S . typhi are pathogenic exclusively in humans. The source of infection is sick human or bacteriocarrier. People are typically infected with S . typhi through food and beverages contaminated by a chronic stool carrier (fecal-oral route of transmission) . Less commonly, carriers may shed the bacteria in urine , saliva and breast milk . Typhoid fever is potentially fatal if untreated.
Typhoid fever occur worldwide but primarily in developing nations where sanitary conditions are poor. It is endemic in Asia, Africa, Latin America, the Caribbean, and Oceania. Typhoid fever affects 13-17 million people yearly and kills an estimated 600,000.
Early antibiotic therapy has transformed a previously life-threatening illness of several weeks ’ duration with an overall mortality rate approaching 20% into a short-term febrile illness with low mortality.
Travelers to endemic countries should avoid raw unpeeled fruits or vegetables since they may have been prepared with contaminated water; in addition, they should drink only boiled water.
In endemic countries, the most cost-effective strategy for reducing the incidence of typhoid fever is the institution of public health measures to ensure safe drinking water and sanitary disposal of excreta.
Shigellosis is general infectious disease caused by bacterium of genus Shigella , characterized by principal damage of mucous membrane of distal section of the large intestine, accompanied by symptoms of general intoxication, abdominal spastic pain, and frequent watery stool with admixture of mucus and blood, and tenesmus.
Shigellosis is spread by means of fecal-oral transmission. Other modes of transmission include ingestion of contaminated food or water, contact with a contaminated inanimate object, and sexual contact. Vectors like the housefly can spread the disease by physically transporting infected feces.
It is usually contracted by ingesting raw or undercooked eggs, or from sources such as p oultry , pork , and cattle , if the meat is prepared incorrectly or somehow becomes infected with the bacteria ; i nfected eggs and milk, as well as egg products, when not prepared, handled, or refrigerated properly ; r eptiles such as turtles , lizards , and snakes , as they can carry the bacteria on their skin ; p et rodents .
One of the more common causes of acute hepatitis is hepatitis A virus (HAV). The hepatitis A virus is a single-stranded, positive-sense, linear RNA enterovirus and a member of the Picornaviridae family. The hepatitis A virus is an icosahedral nonenveloped virus measuring approximately 28 nm in diameter.
Hepatitis A virus as viewed through electron microscopy.
Acquisition results almost exclusively from ingestion. Humans appear to be the only reservoir for the hepatitis A virus. Most patients have no defined risk factors for hepatitis A. Risk factors for acquisition of hepatitis A include the following:
Personal contacts ;
Occupation (eg, daycare) ;
Foreign travel ;
Male homosexuality ;
Illicit parenteral drug use ;
Persons in high-risk populations (eg, sewage workers, childcare workers, aid workers, male homosexuals).
Globally, hepatitis A virus infection is often asymptomatic and subclinical. Approximately 75% of adults are symptomatic with infection, many with jaundice. 90% of those infected before age 2 years are asymptomatic. The overall case fatality for acute hepatitis A virus infection is 0.02-0.1%.
Hepatitis E virus (HEV) is an enterically transmitted self-limited infection. It has many similarities with hepatitis A. HEV is icosahedral and nonenveloped. It has a diameter of approximately 34 nanometers and contains a single strand of RNA.
Hepatitis E is spread by fecally contaminated water within endemic areas. Outbreaks can be epidemic and individual. It has worldwide distribution, but predominating factors include tropical climates, inadequate sanitation, and poor personal hygiene. The reservoir of HEV is unknown, but it may be transmitted by animals. It predominantly affects those aged 15-40 years. It may affect younger age groups but generally is not recognized and may be subclinical. Although predilection is unknown, pregnant women are prone to complications. No chronic cases have been described.
The overall case fatality rate is 4%. The case fatality rate among pregnant women is 20%, which increases during the second and third trimesters. Reported causes of death include encephalopathy and disseminated intravascular coagulation.
Diphtheria is an acute toxin-mediated disease caused by Corynebacterium diphtheriae and characterized by sore throat, low fever , and an adherent membrane (a pseudomembrane) on the tonsils , pharynx , and/or nasal cavity. A milder form of diphtheria can be restricted to the skin.
Etiology Corynebacteria are gram-positive, catalase-positive, aerobic or facultatively anaerobic, generally nonmotile rods. Humans are the only known reservoir for the disease. The primary modes of dissemination are by airborne respiratory droplets, direct contact with droplets, or infected skin lesions. Asymptomatic respiratory carrier states are believed to be important in perpetuating both endemic and epidemic disease. Immunization reduces the likelihood of carrier status.
Mortality/Morbidity Mortality rates are highest at the extremes of age and in insufficiently immunized persons. However, even partial immunization confers a reduced risk of severe disease. Death usually occurs within the first week, either from asphyxia or heart disease.
Vaccination Childhood immunization is the prevention method of choice. Diphtheria/tetanus/pertussis (DTP) vaccine, given at ages 2, 4, and 6 months; at age 15-18 months; and at least 5 years later (age 4-6 y) is the immunization regimen.
INFLUENZA Influenza virus infection, one of the most common infectious diseases, is a highly contagious airborne disease that causes an acute febrile illness and results in variable degrees of systemic symptoms, ranging from mild fatigue to respiratory failure and death.
