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Presented at an Interactive Workshop on Essentials of Epidemiology in Public Health at the Department of Social and Preventive Medicine University Malaya Kuala Lumpur Malaysia 19-25 October 2009 by Professor Omar Hasan Kasule Sr MB ChB (MUK), MPH (Harvard), DrPH (Harvard) Professor King Fahad Medical College Riyadh; Professor of Epidemiology and Islamic Medicine Institute of Medicine University Brunei Darussalam, Visiting Professor of Epidemiology University of Malaya
EPIDEMIOLOGICAL CHARACTERIZATION
Communicable or infectious disease is disease transferred from person to person by micro-organisms. Infection is lodging, growing, and multiplication of micro-organism in the host’s body. Invasion is mere presence of micro-organism without necessarily multiplying. Infectivity is the ability of the agent to lodge and grow in the host. Pathogenicity is the ability of the agent to cause disease. Virulence is the ability to cause severe disease. Pathogenicity is affected by invasiveness, toxigenicity, and hypersensitivity. Agents may invade tissues (eg shigella), produce toxins (eg botulinum), or cause allergic reactions (like Mycobacterium tuberculosis). An epidemic is said to occur when the epidemic threshold is breached. The term epidemic is used to refer to a wide-spread disease whereas the term outbreak is used to refer to localized disease. The communicable disease model comprises of the agent, the host, and the environment. Disease transmission occurs when a susceptible host and a pathogenic agent exist in an environment conducive to disease transmission. The primary attack rate is the number of new cases as a proportion of the total susceptible population. The secondary attack rate is the number of additional cases of disease among contacts of the primary or index cases within the maximum incubation period expressed as proportion of the total number of susceptible contacts. The case fatality ratio is number of fatal outcomes expressed as a proportion of the total number of cases with symptomatic illness.
THE AGENT: MICRO-ORGANISM
Microorganisms can be classified by structure as pro-karyotes (bacteria, rickettsiae, and Chlamydia), eukaryotes (fungi, protozoa, and helminths), and viruses; by transmission: feco-oral (ameba, giardia, shigella, vibrio cholera, salmonella spp, hepatitis virus A&E, polio virus, and tapeworms), soil contact (trichuris, ascaris, hookworms, strongyloides, and tetanus), water contact (schistosomiasis and guinea worm), skin contact (chickenpox and smallpox), air transmission (measles, pertussis, diphtheria, and tuberculosis), contact with body fluids (trachoma, syphilis, gonorrhea, and HIV), and arthropod-borne (dengue virus and the malarial protozoan); by infectivity, virulence, pathogenicity, toxigenicity, and the infective dose. They can be classified as saprophytic (live on dead organic matter), parasitic (depend on and harm the human host), commensals (depend on but do not harm the human host), and symbiotic (mutual benefit). Obligate parasites (e.g. viruses) cannot exist outside their host. Normal bacterial flora is opportunist pathogens.
Viral infections are recognized by detection of viral antigens or antibodies to viral antigens using serological technics (neutralization, hemagglutination inhibition, complement fixation, fluorescent antibody, radioimmunoassay, and ELISA) and cell culture. Diagnosis of bacterial infections is based on cultivation & identification, gram staining & microscopy, biochemical reactions, use of specific antibodies, and DNA hybridization. Fungal infections are less common, are by direct soil contact, inhalation, and rarely person to person transmission. They are localized and are rarely systemic. Diagnosis of fungal infection is difficult and is based on clinical or histological examination. Protozoa are single-celled eukaryotic organisms widely distributed in the world in both parasitic and free-living forms. The species that are epidemiologically important are plasmodium, toxoplasma, and pneumocytes. Plasmodia cause malaria that is the most important protozoal disease in terms of mortality and morbidity. P. falciparum causes more mortality and morbidity than P.ovale, P. vivax, and P. malariae. T.gondi has high prevalence with little clinical disease. P. carinii is an opportunistic infection in HIV/AIDS. Helminths are flat worms (cestodes), flukes (trematodes), and roundworms (nematodes). The most important helminths epidemiologically are schistosomiasis, hookworm, strongyloides, echinococcus, tenia, and toxicara.
