Host Defense and Communication

Unit 4

This unit focuses on an understanding of and responses to infectious and immune-mediated syndromes. The professional identity component continues with an emphasis on communication in physician-patient and physician-community relationships. Using case-based learning in small groups, learners analyze typical inflammatory and infectious syndromes with an emphasis on the immune response, disease pathogenesis, clinical evaluation, management, and public health. Learners gain an appreciation of the dynamic interactions of different molecules, cells, and tissues that contribute to immunity to promote the optimal regulation of the body and immune defenses. It is important for learners to understand how the human body defends itself from pathogens and how the osteopathic physician, as a member of a medical team, can assist in that endeavor to prevent and treat infections.


As osteopathic medicine has recognized since its inception, one of the great marvels of the human body lies in its capacity to defend itself from threats and heal itself. One can hardly fail to be struck by the immune system’s dynamic ability to generate a tremendous variety of molecules and cells capable of recognizing and eliminating foreign invaders. This awe prompted scientific and medical curiosity, particularly as people in the 18th Century, and before, recognized that their fellow human beings who survived the ravages of epidemic disease were generally unaffected upon exposure to the same pathogen a second time. Around 1798, Edward Jenner observed that milkmaids who had contracted the relatively mild cowpox exhibited subsequent immunity to the far more severe smallpox.1 This observation led to the development of the world’s first smallpox vaccine. To date, vaccination represents one of the greatest triumphs of modern medicine.

The germ theory of disease, which states that certain diseases are caused by the presence of specific microorganisms in the body, gained acceptance in the mid-to-late 1800s and was based on almost 200 years of hypothesis testing. Coincidentally, urbanization of the United States led to major advances in the fields of sanitation and public health throughout the 19th century.2 The compatibility of these two fields of research led to revolutionary changes in the practice of medicine and prevention of the spread of disease. Theories related to humoral and cell-based immunity followed, and thus, the fields of microbiology and immunology were born.

Infectious diseases account for a quarter of deaths worldwide, and a handful of deadly infectious diseases claim ten million lives each year: lower respiratory tract infections, diarrheal diseases, HIV/AIDS, tuberculosis, and malaria (The National Academy of Sciences, 2016). Since the start of the HIV/AIDS epidemic, an estimated 78 million people have become infected with HIV, and 35 million people have died of AIDS-related illnesses.3 Even less lethal viral infections such as influenza, chicken pox, and hepatitis cause substantial morbidity. Infections for which there are effective immunizations such as measles, mumps, and rubella are again on the rise as some parents object to vaccinations.

Comprehension of the complex processes that constitute an optimal immune response is critical to interpreting deviations of immunity that result in immune-mediated diseases and failures of host defense. This unit will explore the osteopathic approach to treating infectious and inflammatory diseases. The use of manual manipulation techniques for pneumonia was first recorded as early as the Spanish influenza pandemic of 1918, when patients treated with standard medical care had an estimated mortality rate of 33%, compared to a 10% mortality rate in patients treated by osteopathic physicians.4 Since these early years, osteopathic physicians have worked with patients to promote the optimal regulation of their patients’ bodies and immune defenses. By means of their care and its heritage, osteopathic physicians have served as hosts to their “guests”—their patients—in the environment of the clinical home.



1Edward Jenner. "An Inquiry into the Causes and Effects of the Variolae Vaccinae, Or Cow-Pox. 1798". The Harvard Classics, Vol. 38, 1909-1914.

2Barnard, FAP. The Germ Theory of Disease and its Relations to Hygiene. Public Health Pap Rep. 1873; 1: 70–87.

3UNAIDS Fact Sheet:, 2016.

4Smith RK. One hundred thousand cases of influenza with a death rate of one-fortieth of that officially reported under conventional medical treatment. J. Am. Osteopath. Assoc. 1920; 20:172–17.