Communicable disease
Communicable diseases are illnesses caused by pathogenic biological agents like viruses, bacteria, and parasites that can be spread from one person to another, or from animals to humans, through various routes including air, bodily fluids, insect bites, and contaminated food or water. Common examples include tuberculosis, malaria, HIV, influenza, and hepatitis, and their transmission varies by disease, from airborne droplets (tuberculosis) to mosquito bites (malaria) or sexual contact (HIV). Prevention methods focus on hygiene, vaccination, and vector control to limit their spread.
Infections from pathogens Communicable diseases result from the presence and growth of disease-causing microorganisms (pathogens) in a host.
Transmission: They can spread through direct contact, airborne droplets, contaminated surfaces (fomites), bodily fluids, sexual intercourse, insect vectors (like mosquitoes), or contaminated food and water. .
How They Spread
• Contact: Skin-to-skin contact or contact with bodily fluids. • Airborne: Coughing or sneezing spreads droplets containing pathogens. • Vector-borne: Inoculation of pathogens by insects like mosquitoes. • Vehicle-borne: Contaminated water, food, or soil. • Vertical transmission: From mother to child during pregnancy or childbirth.Prevention
• Vaccination: Protects against some communicable diseases, such as influenza and measles. • Hygiene: Regular handwashing and food preparation practices can prevent infections from food and water. • Vector control: Eliminating mosquito breeding grounds to prevent malaria. • Safe sex practices: To prevent sexually transmitted infections like HIV. • Awareness and reporting: Public health initiatives and reporting of outbreaks are crucial for control.Example of Communicable disease
1 SMALLPOX (VARIOLA)
An acute infectious disease caused by variola virus, and clinically characterized by a sudden onset of fever, headache, backache, vomiting and sometimes convulsions, especially in children. On the third day of fever, a typical rash appears which is centrifugal in distribution and passes through successive stages of macule, papule, vesicle, pustule, and scab with subsequent scarring. Previously, it was one of the greatest killer diseases. In 1967, WHO began an intensified worldwide campaign to eradicate smallpox, based on the technique of surveillance and containment. The last known case of smallpox in India occurred on 24th May 1975. India was declared smallpox free on 5th July 1975. The eradication of smallpox was confirmed in April 1977 by an international commission. The World Health Assembly confirmed the global eradication of smallpox in May 1980. All countries have discontinued routine vaccination against smallpox. However, WHO maintains a reserve stock of smallpox vaccine and vaccination needles – sufficient to protect more than 200 million people, should an emergency arise. .
2. Chickenpox (Varicella)
Chickenpox or varicella is an acute, highly infectious disease caused by varicella-zoster (V-Z) virus. It is characterized by vesicular rash that may be accompanied by fever and malaise. It is worldwide in distribution and occurs in both epidemic and endemic forms. Chickenpox and herpes zoster are now regarded as different host responses to the same aetiological agent. Inoculation of zoster visicle fluid into children produces chickenpox, and children who have recovered from zoster virus related infection are resistant to varicella. .
Varicella-Zoster Immunoglobulin (VZIG)
Varicella-Zoster Immunoglobulin (VZIG) given within72 hours of exposure has been recommended for prevention of chickenpox in exposed susceptible individuals particularlyin immunosuppressed persons. These include (a) susceptible persons receiving immunosuppressive therapy; (b) persons with congenital cellular immunodeficiency; (c) persons with acquired immunodeficiency including HIV/AIDS; (d) susceptible and exposed persons, in particular pregnantwomen; (e) newborns; and (f) premature infants of low birth weight. It has no therapeutic value in established disease. VZIG is given by intramuscular injection in a dose of 12.5 units/kg body weight up to a maximum of 625 units, with a repeat dose in 3 weeks, if a high-risk patient remains exposed. Because VZIG appears to bind the varicella vaccine, the two should not be given concomitantly (4). .
Measles (Rubeola)
An acute highly infectious disease of childhood caused by a specific virus of the group myxoviruses. It is clinically characterized by fever and catarrhal symptoms of the upper respiratory tract (coryza, cough), followed by a typical rash. Measles is associated with high morbidity and mortality in developing countries. Measles occurs only in humans. There is no animal reservoir of infection. .
Rubella (German measles)
Rubella or German measles is an acute childhood infection, usually mild, of short duration (approximately 3 days) and a maculopapular rash. Infection in early pregnancy may result in serious congenital defects, including death of the foetus. The disease is worldwide in distribution and tends to occur in epidemics. In pre-vaccination era epidemics occurred every 5 to 9 years. However, extent and periodically of rubella are highly variable in industrialized and developing countries. Worldwide over 100,000 babies are born with congenital rubella syndrome every year. .