Some microorganisms survive in reservoirs until they can infect humans. Common vehicle spread is by water, air or food. Serial transmission is human to human, human to animal to human, or human to environment to human. Infection can be exogenous or endogenous. Auto-infection found in strongyloides and E.coli. Horizontal transmission (human to another) is more common than vertical disease transmission (intra-uterine from the mother to fetus ?CMV, ?toxoplasma, ?rubella, ?HSV, ?syphilis, ?TB, ?VZ.). The natural portals of entry into human are the respiratory tract (common cold, influenza, measles, TB, whooping cough), the urogenital tract (gonorrhoea, syphilis, herpes, HIV), the alimentary tract (amebic dysentery, shigellosis, polio, and cholera), the mucous membranes, the skin, the placenta (rubella, syphilis, and HBV), and the parenteral portal (intravenious and sexual). The skin is a good natural barrier to infection but can be penetrated by insects, ticks, needles, and traumatic injuries. Air-borne infections are TB, influenza, histoplasmosis, and legionellosis. Vehicle borne transmission is by contaminated materials or objects (fomites). Vectors may be arthropods (such as mosquitoes, fleas, flies, lice, and ticks), zoonoses, plants, or other vehicles. They transmit organisms mechanically (eg flies and cockroaches) or hematophagous (eg ticks, lice, fleas, mites), or biologically. Biological transmission is more common than mechanical transmission. Zoonoses are diseases whose reservoirs are vertebrate animals and are transmitted to humans by accident for example plague, rabies, Rocky Mountain spotted fever. Anthroponooses are diseases whose reservoirs are human for example measles. Plants can be vectors of disease when they are contaminated by micro-organisms and are eaten raw. The concept of the communicable disease triangle simplifies discussion of communicable disease. The triangle consists of the agent, the host, and the disease. They interact among one another. Elements of the environment that affect disease transmission are: climate (temperature, rain, and wind patterns), vegetation (swamps, forest, and desert), water sanitation, air pollution, excreta disposal, housing, occupation (farm, factory). Poor sanitation and crowding increase the transmission of microorganisms. Breeding places near homes, forest reservoirs, and soil help the survival of organisms and their vectors.
THE HOST
Humans can be intermediate, definitive, reservoir, and accidental hosts. Humans can also be in a carrier status. They can be healthy, incubational, convalescing, or chronic carriers. Susceptibility to infection is determined by age, heredity, gender, pregnancy, nutritional status, life-style and behavior, personal hygiene, and immune resistance (natural or acquired; passive or active). Immune resistance is the main barrier to infection by micro-organisms.
THE DISEASE
Clinical severity can be described as mild, moderate, severe, and fatal. Clinical manifestations are: asymptomatic, latent, sub-clinical, and clinical. The 4 stages of the natural history are pre-pathogenesis, pre-clinical, clinical, and chronic.
Action | Period | ||
Infectiousness | Latent Period | Infectious Period | Non-infectious Period |
Disease | Incubation Period | Symptomatic Period | No disease Period |
An epidemic occurs due to changes in the agent, host susceptibility, and effective transmission. The agent may be new, may increase in number, or may change in virulence. An adequate susceptible population is required to sustain and propagate the epidemic.
CONTROL and PREVENTION OF COMMUNICABLE DISEASE
Control is by identification of cause, notification, treatment of cases using drugs, prevention, and surveillance. The strategy is attacking the agent at source, interrupting transmission, and reducing the susceptible population. Measures for the healthy host are active immunization, passive immunization, chemoprophylaxis, behavioral change (sexual, dietary), physical isolation, and increase of host resistance by better nutrition and health care. Measures for the diseased host are chemotherapy, isolation, quarantine, restriction of activity, and behavioral change. Vector control is by chemicals, environmental and biological control. Control of animal reservoirs is by active immunization, restriction of movement or reduction in number, chemoprophylaxis and chemotherapy. Environmental control is by water sanitation, safe drinking water, excreta disposal, and food sanitation. Control of the agent is by cleanliness, refrigeration, disinfection, and sterilization. Disease notification plays a central role in disease control. The notifiable diseases are: AIDS, anthrax, botulism, brucellosis, cholera, congenital rubella syndrome, diphtheria, encephalitis, gonorrhea, H. influenzae, Hansen’s disease, leptospirosis, lyme disease, measles, plague, paralytic polio, psittacosis, rabies, syphilis, tetanus, trichinosis, tularemia, typhoid, and typhus. Primary prevention is prevention of initial contact and/or infection. Non-epidemic secondary prevention consists of diagnosing and treating cases. Secondary prevention in an epidemic situation requires systematic investigation and taking specific control measures. Tertiary prevention limits chronic disability by physiotherapy, supportive care, and surgical correction of deformities. Among emerging infectious diseases are: Lyme disease due to a spirochete called borrelia burgdorferi, Legionnaire’s disease due to an agent in air-conditioning systems, the toxic shock syndrome due to a S. aureus toxin, Acquired Immunodeficiency syndrome, the esinophilia-myalgia syndrome due to toxic contaminants, the Hantavirus pulmonary syndrome due to hanta virus, enteropathogens (shigella spp, giardia, and HAV), opportunistic infections (p. carinii, cryptococcus spp), food borne infections (eg E coli), and the toxigenic vibrio.
