Infections of the blood and lymphatics:

ADVANCE ORGANIZER
The blood and lymph are sterile. Since these two systems carry materials throughout the body, systemic infection can result when these become infected. Septicemia is the actual growth of bacteria in the blood stream. Bacteremia is the presence of bacteria in the blood.

Viral and protozoan infections of the blood and lymph are serious diseases. Malaria is still the greatest killer of mankind. It kills more than a million people a year. There is great difficulty with viral infections because there are so few ways of treating them.

ANATOMY AND PHYSIOLOGY
The circulatory system blood vascular system includes the heart, which has blood flow both to away from it via arteries, veins and capillaries.
The lymphatic system consists of the lymphatic vessels and lymph nodes. The lymph vessels collect extracellular fluid and carry it back to the blood stream.

BACTERIAL DISEASES OF THE BLOOD

ENDOCARDITIS
Subacute bacterial endocarditis involves the valves and lining of the heart chambers and is most often caused by oral streptococci, Viridans streptococci or by Staphylococcus epidermidis from the skin. The infection usually begins in structurally abnormal heart chambers in which the valves are damaged by previous disease or if there are congenital abnormalities of the valves or chambers. Chronic infections of the heart and pericardium are dangerous because they can lead to impaired circulation of blood and damage to vital organs from lack of oxygen. When there is release of endotoxin (by gram negative bacteria) this is more serious than when it is gram positive bacteriemia. Also caused by C. burnetii. Acute bacterial endocarditis is usually cased by virulent bacteria like Staphylococcus aereus or Streptococcus pnemoniae. This is a complication of infection elsewhere in the body. This disease can occur in the absence of a structural heart abnormality and can rapidly destroy heart valves.

Septicemia is often caused by Gram negative organisms mainly enterobacteria [like E. coli and Pseudomonas aeruginosa and Bacteroides (an anaerobe). Release of endotoxin from the organisms can cause shock and disseminated intravascular coagulation [because the circulating proteins responsible for blood clotting are activated by endotoxin].

Bacteria DISEASES OF THE LYMPH NODES and SPLEEN usually involve phagocytes.
Tularemia [also known as rabbit fever] is transmitted from wild animals via ticks and insects. The cause is a Gram negative aerobic rod, Francisell tularensis. Hunters and trappers are at risk for the disease. Ulcer formation at the entry site and enlargement of regional lymph nodes are characteristic.

Brucellosis [also known as Bang’s disease and undulant fever] is usually acquired from cattle or other domestic animals. Species of Brucella which are aerobic Gram-negative rods are the cause and pasteurization of milk is an important control measure. Workers at meat packing plants are at particular risk.
Yersinia pestis, a non-motile enterobacterium that upon staining looks like a safety pin, is the cause of plague [also known as black death]. It is now endemic in rodent populations in a number of states. It is transmitted by fleas causing ‘bubonic plague.’ Lung infection can spread directly person-to-person (that one is called ‘pneumonic plague).

VIRAL DISEASES OF THE LYMPHOID SYSTEM

Epstein Barr virus causes infectious mononucleosis [also known as mono or kissing disease].
The virus infects B lymphocytes which causes them to produce immunoglobulins and to proliferate. T cells bring the infection under control but latent infection persists in some B cells. It is also responsible for Burkitt’s lymphoma some of these B cells become immortal) and for nasopharyngeal carcinoma. Epstein Barr virus can establish lifelong latent infections in lymphocytes making them immortal. This is a key step in becoming cancerous.

Cytomegalovirus
[CMV] This is a virus of the Herpes family that can cause complications in immunocompromised hosts [remember this includes newborns, transplant patients as well as patients with immunocompromising diseases like AIDs and systemic lupus]. CMV causes fever, infectious mononucleoisis-like syndromes, loss of white blood cells, sore esophagis, belly, gradual loss of eyesight, and pneumonia [so we could have talked about it in association with other organ systems]. It is transmitted through body fluids of all kinds but needs access to the blood to infect. It also causes skin rashes and infections of the central nervous system and infection of the adrenal glands but these are rare complications.
Yellow fever is caused in humans by an arbovirus. Jungle primates are reservoirs of the disease. It causes fever, jaundice due to severe liver damage and hemorrhage.

PROTOZOAN INFECTIONS

Malaria is caused by four species of Plasmodium and is transmitted by Anophiles mosquitoes. Chills and fever correlate with the release of merozoites from infected red blood cells. Only gametocytes are infectious for the mosquito hosts, in which sexual reproduction of the plasmodia occurs. The worst infections are with P. falciparum.

Malaria has had two effects on the genes of humans.
One of these is that sickle cell confers some resistance to malaria. However, this may mean survival but the effects are severe.
The second has to do with selecting for certain genes to be more prevalent in malaria areas.