Cardiovascular and Lymphatic System Infections - Part 3

Infectious Mononucleosis

• lymphatic system disease

• often called “mono” or “the kissing disease”

• can be caused by a number of bacteria or viruses

The vast majority of Mononucleosis (MONO) cases are caused by the _______ virus, a member of the herpesvirus family

Epstein-Barr virus (EBV)

• more than 90% of the world’s population is infected with EBV, but only 10% have symptomatic illness

• infection during teen years is likely to cause disease

• infection before or after is unlikely to cause disease

What is the mode of transmission for Mono?

• direct oral contact and contamination with saliva

Infectious Mono — signs and symptoms:

after a 30- to 50-day incubation period:

• sore throat

• high fever

• cervical lymphadenopathy

• gray-white exudate in the throat

• skin rash

• enlarged spleen and liver

sudden leukocytosis, consisting initially of infected B cells and later T cells

What is a hallmark symptom of Mono?

Fatigue; strong, cell-mediated response is decisive in controlling the disease

Mono — prevention and treatment:

• usual treatments are directed at symptom relief

• hospitalization is rarely needed

• occasionally, a rupture of the spleen necessitates immediate surgery to remove it

• vaccine is currently being tested

Hemorrhagic Fever Diseases:

• a number of agents that infect the blood and lymphatics cause extreme fevers, some of which are accompanied by internal hemorrhaging

• the presence of the virus in the bloodstream causes capillary fragility and disrupts the blood-clotting system, which leads to various degrees of pathology, including death

• all viruses causing hemorrhagic fevers are RNA enveloped viruses

• geographic distribution is dependent on where their natural hosts live

Hemorrhagic Fever Diseases — yellow fever, chikungunya, and dengue fever are all notable for what?

the fact that they are spread by the Aedes genus of mosquito:

• all three diseases are common in South America and Africa

• Chikungunya and dengue fever have now spread to the Americas

Hemorrhagic Fever — Yellow fever virus:

• endemic in Africa and South America

• more frequent in rainy climates

Hemorrhagic Fever — Dengue fever:

• endemic in Southeast Asia and Africa

• epidemics have occurred in South America, Central America, and the Caribbean

Hemorrhagic Fever — Chikungunya:

• endemic in Africa

• arrived in Central America in 2013 and in US and Europe in 2014

• went from zero to over 1.7 million cases in the Americas in 3 years

Hemorrhagic Fever Diseases - Ebola and Marburg fevers:

• endemic to Africa

• capillary fragility is extreme and patients can bleed from their orifices and mucous membranes

What animal is thought to be the natural reservoir of Ebola?

bats

______ epidemic of 2014 was the largest ever

Ebola

• sporadic infections still occur on a small scale

Hemorrhagic Fever — Lassa fever:

• endemic to West Africa

• asymptomatic in 80% of cases

• in others, severe symptoms develop

• reservoir is the multimammate rat

Nonhemorrhagic Fever Diseases

• infectious diseases that result in a syndrome characterized by high fever but without the capillary fragility that leads to hemorrhagic symptoms

• caused by bacteria: Brucellosis, Q fever, Cat-Scratch Disease, Ehrlichiosis, Anaplasmosis, Rocky Mountain Spotted Fever

• caused by protozoan: Babesiosis

Brucellosis:

• aka Malta fever, undulant fever, and Bang’s disease

• causes severe outbreaks of placental infections in livestock (but not human placentas)

• listed as a possible bioterrorism agent

What species of bacteria causes Brucellosis?

those in the genus Brucella

• tiny, aerobic Gram-negative coccobacilli

• B. melitensis, B. abortus, and B. suis can cause disease in humans

Brucellosis — pathogenesis and virulence factors:

• enters through damaged skin or via mucous membranes, or the conjunctiva

• taken up by phagocytic cells

• able to avoid destruction in the phagocytes, it is transported easily through the bloodstream and to various organs

• create focal lesions in the liver, spleen, bone marrow, and kidney

Cardinal manifestation of human brucellosis is a fluctuating pattern of fever:

• origin of the name undulant fever

• up-and-down nature of the fever is related to lipopolysaccharide

Q Fever name arose from what?

• frustration of not being able to identify its cause

• Q stands for “query”

Q Fever — signs and symptoms:

• abrupt onset of fever, chills, head and muscle aches, and occasionally a rash

• disease sometimes complicated by pneumonia in 30% of the cases, hepatitis, and endocarditis

• a quarter of the cases are chronic rather than acute and result in vascular damage and endocarditis-like symptoms

Q fever is caused by Coxiella burnetii:

• very small, pleomorphic gram-negative bacterium

• for a time, it was considered a rickettsia

• harbored by a wide assortment of vertebrates and arthropods, especially ticks, which play an essential role in transmission between animals

• ticks do not transmit the disease to humans; humans acquire infection largely by means of environmental contamination and airborne spread

What people are at highest risk for Q fever?