COMMUNICABLE DISEASES BY VIRUSES
Presented at an Interactive Workshop on Essentials of Epidemiology in Public Health at the Department of Social and Preventive Medicine University Malaya Kuala Lumpur Malaysia 19-25 October 2009 by Professor Omar Hasan Kasule Sr MB ChB (MUK), MPH (Harvard), DrPH (Harvard) Professor King Fahad Medical College Riyadh; Professor of Epidemiology and Islamic Medicine Institute of Medicine University Brunei Darussalam, Visiting Professor of Epidemiology University of Malaya
VIRAL INFECTIONS: FECO ORAL
HAV infection is endemic, sporadic, and epidemic. There are no carriers. Travelers abroad are at higher risk. HEV is common in the Indian sub-continent. Pregnancy is associated with higher risk. Polio causes myositis, brain degeneration, and paralysis. It is endemic in less developed countries but rare in developed countries. It is commonest in both males and females at <5yr. It is rare in developed countries. Cocksackie infection occurs in an epidemic form. ECHO virus causes meningitis, and enteritis. It has world-wide distribution. Low SES. And & childhood are associated with higher risk. Rota-virus causes childhood enteritis. It has world-wide distribution. It is endemic and epidemic in the tropics. Children aged 6-24 months are at higher risk. Lassa virus causes Lassa fever first described in Nigeria
VIRAL INFECTIONS: AIR-BORNE
HSV 1 infection is more common in low SES and crowded conditions. VZ causes shingles/chicken pox with peak incidence is at ages 2-6 years. It is severe in infants and the immune compromised. Shingles in the elderly is reactivation of primary childhood infection. EBV infection LDC it is an asymptomatic childhood infection. In industrialized countries it is a symptomatic disease of young adults called infectious mononucleosis. Rhinovirus causes common cold. Measles virus causes measles. It is epidemic and endemic. Low SES and crowding are high risk factors. In LDC it is a disease of childhood. Adult infections occur in industrialized countries. Mumps virus: causes mumps. It is common in childhood. It may cause sterility due to oochitis. Rubella virus infection is endemic with higher infection risk in pregnancy and childhood. It is associated with the rubella syndrome in neonates. The influenza virus causes respiratory infection. It is seasonal, endemic, and epidemic. It manifests the phenomenon of antigenic drift. The elderly are at higher risk. Several influenza pandemics have been described over the past 3 centuries.
VIRAL INFECTIONS: VECTOR-BORNE
Yellow fever virus causes yellow fever. Focal outbreaks occur in Africa, S. America, & the Caribbean. YF infection is not found in Asia. Incidence is equal in males and females. All races and all ages are affected. Dengue virus causes dengue fever that can be severe in its hemorrhagic form. It is common in the tropics & subtropics. It is cyclic and seasonal. Incidence in males and females is equal and all ages are affected. Japanese encephalitis, caused by a flavivirus, is epidemic in Japan, Taiwan, and Korea. Children aged 5-14 years are at high risk. It is associated with cognitive impairment and neurological sequelae.
