Emerging Infections Microbial Threats to Health in the United States (1992) / Chapter Skim
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2 FACTORS IN EMERGENCE
2 FACTORS IN EMERGENCE
Pages 34-112
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From page 34... ...
Although an infectious agent plays a role in any emerging infectious disease, other causative factors may be important as well. BOX 2-1 A Deadly Form of Strep It was a shock to many when renowned puppeteer Jim Henson died suddenly in May 1990.
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From page 35... ...
In the meantime, the Centers for Disease Control is working to track the new strep A more closely, with the hope of learning more about the bacterium and how to stop it. 35 Table 2-1 is a list of emerging infectious agents, categorized by type of organism.
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From page 36... ...
cough, sore throat, by direct contact pneumonia with secretions of an infected person Chlamydia Trachoma, genital Sexual intercourse Increased sexual trachomatis infections, conjunctiv- activity; changes in itis; infection during sanitation pregnancy can result in infant pneumonia Clostridium difficile Colitis: abdominal Fecal-oral transmis- Increased recognition; pain, watery diarrhea, sign; contact with the immunosuppression bloody diarrhea organism in the environment Ehrlichia Ehrlichiosis: febrile Unknown; tick is Increased recognition; chaffeensis illness (fever, head- suspected vector possibly increase in ache, nausea, host and vector vomiting, myalgia) populations Escherichia cold Hemorrhagic colitis; Ingestion of con- Likely due to the 0157:H7 thrombocytopenia; laminated food, development of hemolytic uremic esp.
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From page 37... ...
unpasteur ized milk; contact with infected pets Legionella Legionnaires' disease: Air-cooling systems, Recognition in an pneumophila malaise, myalgia, water supplies epidemic situation fever, headache, respiratory illness Listeria Listeriosis: Ingestion of contam- Probably increased monocytogenes meningoencephalitis inated foods; contact awareness, recognition, and/or septicemia with soil contami- and reporting nated with infected animal feces; inhala tion of organism Mycobacterium Tuberculosis: cough, Exposure to sputum Immunosuppression tuberculosis weight loss, lung droplets (exhaled lesions; infection can through a cough or spread to other organ sneeze) of a person systems with active disease Staphylococcus Abscesses, pneumonia, Contact with the or- Recognition in an aureus endocarditis, toxic ganism in a purulent epidemic situation; shock lesion or on the hands possibly mutation Streptococcus Scarlet fever, Direct contact with Change in virulence pyogenes rheumatic fever, infected persons or of the bacteria; (Group A)
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From page 38... ...
agent in cows sheep tissue Chikungunya Fever, arthritis, hemorrhagic fever Crimean-Congo hemorrhagic fever Hemorrhagic fever Bite of infected mosquito Bite of an infected adult tick Unknown Ecological changes favoring increased human exposure to ticks on sheep and small wild animals Dengue Hemorrhagic fever Bite of an infected Poor mosquito control; mosquito (primarily increased urbanization Aedes aegypti) in tropics; increased air travel Filoviruses (Marburg, Ebola)
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From page 39... ...
Animal-human virus reassortment; antigenic shift Antigenic drift Changing agricultural practices Increasing interface between human activity and endemic areas; discarded tires as mosquito breeding sites continued on next page
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From page 40... ...
mosquito Increased recognition Movement of mosquitoes and amplification hosts (horses) Lack of effective mosquito control and widespread vaccination; urbanization in tropics; increased air travel TABLE 2-1 Part 3: Examples of Emergent Protozoans, Helminths, and Fungi Related Mode of Cause(s)
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From page 41... ...
