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Hematopoietic/Lymphoreticular System Infections

Neal R. Chamberlain, Ph.D.,

Professor, Department of Microbiology/Immunology

Specific Educational Objectives: The student should be able to:

1. Recite the most likely causes of the various diseases described in this handout and how these infections are usually acquired in the U.S. (modes of transmission for females and males can be different in some diseases).
2. Know what human cells the microbe interacts with if any.
3. In particular know how the HIV virus attaches with human cells. Also know the human cell receptors that the virus attaches to (hint: M-tropic vs. T-tropic viruses).
4. Be able to differentiate the diseases from one another based on clinical symptoms or laboratory tests. Examples: How is relapsing fever different from malaria? How is RMSF different from ehrlichiosis? How do you know a person has EBV mono and not CMV mono?
5. When definitions of a particular disease is included (AIDS) you should also know the definition.
6. Describe the various means of diagnosing these diseases and when to use which test.
7. List the most common opportunistic infections that occur in HIV/AIDS patients.
8. Know how each disease can be prevented.

OVERVIEW

The hematopoietic system consists of organs and tissues involved in the production of the cellular components of blood. Infections of lymphocytes, phagocytes, and erythrocytes will be discussed in this handout. The organs and tissues in the hematopoietic system include bone marrow, liver, lymph nodes, spleen, and thymus. The lymphoreticular system consists of the tissues of the lymphoid system and the mononuclear phagocyte system (reticuloendothelial system). The lymphoid system includes the thymus, bone marrow, lymph nodes, spleen, and the lymphoid tissues associated with the gastrointestinal tract (e.g., tonsils, Peyer patches). The mononuclear phagocyte system includes monocytes, macrophages, the endothelium lining the sinusoids of the spleen, lymph nodes, and bone marrow, and the fibroblastic reticular cells of hematopoietic tissues. The lymphoreticular and mononuclear phagocytic systems respond to infections and produce cells (e.g., bone marrow) or house cells (e.g., spleen, lymph nodes) that are part of the innate and acquired immune system.

Parts of the lymphoreticular system are also in  the hematopoietic system and as a result symptoms associated with many of the diseases of the lymphoreticular and hematopoietic system are similar and include splenomegaly, hepatomegaly, fever (recurring or constant), malaise, anorexia, and regional or generalized lymphadenopathy (Table H-1). Human immunodeficiency virus, Epstein Barr virus, and cytomegalovirus infections can all cause flu-like symptoms (e.g., malaise, fever, anorexia). Unfortunately, these symptoms are not specific and diagnosis of many of the infections can be difficult.

     EBV, Epstein-Barr virus; CMV, cytomegalovirus; HSV, herpes simplex virus; HIV, human immunodeficiency virus.

Some symptoms, however, can be relatively unique and help considerably in determining the causative agent. For example, inflammation of the lymph nodes can be a helpful clinical feature because certain infectious agents such as infectious mononucleosis tend to cause cervical lymphadenopathy. Other infections such as human immunodeficiency virus (HIV) cause generalized lymphadenopathy (see Table H-1). (Note that several of the diseases mentioned in Table H-1 will be or have been discussed in detail in other lectures). The pathology observed in the lymph nodes can also be helpful in narrowing down the cause of a particular lymphadenopathy (Table H-2).

Infectious agents such as the Plasmodium sp. infect erythrocytes and cause lysis of the cells resulting in recurrent fevers and in some cases severe anemia. The periodicity of recurring fevers in malaria, brucellosis, and relapsing fever can be helpful in determining a diagnosis. For example, a patient with relapsing fever tends to have a fever that lasts about 7 days, followed by the temperature returning to normal for about 7 days. The fever then returns for about 7 days and so on for three or four recurrences. On the other hand, a patient infected with the malaria parasite will have a fever for about 24 hours. Depending on the species of Plasmodium involved, the temperature will return to normal for 1 or 2 days, then the fever will return and last 24 hours, with several recurrences.

Some organisms such as Rickettsia rickettsii, the agent that causes Rocky Mountain spotted fever, infect and damage the endothelial cells resulting in hemorrhage into the skin. Bartonella henselae also can infect endothelial cells but will cause bacillary angiomatosis; a systemic disease resulting in multiple subcutaneous nodules, characterized histologically by vascular proliferation, in immunocompromised hosts (e.g., acquired immunodeficiency syndrome [AIDS] patients).

The infectious diseases that involve the hematopoietic and lymphoreticular systems are discussed in this handout according to the predominant host cell infected (Table H-3). Remember some of these organisms infect several of the cells in these systems, making this division of diseases somewhat arbitrary.

Revised 11/20/14

©2014 Neal R. Chamberlain, Ph.D., nchamberlain@atsu.edu

All rights reserved.

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