VIRAL INFECTIONS: PARENTERAL
HSV 2 infection is at high in the high-risk groups of the promiscuous and the homosexuals. CMV infection is endemic. The incidence rate of infection rises with age. Risk is higher in infants and the immune compromised. HBV infection causes hepatitis, a world-wide condition. The chronic carrier rate is 30% in the Middle East, the Far East, and sub-Saharan Africa. High risk groups are: homosexuals, Iv drug users, blood transfusion workers, health care personnel, and prostitutes. HBV is associated with cirrhosis and hapato-cellular carcinoma. HCV occurs world-wide. The carrier rate varies: Europe 0.2%, Far East 5%, and Middle-east 1-2%. Intravenous drug users and dialysis patients are at higher risk of infection. HDV infection occurs world-wide. It is endemic in the Mediterranean, N Europe, and USA. Intravenous drug users and multiple transfusions are higher risk factors. HIV causes AIDS. AIDS occurs world-wide. It is a current epidemic. Homosexuals, promiscuous heterosexuals, iv drug users, blood transfusion workers, health care workers are at higher risk.
VIRAL INFECTIONS: OTHERS
Rabies virus causes rabies. Its occurrence is endemic, epidemic, and sporadic. It has world-wide distribution especially in Asia, Africa, Central and South America. Veterinarians are at high risk of infection.
Key Words And Terms: Transmission, Feco-Oral, Transmission, Air Borne, Transmission, Parenteral, Endemic, Sporadic, Epidemic, Pandemic, Cyclic, Seasonal, Antigenic Drift, Carrier
COMMUNICABLE DISEASES BY PROKARYOTES
Presented at an Interactive Workshop on Essentials of Epidemiology in Public Health at the Department of Social and Preventive Medicine University Malaya Kuala Lumpur Malaysia 19-25 October 2009 by Professor Omar Hasan Kasule Sr MB ChB (MUK), MPH (Harvard), DrPH (Harvard) Professor King Fahad Medical College Riyadh; Professor of Epidemiology and Islamic Medicine Institute of Medicine University Brunei Darussalam, Visiting Professor of Epidemiology University of Malaya
BACTERIA INFECTIONS: FECO-ORAL
K. pneumonae causes diarrhea & respiratory tract infection. Shigella spp, the cause of shigellosis, world-wide in distribution with common epidemics. E. coli is world-wide in distribution and causes gastro-intestinal as well as urinary tract infection. Salmonella spp causes salmonellosis. It is distributed world-wide. It is both endemic and epidemic disease in addition to causing disease outbreaks. Cholera due to V. Cholerae is common in Asia especially in the rainy season. It is endemic in children and epidemic for all ages. H. pylori infection is associated with peptic ulcer. Prevalence of infection increases with age. Cl. botulinum causes botulism a severe form of food poisoning. Enteritis due to Compylobacter spp is world-wide affecting infants, young children, and young adults.
BACTERIAL INFECTIONS: DROPLET SPREAD
B. pertussis, the cause of pertussis and mental retardation, is both endemic and epidemic. Children below 5yr are at higher risk. Its incidence has been declining due to widespread availability of vaccination. C. diphtheriae causes diphtheria, myocarditis, and neurological complications. Its incidence is decreasing with mass vaccination. The risk of infection is increased by living in crowded conditions. H. influenzae causes URTI and meningitis. It is world-wide with risk of infection highest in young children under 5 years or immunecompromised children. S pyogenes, a cause of URTI, is world-wide in distribution with seasonal variations. S agalactae causes neonatal Infection. S fecalis causes UTI. S pneumonae causes pneumonia, URTI, and meningitis. It is world-wide in distribution occurring in both sporadic and epidemic forms. S viridans causes endocarditis. S aureus & S epidermidis cause skin infections, pneumonia, and food infection. They occur world-wide in both sporadic and epidemic forms. Tuberculosis due to M tuberculosis is world-wide in distribution with bi-modal peak incidences at ages 15-44 and 60+. Its incidence has been falling due to improved general living conditions and specific therapy. The recent rise of incidence is due to immuno-incompetence caused by HIV infection. The elderly, medical workers, and alcoholics are at higher risk of TB infection. M. leprae causes leprosy, a disabling condition common in the topics and sub-tropics and affecting males more than females. N. meningitidis causes meningitis. Its epidemiology is poorly understood. It is endemic and sporadic and is commonest in dry hot countries with display of strong seasonality.
BACTERIAL INFECTIONS: SEXUALLY TRANSMITTED
N. gonorrhoae infection is world-wide in distribution with rising incidence. It causes complications in females (cervicitis, pelvic inflammatory disease, ectopic pregnancy, chronic pelvic pain, and infertility), males (urethritis, epididymitis, and strictures), and infants (ophthalmia neonatorum, corneal ulceration leading to blindness and low vision, and low birth weight). Homosexuals and medical workers are at high risk for syphilis infection due to Tr. pallidum. Syphilis manifests as low birth weight, congenital syphilis, secondary syphilis, and tertiary syphilis (cardio-vascular complications, gummas, and neurosyphilis).