recreational activity Candida Candidiasis: fungal Endogenous flora; Immunosuppression; infections of the gastro- contact with secretions medical management intestinal tract, vagina, or excretions from (catheters) ; and oral cavity infected persons antibiotic use Cryptococcus Meningitis; sometimes Inhalation Immunosuppression infections of the lungs, kidneys, prostate, liver Cryptosporidium Cryptosporidiosis: Fecal-oral, Development near infection of epithelial person-to-person, watershed areas; cells in the gastro- waterborne Immunosuppression intestinal and respiratory tracts Giardia lamblia Giardiasis: infection of Ingestion of focally Inadequate control in the upper small contaminated food some water supply intestine, diarrhea, or water systems; bloating Immunosuppression international travel Microsporidia Gastrointestinal illness, Unknown; probably Immunosuppression; diarrhea; wasting in ingestion of focally recognition immunosuppressed contaminated food persons or water Plasmodium Malaria Bite of an infective Urbanization; Anopheles mosquito changing parasite biology; environmental changes; drug resis tance; air travel Pneumocystis Acute pneumonia Unknown; possibly Immunosuppression carinii reactivation of latent infection Strongyloides Strongyloidiasis: Penetration of skin or Immunosuppression; stercoralis rash and cough followed mucous membrane by international travel by diarrhea; wasting, larvae (usually from pulmonary involvement, fecally-contaminated and death in immune- soil)
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From page 42... ...
The return of dengue fever into areas of South and Central America where previously Ae. aegypti had been eradicated and the resurgence of yellow fever in Nigeria, where more than 400 persons were estimated to have died between April 1 and July 14, 1991 (Centers for Disease Control, unpublished data, 1992)
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From page 43... ...
Infections in animals that are transmissable to humans are termed zoonoses. As discussed in Chapter 1, throughout history rodents have been particularly important natural reservoirs of many infectious diseases.
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From page 44... ...
For example, field sampling and disease surveillance efforts have now identified more than 520 arthropod-borne viruses, or arboviruses (Karabatsos, 19854. The disease potential of most of these viruses is unknown, but nearly 100 have been shown to cause human disease (Benenson, 19901.
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From page 45... ...
Since the 1930s, 86 additional arboviruses have been found in North America. Fortunately, only a few, such as the California encephalitis complex, Colorado tick fever, and the dengue fever viruses, have been consistently associated with human disease.
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From page 46... ...
Studies are currently in progress at the U.S. Army Medical Research Institute of Infectious Diseases (USAMRIID)
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From page 47... ...
Although it is a difficult, if not impossible, task to predict the emergence of "new" infectious diseases/agents, it is helpful to understand the factors that facilitate the emergence and spread of infectious diseases in general. We must focus on what we do know: the infectious disease that will emerge or reemerge is likely to do so through one or more of the "facilitative pathways" diagrammed in Figure 2-1.
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From page 48... ...
Increases in the size, density, and distribution of human populations can facilitate the spread of infectious agents; changes in the distribution of populations can bring people into contact with new pathogenic organisms or with vectors that transmit those organisms. Immunosuppression, a by-product of aging, the use of certain medications, diseases, or other factors, often permits infection by microorganisms that are not normally pathogenic in humans.
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From page 49... ...
to shock and fatal hemorrhagic disease (dengue hemorrhagic fever/dengue shock syndrome EDHF/DSSi)
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From page 50... ...
The lack of effective mosquito control in many tropical urban centers a by-product of economic and political problems as well as indifference has undoubtedly contributed to the dramatic rise in dengue infection worldwide. The United States experienced dengue fever outbreaks in 1922 and 1945 (Langone, 1990~.
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From page 51... ...
Aedes aegypti and Ae. albopictus, both vectors of diseases such as dengue fever, viral encephalitis, and yellow fever, prefer to lay their eggs in water that collects in containers.
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From page 52... ...
Infections caused by typically nonthreatening organisms that take advantage of a person's weakened state are called opportunistic infections. Although opportunistic infections have received a great deal of attention over the past decade with the onset of the HIV disease pandemic, they are not new.
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From page 53... ...
For example, an estimated 80 percent of Americans are infected with cytomegalovirus (CMV) , a herpesvirus (National Institute of Allergy and Infectious Diseases, l991b)
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From page 54... ...
