complications develop years to decades later in a small minority

  • cardiovascular syphilis - thoracic aortic aneurysms from endaortitis

  • neurosyphilis - tabes dorsalis of spinal cord; dementia

  • gummatous necrosis - scarring leads to syphilitic hepatitis, orchitis, osteomyelitis

• Congenital syphilis: spirochetes can cross the placenta in the third trimester; can cause hydrops fetalis and stillbirht; neonates may have pneumonia alba, osteochondritis, meningovascular infection, extramedullary hematopoiesis

Leptospirosis

Leptospirosis is a bacterial disease of tropical and temperate climes that usually is caused by exposure to water contaminated with the urine of infected animals, particularly rodents, by swallowing contaminated food or water or through skin or mucosal contact, including eyes or nose, or through broken skin. The disease is not spread from person to person. The incubation time is 2 days to 4 weeks. It causes a wide range of symptoms that can include high fever, severe headache, chills, muscle aches, and vomiting.

The most severe form (Weil disease) is not common but may include jaundice, abdominal pain, diarrhea, or a rash. Untreated severe disease may be complicated by renal failure, meningitis, liver failure, and respiratory distress. The illness lasts from a few days to 3 weeks or longer. Without treatment, recovery may take several months. In rare cases death occurs. Leptospirosis is confirmed by microbiologic analysis of a blood or urine sample.

Half of cases in the U.S. occur in Hawai'i. The ancient Hawai'ians had strict rules about use of fresh water sources, since they equated use of some of them with subsequent disease.

Borreliosis

Relapsing fever - Borrelia recurrentis is transmitted by the body louse. (There is a less severe form of this disease caused by B. hermsii spread by ticks.) There is an abrupt onset of the illness 3 to 18 days following exposure. Patients typically have fever, marked tachycardia, headache, non-productive cough, myalgias, arthralgias, and weakness. The organisms circulate in the bloodstream and then invade endothelial cells, producing disseminated intravascular coagulation. The relapses result from genetically programmed shifting of outer surface proteins of the organisms that allows a new clone to avoid destruction by antibodies developed against the original organisms.

More severe disease with liver and spleen involvement can lead to abdominal pain with nausea and vomiting. Untreated patients can have mortality rates from 30 to 70%. Laboratory diagnosis is made by finding the organisms on a peripheral blood smear during an acute febrile episode.

Lyme disease - Borrelia burgdorferi is spread by tick bites and may produce erythema chronicum migrans of skin in primary stage at the original site of the tick bite. It may then proceed to systemic dissemination in the secondary stage, and arthritis in the late tertiary stage. Diagnosis is made via serologic testing.

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