BACTERIAL INFECTIONS: OTHERS
Brucella spp is the cause of brucellosis with males, farm workers, and medical workers at higher risk. Plague due to Y. pestis is endemic in Africa, Asia, S. America, and Southern USA. B. anthracis causes anthrax (cutaneous & pulmonary) an occupational disease among persons working with animals or animal products condition that is rare in industrialized countries but common in developing countries. Tetanus due to Cl. tetani is rare in industrialized countries or where immunization is carried out. It occurs in an endemic form. Farmers, i.v. drug users, and newborns are at higher risk of infection. Leprospirosis due to Leptospira spp. is found more in rural areas. Hospital staff, estate workers, and school children are at higher risk of infection.
CHLAMYDIAL & RICKETTSIAL INFECTIONS
Typhus due to Rickettsia spp. occurs in both endemic and epidemic forms. It is commonest in the mountains of Ethiopia, S. America, and the Himalayas. Scrub typhus due to R. tsutsumagushi is found in Asia with farmers are at higher risk of infection. Cl. trichomatis causes ophthalmia neonatorum, neonatal pneumonia, low birth weight, and trachoma. Trachoma, which is corneal ulceration common in Africa & the Mediterranean region, leads to blindness and low vision both in neonates and adults. Cl. Trichomatis, found in Africa, Asia, and S. America, causes nonspecific genital infection (pelvic inflammatory disease, cervicitis, ectopic pregnancy, tubo-ovarian mass, chronic pelvic pain, infertility, urethritis, epididymitis, and urethral stricture). C burnetti causes Q fever. Spotted fever due to R Rickettsi is found in the eastern USA, S America, and Africa. People in tick infested areas are at high risk
Key Words And Terms: Transmission, Feco-Oral, Transmission, Air Borne, Transmission, Parenteral, Endemic, Sporadic, Epidemic, Pandemic, Cyclic, Seasonal, Antigenic Drift, Carrier
COMMUNICABLE DISEASES BY EUKARYOTES
Presented at an Interactive Workshop on Essentials of Epidemiology in Public Health at the Department of Social and Preventive Medicine University Malaya Kuala Lumpur Malaysia 19-25 October 2009 by Professor Omar Hasan Kasule Sr MB ChB (MUK), MPH (Harvard), DrPH (Harvard) Professor King Fahad Medical College Riyadh; Professor of Epidemiology and Islamic Medicine Institute of Medicine University Brunei Darussalam, Visiting Professor of Epidemiology University of Malaya
PROTOZOAL INFECTIONS
Giardiasis by G. Lamblia has world-wide distribution being most in the tropics. It occurs in both endemic and epidemic forms. Children and male homosexuals are at higher risk of infection. Trichomoniasis due to T. vaginalis is world-wide in distribution. African trypanasomiasis due to T.brucei is endemic in high-risk areas of East and Central Africa. American trypanasomiasis due to T. cruzi is common in Central and South America and is associated with cardiomyopathies, congestive cardiac failure, and megaviscera. Risk of infection is highest for children below 10 years and persons living in poor housing. Amebiasis due to E. histolytica is a world-wide endemic infection associated with poor sanitation. Malaria due to Plasmodium spp is common in the tropical and sub-tropical regions of Africa, Asia, and Latin America. Its incidence is higher in children. The infection is more severe in pregnancy due to the associated immune incompetence. It is associated with anemia, neurological sequelae, and renal complications. T. gondi causes toxoplasmosis which manifests as visceral leishmaniasis (kala-azar) or cutaneous leishmaniasis. It is world-wide with pregnant women and the immune compromised at higher risk. Leishmaniasis due to Leishmann spp. is found in the tropics, sub-tropics, the Mediterranean, and Middle Asia. It occurs in endemic, epidemic, and sporadic forms. Incidence in males is equal to that in females and all ages are affected. Interstitial pneumonitis due to P. carinii occurs world-wide. Risk of infection is high with low immunity and in HIV infection.