In contrast to some fungal and other bacterial infections that occur only in the late stages of HIV disease, TB is a sentinel disease for HIV infection and tends to occur prior to other opportunistic infections, often before individuals realize they are HIV seropositive. In healthy individuals, pulmonary tuberculosis can be diagnosed and treated with relative ease (the cure rate is approximately 95 percent)
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From page 55... ...
Although the earliest documented case of HIV infection was obtained from a serum sample collected in central Africa in 1959 (Gerry, 1990) , the country or continent in which the HIV disease epidemic began is not known.
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From page 56... ...
Although in the United States, HIV infection occurs predominately in male homosexuals and intravenous substance abusers, the rate of infection among non-substance-abusing heterosexuals is increasing. The fact that HIV first established itself in the United States mainly among gay men has both negative and positive repercussions.
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From page 57... ...
TECHNOLOGY AND INDUSTRY Notwithstanding all of their benefits, technology and industry may directly or indirectly cause the emergence of infectious diseases. Modern medicine has created situations that are ideally suited for the emergence of infectious agents.
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From page 58... ...
Although hospital sanitation has improved markedly since the late nineteenth century, when carbolic acid was first used as an antiseptic during surgery, nosocomial infections continue to challenge efforts to control them (Fuchs, 1979~. Medical advances and antimicrobial resistance are at the heart of the struggle.
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From page 59... ...
The most common of these (and the most frequent of all nosocomial infections) is urinary tract infection (UTI)
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From page 60... ...
, HIV-1, and, recently, HIV-2 as well. HIV-2 currently ranks as the primary cause of HIV disease only in West Africa; yet as of September 1991, 31 people in the United States had been diagnosed with HIV-2 infection, making the virus a potential threat to the safety of the blood supply in this country (Johnston, 1991)
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From page 61... ...
Compared with hospital-based programs, infection control programs in many long-term care facilities are rudimentary, at best. Unlike hospital-based programs, there are no standardized criteria for defining nosocomial infections in long-term care facilities; in addition, adequate studies designed to assess the efficacy of their surveillance and control measures have not been conducted.
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From page 62... ...
This network makes it possible for nosocomial and community-acquired infections to be rapidly and widely spread. PREVENTION OF NOSOCOMIAL INFECTIONS Studies show, surprisingly, that even under the most sanitary of conditions, only about a third to a half of all hospital-acquired infections are preventable (Schaechter et al., 1989; Martone, 1990~.
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From page 63... ...
There has been a substantial increase in our knowledge of food-borne diseases during the past 20 years, as reflected in an approximate tripling of the list of known food-borne pathogens. An important component of this increase in understanding is a better scientific grasp of the factors that allow microorganisms, and bacteria in particular, to cause human disease.
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From page 64... ...
Broad-based societal events indirectly related to agriculture may also affect food safety. Recent concerns about bovine spongiform encephalopathy
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From page 65... ...
To date, however, no human infections have been detected. In addition to modifications of traditional farming methods, the introduction of new types of agriculture can have an impact on the emergence of microbial threats.
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From page 66... ...
66 EMERGING INFECTIONS as simple as a change in packaging can be important. For example, plastic overwraps for packages of fresh mushrooms were introduced in 1967 because they enhanced the keeping-quality of this highly perishable food.
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From page 67... ...
For example, when estuarine areas are developed for residential or recreational purposes, water treatment capacity often lags behind requirements imposed by the population increase. In some cases, potentially dangerous viral and bacterial pathogens are released into the water from sewage effluent and storm-drain runoff, where they are concentrated by shellfish and subsequently harvested and consumed, often with minimal processing.
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From page 68... ...
This will necessitate the further development and implementation of international standards, such as the Codex Alimentarius of the Joint Food and Agricultural Organization/World Health Organization Food Standards Programme. International commerce can affect food safety, even when the food itself is not being transported.
