Diseases Of The Cardiovascular System

Introduction

The heart, blood, and blood vessels make up the cardiovascular system.

Lymph, lymph vessels, lymph nodes and lymphoid organs constitute the lymphatic system.

Structure and Function of the Cardiovascular and Lymphatic Systems

The heart circulates substances to and from tissue cells.

Blood is a mixture of plasma and cells.

Plasma transports dissolved substances. Red blood cells carry oxygen. White blood cells are involved in the body’s defense against infection.

Fluid that filters out of capillaries into spaces between tissue cells is called interstitial fluid.

Interstitial fluid enters lymph capillaries and is called lymph; vessels called lymphatics return lymph to the blood.

Lymph nodes contain fixed macrophages, B cells, and T cells.

Bacterial Diseases of the Cardiovascular and Lymphatic Systems

Sepsis and Septic Shock

The growth of microorganisms in blood is called sepsis. Signs include lymphangitis (inflamed lymph vessels).

Sepsis usually results from a focus of infection in the body.

Gram-negative sepsis can lead to septic shock, characterized by decreased blood pressure. Endotoxin causes the symptoms.

Antibiotic-resistant enterococci and group B streptococci cause gram-positive sepsis.

Puerperal sepsis begins as a focal infection of the uterus following childbirth or abortion; it can progress to peritonitis or septicemia.

Streptococcus pyogenes is the most frequent cause.

Oliver Wendell Holmes and Ignaz Semmelweiss demonstrated that puerperal sepsis was transmitted by the hands and instruments of midwives and physicians.

Puerperal sepsis is now uncommon because of modern hygienic techniques and antibiotics.

Bacterial Infections of the Heart

The inner layer of the heart is the endocardium.

Subacute bacterial endocarditis is usually caused by alpha-hemolytic streptococci, staphylococci, or enterococci.

The infection arises from a focus of infection, such as a tooth extraction.

Preexisting heart abnormalities are predisposing factors.

Signs include fever, anemia and heart murmur.

If untreated, the condition is fatal within a few months.

Acute bacterial endocarditis is usually caused by Staphylococcus aureus (or Streptococcus pyogenes).

The bacteria cause rapid destruction of heart valves and is frequently fatal within days or weeks.

Laboratory diagnosis is based on isolation and identification.

Streptococci can also cause pericarditis, inflammation of the pericardium.

Rheumatic Fever

Rheumatic fever is an autoimmune complication of streptococcal infections.

Rheumatic fever is expressed as arthritis or inflammation of the heart. It can result in permanent heart damage.

Antibodies against group A ß-hemolytic streptococci react with streptococcal antigens deposited in joints or heart valves or cross-react with the heart muscle.

Rheumatic fever can follow a streptococcal infection, such as streptococcal sore throat. Streptococci might not be present at the time of rheumatic fever.

Prompt treatment of streptococcal infections can reduce the incidence of rheumatic fever.

Because the organism has remained sensitive to penicillin it is administered as a preventive measure against subsequent streptococcal infections to people who are at risk (people who have had an incidence of rheumatic fever).

Tularemia

Tularemia is caused by Francisella tularensis. The reservoir is small wild mammals, especially rabbits.

Signs include ulceration at the site of entry, followed by septicemia and pneumonia.

Humans contract tularemia by handling diseased carcasses, eating undercooked meat of diseased animals, and being bitten by certain vectors (such as deer flies).

F. tularensis is resistant to phagocytosis.

Laboratory diagnosis is based on an agglutination test on isolated bacteria.

Brucellosis (Undulant Fever)

Brucellosis can be caused by Brucella abortus, B. melitensis, and B. suis.

In the United States, elk and bison constitute the reservoir of B. abortus.

The bacteria enter through minute breaks in the mucosa or skin, reproduced in macrophages, and spread via lymphatics to liver, spleen, or bone marrow.

Signs include malaise and fever that spikes each evening (undulant fever).

Diagnosis is based on serological tests.

Treatment is prolonged because the bacteria are intracellular. Tetracycline and streptomycin are used in combination.

Anthrax

Bacillus anthracis causes anthrax. In soil, endospores can survive for up to 60 years.

Grazing animals acquire an infection after ingesting the endospores.

Humans contract anthrax by handling hides from infected animals. The bacteria enter through cuts in the skin or through the respiratory tract.

Entry through the skins causes cutaneous anthrax and results in a pustule that can progress to septicemia. Over 90% of naturally occuring cases in humans are cutaneous.

Entry through the respiratory tract results in inhalational or pulmonary anthrax, the most dangerous form. Endospores inhaled into the lungs have a high probability of entering the bloodstream, where they may proliferate and cause septic shock. This usually kills the patient within 24 - 36 hours (the mortality rate is nearly 100%).