HELMINTHIC INFESTATIONS
Ascariasis due to A. Lumbricoides occurs world-wide and is very common. Incidence is highest in the tropics and sub-tropics. Higher risk is found in poor sanitation, farmers, and children. Clonorchiosis due to Cl. sinensis is commonest in Asia. Dracunculosis due to D. medinensis is common in Africa, the Middle-east, and the Indian sub-continent. W. bancriofti, B.malayi, and B timori cause filariasis which manifests as lymphedema and hydrocele. These are diseases more common in the rural areas of the tropical and sub-tropical regions of S. America, Africa, Asia, and the Pacific islands. They are more common in the rural areas. B malayi is found in Asia only. A duodenale & N americanus infestations are world-wide and endemic affecting all ages but with higher incidence in children aged 5-15 years. Farming, rural living, and childhood are risk factors of infection. Loa loa causes loaiasis (blindness, low vision, and itching) found in the topical rain forest of West and Central Africa. Onchocerciasis due to O. volvulus is found in equatorial Africa, Central and South America. Living near water is a high-risk factor for infection. Schistosomiasis is a disease of the tropical and subtropical regions of Africa, Asia, and S. America due to schistomiasis spp. S. hematobium and S.mansoni are world wide but S.japonicum is found only in Asia. Strongyloidosis due to S. stercoralis occurs world-wide. T. saginata & T. solium cause cycticercosis that is found world-wide especially in Asia, Africa, the Middle- east, and South America. T. trichuria causes trichuriasis (diarrhoea and anal pruritis) that is found world-wide. Toxicariasis caused by T. cani & T. cati is found world-wide and is related to working with dogs. Trichinosis caused by T. spiralis is found world wide being more common in the Americas, Asia, Africa, and the Artic. Fasciolasis is caused by F. hepatica. Hydatid disease, caused by E. granulosus, is endemic in Turkey, the Middle-east, Kenya, and S America. Enterobiosis, caused by E. vermicularis, is found world-wide with high prevalence in children, institutions, & families
FUNGAL INFECTIONS
Tinea cruris causes jock itch. Tinea pedis causes athlete’s foot.
Key Words And Terms: Transmission, Feco-Oral, Transmission, Air Borne, Transmission, Parenteral, Endemic, Sporadic, Epidemic, Pandemic, Cyclic, Seasonal, Antigenic Drift, Carrier
EMERGING COMMUNICABLE DISEASES
Presented at an Interactive Workshop on Essentials of Epidemiology in Public Health at the Department of Social and Preventive Medicine University Malaya Kuala Lumpur Malaysia 19-25 October 2009 by Professor Omar Hasan Kasule Sr MB ChB (MUK), MPH (Harvard), DrPH (Harvard) Professor King Fahad Medical College Riyadh; Professor of Epidemiology and Islamic Medicine Institute of Medicine University Brunei Darussalam, Visiting Professor of Epidemiology University of Malaya
OVER VIEW
The reemergence of infectious diseases in the developed countries after falling over most of the 20th century is due to socio-demographic, lifestyle or human behavior, environmental, and medical technological factors. The socio-demographic factors are: demographic changes (aging, migration), wide scale commercial and tourist travel, increasing crowding especially in the large urban areas, behavioral and lifestyle changes are factors contributing to emerging infectious diseases. Some diseases are old diseases and are old problems. Some diseases are old but are new problems for example tuberculosis and malaria. Some are new diseases with new pathogens such as Ebola and HIV. The environmental factors are climatic changes (global warming, climate change, rising sea levels, heat waves, and ozone depletion) that disturb the eco-system and thus favor growth and transmission of old and new pathogens. Immune suppression in organ donation and nosocomial infections are side effects of medical technology.
SEXUALLY TRANSMITTED DISEASES
Breakdown of traditional society and emergence of liberal ideas about sexual relations is behind the increase of STD. The traditional STDs are syphilis, gonorrhoea, and chanchroid. New diseases are chlamydia, genital warts, trichomonas, scabies, peduculosis, genital herpes, vaginal candidiasis, E. histolytica infection, G. lamblia, HVA, HBV, HCV, and HIV. Data on STDs is inadequate because of incomplete notification, non-uniform diagnostic criteria, and asymptomatic cases. Health education does not seem to be very effective in the prevention of STDs. Use of condoms by commercial sex workers is effective in decreasing STD incidence. Acquired Immunodeficiency syndrome (AIDS) appeared in 1981. The HIV 1 virus isolated in 1983 belongs to the retrovirus family. It attaches to the CD4+ lymphocytes which are depleted as the infection progresses. HIV is transmitted by semen, blood, vaginal and cervical secretions. Direct transmission occurs when contaminated syringe needles are shared by iv drug users, the perinatal period, breast milk, transfusion of blood and blood products, insemination with donated semen, transplantation of organs and tissues. Primary prevention consists of safe sex (monogamy or condom use), voluntary testing and contact tracing, safe blood supplies with use of antigen screening during the window between infection and appearance of antibodies, safe organ donation programs, precautions in medical facilities, and development of a vaccine.