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From page 69... ...
residents to new foods. Although popular, some of these foods, or the ways in which they are prepared, can cause disease as a result of contamination by any number of organisms or their toxic byproducts.
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From page 70... ...
A Norwalk-like virus was apparently introduced into the well by a faulty sewage treatment facility nearby, whose untreated sewage passed through fractures in the sandstone and limestone fields surrounding the well (Lawson et al., 1991~. Water used for recreational purposes can also be the source of waterborne infectious disease outbreaks, caused by pathogens such as hepatitis A virus (Bryan et al., 1974)
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From page 71... ...
Public health authorities, however, are especially mindful of potential outbreaks following natural disasters, such as earthquakes and hurricanes, that can lead to contamination of municipal water supplies. ECONOMIC DEVELOPMENT AND LAND USE Dam Building and Rift Valley Fever Until relatively recently, Rift Valley fever, which is caused by a mosquito-borne virus, occurred only in Africa south of the Sahara and was primarily a disease of sheep and cattle.
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From page 72... ...
In the United States, the virus could enter in the blood of an infected person or by way of an animal imported into a wildlife park or zoo. This is an admittedly unlikely possibility; nevertheless, should Rift Valley fever virus become established in vectors in this country, its control would require expensive, integrated efforts including vaccination of domestic livestock and extensive measures to kill vector mosquitoes.
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From page 73... ...
The first recognized outbreak of Lyme disease occurred in coastal Connecticut
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From page 74... ...
in 1975 (Steere et al., 19771. In 1975 and 1976, 51 people living in and around the town of Old Lyme, Connecticut, suffered from a condition that was tentatively diagnosed as juvenile rheumatoid arthritis and later as Lyme arthritis, in recognition of the focus of the epidemic.
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From page 75... ...
SOURCE: D Dennis, Division of Vector-Borne Infectious Diseases, Centers for Disease Control.
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From page 76... ...
A variety of etiologically distinct infectious agents are transmitted by the same ticks and maintained in the same rodents that perpetuate the agent of Lyme disease (Spielman, 19881. In the United States, babesiosis, a malarialike disease caused by Babesia microti, has been diagnosed in people living in or near the same areas in which Lyme disease is prevalent.
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From page 77... ...
Based on current knowledge, however, this committee believes that the impact of population growth (particularly when it leads to high population density) is likely to have a more predictable effect on the emergence of infectious diseases than the projected changes in global temperatures.
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From page 78... ...
MALARIA Malaria, considered one of the greatest contemporary killers among infectious diseases, is no longer endemic to this country but is one of the diseases that is most frequently imported. The CDC reported 1,173 imported malaria cases in 1991 (Centers for Disease Control, 1992b)
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From page 79... ...
The ease with which people can travel around the world today means that "exotic" diseases can move just as quickly. Physicians must be consistently aware of infectious diseases that originate in other parts of the world, and vigilant about obtaining a travel history for patients with undiagnosed illness, especially if it is accompanied by fever.
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From page 80... ...
SOURCE: Centers for Disease Control, l991h. Until the mid-1970s, most cases of imported malaria in the United States occurred in war veterans who had acquired the disease while on overseas duty.
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From page 81... ...
States in the Southwest and along the Gulf of Mexico are at particular risk for malaria because of their proximity to the border with Mexico, where many of the illegal immigrants gain access to the United States. Commerce The international transportation of goods has indirectly led to the emergence of a number of infectious diseases.
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From page 82... ...
The hantaviruses have also found their way into laboratory rodent colonies, in which they cause chronic, asymptomatic infections (LeDuc, 19874. Serious human disease and death have been documented in animal handlers, scientists, and others who unknowingly have been exposed to hantaviruscontaminated rat colonies.
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From page 83... ...
Scientists at the U.S. Army Medical Research Institute of Infectious Diseases (USAMRIID)
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From page 84... ...
a number of genes and gene products that enable them to do so. These gene products are extremely varied, but they include factors involved in transmission from one host to another, in cell-surface attachment and invasiveness, in countering or suppressing specific and nonspecific host immune responses, in persisting or surviving inside and outside a host organism, and in resistance to antimicrobial drugs.