Gastrointestinal anthrax is caused by ingestion of undercooked food containing the spores. This form is fairly rare but usually has a mortality rate of greater than 50%.

Diagnosis is based on isolation and identification of the bacteria.

Treatment is with ciprofloxacin or doxycycline.

Gangrene

Soft tissue death from ischemia (loss of blood supply) is called gangrene.

Microorganisms grow on nutrients released from gangrenous cells.

Gangrene is especially susceptible to the growth of anaerobic bacteria such as Clostridium perfringens, the causative agent of gas gangrene.

C. perfringens can invade the wall of the uterus during improperly performed abortions.

Surgical removal of necrotic tissue, hyperbaric chambers, amputation, and antibiotics are used to treat gas gangrene.

Systemic Disease Caused by Bites and Scratches

Pasteurella multocida, introduced by the bite of a dog or cat, can cause septicemia.

Anaerobic bacteria such as Clostridium, Bacteroides, and Fusobacterium infect deep animal bites.

Cat-scratch disease is caused by Bartonella henselae.

Vector-Transmitted Diseases

Plague

Plague is caused by Yersinia pestis. The vector is usually the rat flea (Xenopsylla cheopis).

Reservoirs for plague include European rats and North American rodents.

Signs of bubonic plague include bruises on the skin and enlarged lymph nodes (buboes).

The bacteria can enter the lungs via blood and cause pneumonic plague. Pneumonic plague is easily spread by airborne droplets from humans or animals.

Laboratory diagnosis is based on isolation and identification of the bacteria.

Antibiotics are effective in treating plague, but they must be administered promptly after exposure to the disease. Prevention is accomplished by controlling rat populations.

Relapsing Fever

Relapsing fever is caused by Borrelia species and transmitted by soft ticks (Ornithodoros).

The reservoir of the disease is rodents.

Signs include fever, jaundice, and rose-colored spots. Signs recur three or four times after apparent recovery,

Laboratory diagnosis is based on the presence of spirochetes in the patient’s blood,

Lyme Disease (Lyme Borreliosis)

Lyme disease is caused by Borrelia burgdorferi and is transmitted by a tick (Ixodes).

Lyme disease is prevalent on the U.S. Atlantic Coast.

Field mice provide the animal reservoir.

Early symptoms are rash at the bite site and flu-like symptoms. Later signs are irregular heartbeat, neurological signs, and arthritis.

Diagnosis is based on serological tests and clinical symptoms.

Antibiotics are effective when administered early in the disease. Later stages require large amounts of intravenous antibiotics.

Ehrlichiosis

Human ehrlichiosis (Human granulocityc - HGE, and human monocytic - HME) is caused by Ehrlichia species and transmitted by Ixodes ticks.

Typhus

Typhus is caused by rickettsias, obligate intracellular parasites of eukaryotic cells.

Epidemic Typhus

The human body louse Pediculus humanus corporis transmits Rickettsia prowazekii in its feces, which are deposited while the louse is feeding.

Epidemic typhus is prevalent in crowded and unsanitary living conditions that allow the proliferation of lice.

The signs of typhus are rash, prolonged high fever, and stupor.

Tetracyclines and chloramphenicol are used in treatment.

Endemic Murine Typhus

Endemic murine typhus is a less severe disease caused by Rickettsia typhi and transmitted from rodents to humans by the rat flea.

Spotted Fevers

Rickettsia rickettsii is a parasite of ticks (Dermacentor spp.) in the southeastern U.S., Appalachia, and the Rocky Mountain states.

The rickettsia may be transmitted to humans, in whom it causes tickborne typhus fever. (The reservoir and the vector are ticks).

Chloramphenicol and tetracyclines effectively treat Rocky Mountain spotted fever, or tickborne typhus.

Serological tests are used for laboratory diagnosis.

Viral Diseases of the Cardiovascular and Lymphatic Systems

Myocarditis

The usual cause is coxsackievirus. The virus infects the respiratory or gastrointestinal tract and spreads to the heart through blood.

Damage to the mycardium results in scar tissue.

Burkitt’s Lymphoma

Epstein-Barr (EB) virus causes Burkitt’s lymphoma and nasopharyngeal carcinoma.

Burkitt’s lymphoma tends to occur in patients whose immune system has been weakened, for example, by malaria or AIDS.

Infectious Mononucleosis

Infectious mononucleosis is caused by the Epstein-Barr virus (EBV).

The virus multiplies in the parotid glands and is present in saliva. It causes the proliferation of atypical lymphocytes with unusual lobed nuclei during acute infection. Infected B-cells produce non-specific antibodies called heterophil antibodies.