VIRAL DISEASES
The Marburgh virus disease was first recognized in Yugoslavia and Germany when people fell ill after contact with monkeys imported from Uganda. The Ebola/Marburg virus epidemic started in 1976 and has been recurring being imported into Europe and the US by importation of monkeys from Africa. The A swine flu epidemic was recognized in 1976. Lassa fever spread is favored by urbanization leading to rodent exposure in the homes. Travel, migration, and urbanization contribute to spread of dengue fever and dengue hemorrhagic fever. The Hantavirus pulmonary syndrome due to hanta virus associated with contaminated droppings of deer mice appeared in 1993. Hanta viruses are spreading because of ecological and environmental changes that increase contact with rodents. Hepatitis B and C are spreading due to transfusion, organ transplantation, intravenous drug abuse, and sexual transmission. Rift valley fever transmission is favored by dam building, agriculture, and irrigation. Yellow fever is being transmitted in new areas because of conditions that favor mosquitoes.
BACTERIAL DISEASES
Streptococcus group A is an invasive necrotizing ‘flesh-eating’ bacterium whose increased transmission is not understood. The toxic shock syndrome due to infection of ultra absorbent tampons by Staphylococcus aureus appeared in 1980. Infections by enteropathogens such as Shigella are increasing. Cholera transmission is due to poor sanitation and introduction of new strains (such as O139) due to travel. The hemolytic uremic syndrome is due to mass food processing technology that allows Escheria coli O157:H7 to contaminate meat. Brazilian purpuric fever is due to a new strain of Hemophilus Influenzae. Helicobacter Pylori is probably not a new disease but has just been recognized as an association with gastric ulcers and other gastro-intestinal disorders. The decline of TB incidence in Europe and America registered in the 19th and 20 century due to socio-economic improvement started being reversed in the 1980s and 1990s due to bad social conditions (poverty, homelessness, and unemployment), infected immigrants, HIV infection, and rise of drug resistant TB. Control of TB is achieved by contact tracing, chemoprophyllaxis, and adherence to treatment schedules. Direct observed therapy (DOT) helps in ensuring treatment compliance. Shorter drug regimens also ensure that the problem of non-compliance does not arise. Prevention of TB is achieved by overall improvement in nutrition, social and environmental conditions, and alleviation of poverty. Primary prevention is based on BCG vaccination and chemoprophylaxis with INH which prevents reactivation of latent TB. Secondary prevention is treatment of multi-drug resistant conditions.
PARASITIC DISEASES:
Malaria is spreading due to increasing travel and migration. Schistosomiasis is spreading due to dam building. Lyme disease due to a spirochete called borrelia burgdorferi appeared in 1975. Its transmission is aided by reforestation around homes that favors the tick vector and the deer, a secondary reservoir host. Legionnaire’s disease is due to a small infectious agent spread via air-conditioning systems appeared in 1976. Biofilms that form on water tanks and plumbing favor growth of the causative organisms. P. carinii and Cryptococcus spp are opportunistic infections. Cryptosporidium spp, Cyclospora spp and other water-borne pathogens are due to contaminated surface water and improper water purification.
Key Words and Terms: New And Old Diseases, Reemerging Infectious Diseases, Socio-Demographic Factors, Environmental Factors, Medical Technology, Nosocomial Infections, Traditional Sexually Transmitted Diseases, Hiv/Aids, Marburgh/Ebola Virus, Swine Flu, Lassa Fever, Dengue Fever, Hanta Virus, Hepatitis, Rift Valley Fever, Yellow Fever, Streptococcus, The Toxic Shock Syndrome, Toxigenic Vibrio, Brazilian Purpuric Fever, Helicobacter Pylori, Tuberculosis, Malaria, Lyme Disease, Legionnaire’s Disease, Opportunistic Infections.