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From page 85... ...
On the one hand, their mutation rates are extraordinarily high (because unlike DNA viruses, RNA viruses have no mechanisms for correcting errors made during replication)
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From page 86... ...
Influenza A Virus Although influenza viruses mutate at a rate similar to other RNA viruses, they are unique in that they also evolve (undergo meaningful changes) relatively rapidly in nature.
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From page 87... ...
HIV-1 and HIV-2, the two known HIV viruses, exhibit extensive genetic variability and exist in infected individuals as a complex mixture of closely related genomes, or quasispecies. These quasispecies undergo rapid genetic change such that the major viral form present in chronically infected persons differs over time.
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From page 88... ...
Also reassuring is the general experience that evolutionary adaptation of pathogens tends toward lesser virulence. DNA VIRUSES Hepatitis B Virus Hepatitis B is a DNA virus, but because it uses reverse transcriptase to replicate, it shares with RNA viruses the tendency to undergo significant and rapid genetic change.
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From page 89... ...
B ACTERIA Bacteria cause disease because they produce so-called virulence factors.
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From page 90... ...
Whatever the mechanism, the emergence of enhanced virulence potential is observed within time intervals measured in days or hours. Brazilian Purpuric Fever The most recent example of the emergence of a new disease that is likely to have been the result of a mutation causing enhanced virulence occurred in 1984.
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From page 91... ...
FACTORS IN EMERGENCE 91 TABLE 2-4 Representative Examples of Virulence Factors Encoded by Bacteriophages, Plasmids, and Transposons Mobile Genetic Element Organism Virulence Factor Streptococcus pyogenes Esche~ichia cold Staphylococcus au' eus Clost~idium botulinum Co' ynebacte' ium diphthe' iae Plasmid Transposon Erythrogenic toxin Shiga-like toxin Enterotoxins A D E Staphylokinase TSST-1 toxin Neurotoxins C D E Diphtheria toxin Escherichia cold Bacillus anthracis Ye~sinia species Ye~sinia pestis Escherichia cold Shigella dysente' iae Vibrio cholerae Enterotoxins LT, ST Pili colonization factor Hemolysin Urease Serum resistance factor Adherence factors Cell invasion factors Edema factor Lethal factor Protective antigen Poly-D-glutamic acid capsule Intracellular growth factor Capsule production factor Coagulase Fibrinolysin Murine toxin Heat- stable enterotox ins Aerobactin siderophores ? Hemolysin and x-pill operons ?
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From page 92... ...
Thus, resistance to antimicrobials or pesticides is a critical factor in the emergence of infectious diseases. RESISTANCE TO ANTIBIOTICS An increasingly important contributor to the emergence of microbial threats to health is drug resistance.
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From page 93... ...
Treating resistant infections requires the use of more expensive or more toxic alternative drugs and longer hospital stays; in addition, it frequently means a higher risk of death for the patient harboring a resistant pathogen. Estimates of the cost of antibiotic resistance in the United States annually range as high as $30 billion (Phelps, 1989~.
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From page 94... ...
This finding is particularly worrisome, since these organisms are becoming a major cause of nosocomial infections in this country. Pseudomonas aeruginosa Pseudomonas aeruginosa is an important cause of nosocomial infections, especially in the immunocompromised patient (Schaberg et al., 19914.
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From page 95... ...
In 1984, 52 percent of patients were infected with tubercle bacilli resistant to at least one drug, and 32 percent were resistant to one or more drugs (Marwick, 19924. Outbreaks of MDRTB have been reported in 13 states.
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From page 96... ...
For patients whose tubercle bacilli are thought to be resistant to isoniazid, a fourth drug, ethambutol, should be added to the regimen until drug susceptibility results are known. Isolates of tubercle bacilli resistant to both isoniazid and rifampin, now representing about 20 percent in some cities, require specialized treatment with additional medications, which may include streptomycin and ciprofloxacin for almost two years.