• farm workers, meat cutters, veterinarians, laboratory technicians, and consumers of raw milk products

Cat-Scratch Disease is caused by what bacterium?

Bartonella henselae:

• small, gram-negative rod

• fastidious but not obligate intracellular parasites, so will grow on blood agar

Cat-Scratch Disease — transmission and epidemiology:

• transmitted among cats by fleas

• pathogen is present in over 40% of cats, especially kittens

• 25,000 cases per year in the US

• 80% of cases are in children 2 to 14 years old

Cat-Scratch Disease — signs and symptoms:

• begin 1 to 2 weeks after being clawed or bitten by a cat

• cluster of small papules at the site of inoculation

• most infections remain localized and resolve within a few weeks

Cat-Scratch Disease — prevention and treatment:

• Azithromycin, erythromycin, and rifampin can be effective therapies

• disease can be prevented by flea control and thorough antiseptic cleansing of a cat bite or scratch

Ehrlichia

a small intracellular bacterium with a strict parasitic existence and association with Ixodes ticks

Ehrlichiosis:

• Ehrlichia bacteria

• signs and symptoms include an acute febrile state resulting in headache, muscle pain, and rigors

• most patients recover rapidly with no lasting effects, but about 5% of older, chronically ill patients can die

• rapid diagnosis is done through PCR tests and indirect fluorescent antibody tests

• it is critical to differentiate or detect coinfection with Lyme disease Borrelia, which is carried by the same tick

• Doxycycline for 7-10 days is generally effective

Anaplasma and Anaplasmosis

a small intracellular bacteria

• shares lifestyle characteristics with Ehrlichia

• causes nearly identical clinical manifestations, but the two bacteria have important differences in geographic distributions and are carried by two different species of ticks

• treatment is also with doxycycline

Babesia

a protozoan that infects red blood cells

Babesiosis:

• produces similar symptoms to Ehrlichia and Anaplasma

• also carried by ticks

• found in the upper Great Lakes region as well as in the northeast US

• often diagnosed via a blood smear; the protozoan is visible inside red blood cells

• combined therapy is recommended

  • either:

    • atovaquone (an antiprotozoal) + azithromycin, or

    • clindamycin + quinine (another antiprotozoal)

Rocky Mountain Spotted Fever (RMSF) was named after what?

→ While named for the region in which it was first detected in US, (Rocky Mountains), the disease occurs infrequently in the western United States

• majority of cases are concentrated in the Southeast and Eastern Seaboard regions

• also occurs in Canada and Central and South America

What bacteria causes Rocky Mountain Spotted Fever (RMSF) and what is it carried by?

Rickettsia rickettsii

• transmitted by hard ticks

  • Wood tick

  • Lone Star tick

  • American dog tick (MC)

RMSF infections occur most frequently in the _____ and _____ when the tick vector is most active

spring and summer

RMSF — signs and symptoms:

• after 2 to 4 days of incubation, symptoms are sustained fever, chills, headache, and muscular pain

• distinctive spotted rash occurs 2 to 4 days after the prodrome:

  • usually appears first on wrists, forearms, and ankles, before spreading

  • early lesions are slightly mottled like measles, but later ones can change shape to look like other rashes

RMSF — severe cases:

• in severe, untreated cases, enlarged lesions become necrotic, predisposing the patient to gangrene of the toes or fingertips

• most grave manifestations are cardiovascular disruption, including hypotension, thrombosis, and hemorrhage

• conditions of restlessness, delirium, convulsions, tremor, and coma are signs of the often overwhelming effects on the central nervous system

• fatalities occur in 20% of untreated cases and 5-10% of treated cases

Chagas Disease

• sometimes called “the American trypanosomiasis” or “the new AIDS of the Americas”

  • long incubation time and very difficult to cure

• causative agent is Trypanosoma cruzi:

  • flagellated protozoan

  • a different trypanosome, T. brucei, causes sleeping sickness of the African continent

Chagas Disease — transmission and epidemiology:

• spread by a group of insects called the triatomines

• can be transmitted vertically:

  • crosses the placenta

  • blood transfusion

• prevalence at 8 million people, 300,000 of whom live in the US:

  • cases acquired by travelers or immigrants

  • US screens all donated blood for this disease

Chagas Disease — signs and symptoms:

• multiply in muscle and blood cells

• blood cells rupture and large numbers of trypanosomes are released into the bloodstream

• Acute phase:

  • mild to severe fever, nausea, and fatigue

  • “Chagoma” appears at the site of the bug bite

  • if the bug bite is close to the eyes, a distinct condition called Romana’s sign, swelling of the eyelids, may appear

• Chronic phase:

  • virtually asymptomatic

  • eventually, trypanosomes are found throughout the body and interrupt the function of the heart, brain, and intestinal tract

Chagas Disease — prevention:

• no vaccine exists for Chagas disease

• pesticides and improved building materials in houses used to minimize the presence of the bug

Chagas Disease — treatment:

• most successful if begun in the acute phase

• drugs are only available through the CDC

• during the chronic phase, symptomatic treatment of cardiac and other problems is indicated

Anthrax

• causes disease in the lungs and the skin

• multiplies in large numbers in the blood

• septicemic anthrax is a possible outcome of all forms of anthrax

• has been known for centuries as a zoonotic disease of herbivorous livestock

Why was anthrax important in the history of medical microbiology?

• Robert Koch used anthrax as a model for developing his postulates in 1877

• Louis Pasteur used the disease to prove the usefulness of vaccination

Anthrax — causative agent:

Bacillus anthracis:

• gram-positive, endospore-forming rod

• it is among the largest of all bacterial pathogens

• block-shaped, angular rods 3 to 5 micrometers long and 1 to 1.2 micrometers wide

• central endospores develop under all growth conditions except in the living body of the host

• primary habitat is the soil; endospores are continuously dispersed by means of dust into water and onto the bodies of plants and animals

Anthrax — transmission and epidemiology:

• facultative parasite that undergoes its cycle of vegetative growth and sporulation in the soil

  • animals become infected while grazing on grass contaminated with endospores

  • pathogen is returned to the soil in animal excrement or carcasses, and sporulates, becoming a long-term reservoir of infection

• majority of natural anthrax cases are reported in livestock from Africa, Asia, and the Middle East

• cases in the US have occurred in textile workers handling imported hair or hide products

• anthrax attacks of 2001 were aimed at two senators and several media outlets

  • 22 people acquired anthrax and 5 people died

Anthrax — body locations:

• anthrax infection can exhibit its primary symptoms in various locations in the body:

  • cutaneous anthrax: skin

  • pulmonary anthrax: lungs

  • ingestion of contaminated food: GI tract

  • anthrax meningitis: central nervous system

• cutaneous and pulmonary forms are the most common

• in all forms, the anthrax bacterium gains access to the bloodstream:

  • death is usually the result of an overwhelming septicemia

Anthrax — signs and symptoms:

• pulmonary anthrax and the accompanying pulmonary edema and hemorrhagic lung symptoms can sometimes be the cause of death:

  • difficult to separate the effects of septicemia from the effects of pulmonary infection

• in addition to symptoms at the site of infection, septicemic anthrax results in:

  • headache, fever, and malaise

  • bleeding in the intestine and from mucous membranes may occur in the late stages of septicemia

Anthrax — pathogenesis and virulence factors:

• polypeptide capsule

• “Tripartite” toxin: a protein complex composed of three separate exotoxins

  • end result of exotoxin action is massive inflammation and initiation of shock

• other virulence factors:

  • Hemolysins

  • other enzymes that damage host membranes

Anthrax — culture and diagnosis:

• diagnosis requires a high index of suspicion:

  • anthrax must be present as a possibility in a clinician’s mind or it is likely not be diagnosed

  • a rare disease, it mimics other diseases that are not so rare

• presumptive diagnosis:

  • culturing of the bacterium on blood agar

  • performing a Gram stain

• samples should be handled by the CDC, for all confirmatory tests: Direct fluorescent antibody testing and phage typing

Anthrax — prevention:

• humans should be vaccinated with the purified toxoid if:

  • they have occupational contact with livestock, or products such as hides or bone

  • they are members of the military (certain circumstances)

• effective vaccination requires five inoculations given over a year, with annual boosters:

  • cumbersome nature of the vaccination has spurred research and development of more manageable vaccines

Anthrax — treatment:

• persons suspected of being exposed to the bacterium are given prophylactic antibiotics, which seem to be effective at preventing disease even after exposure

• recommended treatment for anthrax is:

  • Doxycycline

  • Ciprofloxacin

• antibiotic treatment may worsen symptoms

• treatment of human cases are conducted in consultation with the CDC