People who contract influenza are most infective between the second and third days after infection, and infectivity lasts for around ten days. Influenza can be spread in three main ways:
by direct transmission (when an infected person sneezes mucus directly into the eyes, nose or mouth of another person);
the airborne route;
and through hand-to-eye, hand-to-nose, or hand-to-mouth transmission, either from contaminated surfaces or from direct personal contact such as a hand-shake.
Mortality/Morbidity The influenza is responsible for an average of more than 20,000 deaths annually. Elderly people are at higher risk for complications of influenza A and B.
MEASLES Measles is a highly communicable acute disease. It is also known as rubeola and is marked by prodromal fever, cough, coryza, conjunctivitis, and pathognomonic enanthem (ie, Koplik spots), followed by an erythematous maculopapular rash on the third to seventh day.
Etiology and Epidemiology Measles virus , a negative-sense enveloped RNA virus, is a member of the Morbillivirus genus in the Paramyxoviridae family. The highly contagious measles virus is spread by coughing and sneezing via close personal contact or direct contact with secretions. In temperate areas, the peak incidence of infection occurs during late winter and spring.
Children with immunodeficiency due to HIV or acquired immunodeficiency syndrome (AIDS), leukemia, or corticosteroid therapy, regardless of immunization status;
Travel to areas where measles is endemic or contact with travelers to endemic areas;
Infants who lose passive antibody prior to the age of routine immunization.
Mortality/Morbidity Measles is still a leading cause of death among children, despite the availability of an effective vaccine. Highest fatality rates are among infants aged 4-12 months and in children who are immunocompromised because of human immunodeficiency virus (HIV) infection or other causes.
MENINGOCOCCAL INFECTIONS Meningococcal infections (known as meningococcemia) can range in severity from a transient bacteremia that is relatively benign to an overwhelming infection that is rapidly fatal. N. meningitidis is a gram-negative diplococcus that grows well on solid media supplemented with blood and incubated in a moist atmosphere enriched with carbon dioxide.
Epidemiology The human nasopharynx is the only known reservoir for N. meningitidis. Meningococci spread from person to person by airborne droplets of infected nasopharyngeal secretions.
Fulminant meningococcemia carries the highest mortality rate; it can exceed 50% despite the use of appropriate antibiotic therapy. It can be as high as 70% in developing countries. Survivors of fulminant meningococcemia may have ischemic complications.
Meningococcal meningitis without antibiotic therapy is uniformly fatal.
Prevention Antimicrobial chemoprophylaxis of close contacts is the primary means of preventing secondary cases of sporadic meningococcal disease. Person-to-person transmission can be interrupted by administration of an antimicrobial that eradicates the asymptomatic nasopharyngeal carrier state. Sulfonamides, rifampin, minocycline, ciprofloxacin, and ceftriaxone are the drugs that have been shown to eradicate meningococci from the nasopharynx.
The most important form of prevention is a vaccine against N. meningitidis. The commonly used vaccines are:
MUMPS Mumps or epidemic parotitis is a viral disease of the human species, caused by the mumps virus . Painful swelling of the salivary glands (classically the parotid gland ) is the most typical presentation. Painful testicular swelling ( orchitis ) and rash may also occur.
Etiology Mumps is a single-stranded RNA virus and a member of the family Paramyxoviridae, genus Paramyxovirus. Mumps virus is sensitive to heat and ultraviolet light.
Epidemiology Mumps is a contagious disease that is spread from person-to-person through contact with respiratory secretions such as saliva from an infected person. Mumps can also be spread by sharing food, sharing drinks, and kissing. The virus can also survive on surfaces and then be spread after contact in a similar manner. A person infected with mumps is contagious from approximately 6 days before the onset of symptoms until about 9 days after symptoms start. The incubation period can be from 14-25 days but is more typically 16-18 days.
Mortality/Morbidity Susceptible children, adolescents, and adults should be vaccinated against mumps, unless vaccination is contraindicated. MMR vaccine is the vaccine of choice for routine administration and should be used in all situations where recipients are also likely to be susceptible to measles, rubella, or both.
RUBELLA Rubella is generally a benign communicable exanthematous disease. Nearly one half of individuals infected with this virus are asymptomatic. Clinical manifestations and severity of illness vary with age. For instance, infection in younger children is characterized by mild constitutional symptoms, rash, and suboccipital adenopathy; conversely, in older children, adolescents, and adults, rubella may be complicated by arthralgia, arthritis, and thrombocytopenic purpura.
Etiology and Epidemiology The disease is caused by a single-stranded RNA rubella virus, which is a member of the Rubivirus genus of the family Togaviridae. Rubella virus is transmitted by the respiratory route. Humans are the only natural hosts. Rubella is a disease that occurs worldwide. The virus tends to peak during the spring in countries with temperate climates.
Mortality/Morbidity The morbidity and mortality rates of rubella disease dropped remarkably since the licensing of live attenuated rubella vaccine in 1969. In contrast to postnatal rubella, which is not a debilitating disease, congenital rubella infection may result in growth delay, learning disability, mental retardation, hearing loss, congenital heart disease, and eye, endocrinologic, and neurologic abnormalities.