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From page 97... ...
SOURCE: D Snider, Jr., Division of Tuberculosis Control, National Center for Prevention Services, Centers for Disease Control.
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From page 98... ...
Trifluridine (topical) Vidarabine Zidovudine Herpes simplex virus Varicella-zoster virus Influenza A Human immunodeficiency virus-1 Human immunodeficiency virus-1 Cytomegalovirus Herpes simplex virus Cytomegalovirus Herpes simplex virus Herpes simplex virus Herpes simplex virusa Herpes simplex virusa Human immunodeficiency virus-1 aResistance to these drugs can be demonstrated in the laboratory but has not yet been documented in clinical isolates.
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From page 99... ...
. Resistance to acyclovir was a relatively uncommon event prior to the onset of the HIV disease pandemic.
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From page 100... ...
Zidorudine and Human Immunodeficiency Virus-l Zidovudine, also known as azidothymidine (AZT) , is effective in prolonging the survival and improving the quality of life of those infected with HIV-1, including those with AIDS, those with symptomatic HIV infection, and HIV-infected asymptomatic individuals.
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From page 101... ...
Given the distribution of malaria cases throughout the world, drug resistance is of much greater concern outside the United States than within it. Still, the potential for the reemergence of malaria in this country, and the role of drug resistance in such a scenario, cannot be overlooked.
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From page 102... ...
The recognition that an "old" disease, with heretofore unknown causes, is associated with an infectious agent is one of the more interesting ways infectious diseases emerge. A number of diseases are now thought to be caused by microbial infection or to involve microbes as cofactors in pathogenesis.
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From page 103... ...
Affective treatment Is not ava~an~e, and cteatn usually occurs within one year of diagnosis. Fortunately, only 2 to 5 percent of HTLV-I-infected persons develop ATLL (Murphy et al., 1989~.
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From page 104... ...
In humans, two similar viruses, herpes simplex virus (HSV-1 and HSV-2) and cytomegalovirus (CMV)
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From page 105... ...
Cervical cancer is uniquely amenable to secondary prevention by screening and early treatment since it evolves through surgically curable premalignant stages to invasive disease over a 10- to 20-year period (Tabbara et al., 1992~. Other factors besides HPV infection, however, play a role in the development of cervical cancer.
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From page 106... ...
HPV infection and cervical disease also progress more rapidly and are more refractory to treatment in women with HIV infection. As the prevalence of heterosexually transmitted HIV increases among women, HPV infection and cervical disease will continue to emerge as major opportunistic complications.
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From page 107... ...
disease caused by the bacterium Vibrio cholerae, reached epidemic levels in South America in January 1991 for the first time in almost a century. Inadequate sanitation played a role in its reappearance, which occurred initially in several coastal cities in Peru; then the disease spread through much of the continent.
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From page 108... ...
The emergence of HIV disease and AIDS swung the pendulum back to infectious diseases. HIV disease and the host of opportunistic infections that accompany it have severely challenged the scientific, medical, and public health communities, as well as politicians.
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From page 109... ...
This phenomenon is a danger to all countries, particularly those with poor or inactive immunization programs (see Table 2-74. The incidence of measles, a highly communicable viral disease, declined rapidly in the United States after the introduction of an effective vaccine in 1963.
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From page 110... ...
military forces are at high risk of being exposed to a variety of infectious disease agents. In past conflicts, infectious diseases have produced higher hospital admission rates among U.S.
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From page 111... ...
The return of TABLE 2-8 Infectious Diseases Causing High Morbidity in U.S. Forces in Past Conflicts: World War II, Korea, Vietnam, and Operation Desert Storm Disease Category Acute respiratory diseases and influenza Acute diarrhea!
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From page 112... ...
The following examples describe infectious diseases that have emerged in association with military operations, some of which involved U.S. troops.
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