Symptoms include fever, sore throat, lethargy, swollen lymph nodes in the neck, and general weakness. The spleen may be enlarged.

The disease is transmitted by the ingestion of saliva from infected individuals.

Diagnosis is made by an indirect fluorescent-antibody technique to detect IgM antibodies against EBV. If heterophil antibodies are lacking the symptoms may be caused by CMV.

Cytomegalovirus (CMV) Cytomegalic Inclusion disease

CMV (HHV-5) causes intranuclear inclusion bodies and cytomegaly of host cells.

CMV is transmitted by saliva and other body fluids.

CMV inclusion disease can be asymptomatic, a mild disease, or progressive and fatal. Immunosuppressed patients may develop pneumonia.

If the virus crosses the placenta, it can cause congenital infection of the fetus, resulting in imparied mental development, neurological damage, and stillbirth.

Classic Viral Hemorrhagic Fevers

Yellow fever is caused by a virus (yellow fever virus). The vector is the mosquito Aedes aegypti.

Signs and symptoms include fever, chills, headache, nausea and jaundice.

Diagnosis is based on the presence of virus-neutralizing antibodies in the host.

No treatment is available, but there is an attenuated, live viral vaccine.

Dengue is caused by a virus (dengue fever virus) and is transmitted by the mosquito Aedes aegypti.

Signs are fever, muscle and joint pain and rash.

Mosquito abatement is necessary to control the disease.

Dengue hemorrhagic fever (DHF) occurs when a person with antibodies is reinfected with the same dengue virus. It is a more serious form of the disease and can cause circulaory failure and shock.

Emerging Viral Hemorrhagic Fevers

Human diseases caused by Marburg, Ebola, and Lassa fever viruses were first noticed in the late 1960’s.

Marburg virus is found in nonhuman primates; Lassa fever viruses are found in rodents.

Rodents are the reservoirs for Argentine and Bolivian hemorrhagic fevers.

Hantavirus pulmonary syndrome is caused by hantavirus. The virus is contracted by inhalation of dried rodent urine.

Protozoan Diseases of the Cardiovascular and Lymphatic Systems

American Trypanosomiasis (Chagas’ Disease)

Trypanosoma cruzi causes Chagas’ disease. The reservoir includes many wild animals. The vector is reduviid, the “kissing bug.”

Xenodiagnosis allows for the identification of trypanosomes in the intestinal tract of the reduviid bug, which confirms the diagnosis.

Toxoplasmosis

Toxoplasmosis is caused by the sporozoan Toxoplasma gondii.

T. gondii undergoes sexual reproduction in the intestinal tract of domestic cats (the reservoir), and oocysts are eliminated in cat feces.

In the host cell, sporozoites reproduce to form either tissue invading tachyzoites or bradyzoites.

Humans contract the infection by ingesting tachyzoites or tissue cysts in undercooked meat from an infected animal or contact with cat feces (transmission is gastrointestinal).

Congenital infections can occur. Signs and symptoms include severe brain damage or vision problems.

Toxoplasmosis can be identified by serological tests, but interpretation of the results is uncertain.

Malaria

The signs and symptoms of malaria are chills, fever, vomiting, and headache, which occur at intervals of 2-3 days.

Malaria is transmitted by Anopheles mosquitoes. The causative agent is any one of four species of Plasmodium.

Sporozoites reproduced in the liver and release merozoites into the blood stream, where they infect red blood cells and produce more merozoites.

Laboratory diagnosis is based on microscopic observation of merozoites in red blood cells.

New drugs are being developed as the protozoa develop resistance to drugs such as chloroquine.

Leishmaniasis

Leishmania spp., which are transmitted by sandflies, cause leishmaniasis.

The protozoa reproduce in the liver, spleen and kidneys.

Antimony compounds are used for treatment.

Babesiosis

Babesiosis is caused by the protozoan Babesia microti and transmitted to humans by ticks.

Helminthic Diseases of the Cardiovascular and Lymphatic Systems

Schistosomiasis

Species of the blood fluke Schistosoma cause schistosomiasis.

Eggs eliminated with feces hatch into larvae that infect the intermediate host, a snail. Free-swimming cercariae are released from the snail and penetrate the skin of a human.

The adult flukes live in the veins of the liver or urinary bladder in humans.

Granulomas are from the host’s defense to eggs that remain in the body.

Observation of eggs or flukes in feces, skin tests, or indirect serological tests may be used for diagnosis.

Chemotherapy (praziquantel or oxamniquine) is used to treat the disease; sanitation and snail eradication are used to prevent it.

Swimmer’s Itch

Swimmer’s itch is a cutaneous allergic reaction to cercariae that penetrate the skin. The definitive hosts for this fluke are wildfowl.