Mumps
An acute infectious disease caused by an RNA virus classified as genus Rubulavirus of the family paramyxoviridae which has a predilection for glandular and nervous tissues. Clinically, the disease is recognized by non-suppurative enlargement and tenderness of one or both the parotid glands. Other organs may also be involved. Constitutional symptoms vary, or may be inapparent. The disease occurs throughout the world. Although morbidity rate tends to be high, mortality rate is negligible. .
In most parts of the world, the annual incidence of mumps in the absence of immunization is in the range of 100-1000 cases/100,000 population with epidemic peak every 2-5 years. Natural infection with this virus is thought to confer lifelong protection (1). .Influenza
Influenza is an acute respiratory tract infection caused by influenza virus, of which there are 4 types-A, B, C and D. All known epidemics are caused by influenza A and B strains. The disease is characterized by sudden onset of chills, malaise, fever, muscular pains and cough. .
Diptheria
Diptheria is an acute bacterial infectious disease caused by toxigenic strains of Corynebacterium diphtheria. Three major clinical types have been described : anterior nasal, faucial and laryngeal; however, the skin, conjunctiva, vulva and other parts of the body may be affected. The bacilli multiply locally, usually in the throat, and elaborate a powerful exotoxin which is responsible for : .
a) the formation of a greyish or yellowish membrane (“false membrane”) commonly over the tonsils, pharynx or larynx (or at the site of implantation), with well-defined edges and the membrane cannot be wiped away; b) marked congestion, oedema or local tissue destruction; c) enlargement of the regional lymph nodes; and d) signs and symptoms of toxaemia.Fatality rate on the average is about 5-10 per cent which has changed little in the past decades in untreated cases, and in children under 5 years of age, and adults over 40 years of age, one out of 5 persons who get diphtheria dies. .
Whooping cough (Pertussis)
An acute infectious disease, usually of young children, caused by B. pertussis. It is clinically characterized by an insidious onset with mild fever and an irritating cough, gradually becoming paroxysmal with the characteristic “whoop” (loud crowing inspiration) often with cyanosis and vomiting. The spectrum of disease varies from severe illness to atypical and mild illness without whoop. The Chinese call it a “Hundred Day Cough”. .
Meningococcal Meningitis
Meningococcal meningitis or cerebrospinal fever is an acute communicable disease caused by N.meningitidis. It usually begins with intense headache, vomiting and stiff neck and progresses to coma within a few hours. The meningitis is part of a septicaemic process. The fatality of typical untreated cases is about 50 per cent. With early diagnosis and treatment, case fatality rates have declined to less that 8-15 per cent. .
Acute Respiratory Infections
Infections of the respiratory tract are perhaps the most common human ailment. While they are a source of discomfort, disability and loss of time for most adults, they are substantial cause of morbidity and mortality in young children and the elderly. Many of these infections run their natural course in older children and in adults without specific treatment and without complications. However, in young infants, small children and in the elderly, or in persons with impaired respiratory tract reserves, it increases the morbidity and mortality rates. .
Acute respiratory infections (ARI) may cause inflammation of the respiratory tract anywhere from nose to alveoli, with a wide range of combination of symptoms and signs. ARI is often classified by clinical syndromes depending on the site of infection and is referred to as ARI of upper (AURI) or lower (ALRI) respiratory tract. The upper respiratory tract infections include common cold, pharyngitis and otitis media. The lower respiratory tract infections include epiglottitis, laryngitis, laryngotracheitis, bronchitis, bronchiolitis and pneumonia. The clinical features include running nose, cough, sore throat, difficult breathing and ear problem. Fever is also common in acute respiratory infections. Most children with these infections have only mild infection, such as cold or cough. However, some children may have pneumonia which is a major cause of death. In less developed countries, measles and whooping cough are important causes of severe respiratory tract infection. .
SEVERE ACUTE RESPIRATORY SYNDROME (SARS)
Severe acute respiratory syndrome (SARS) is a communicable viral disease, caused by a new strain of coronavirus, which differs considerably in genetic structure from previously recognized coronavirus. The most common symptoms in patient progressing to SARS include fever, malaise, chills, headache myalgia, dizziness, cough, sore throat and running nose. In some cases there is rapid deterioration with low oxygen saturation and acute respiratory distress requiring ventilatory support. It is capable of causing death in as many as 10 per cent cases (1).Chest X-ray findings typically begin with a small, unilateral patchy shadowing, and progress over 1-2 days to become bilateral and generalized, with interstitial/confluent infiltration. Adult respiratory distress syndrome has been observed in a number of patients in the end stages.) .
CORONAVIRUS DISEASE-19
Coronavirus disease-2019 (COVID-19) is caused by SARS-CoV-2, a newly emergent coronavirus that was first recognized in Wuhan, China, in December 2019. Genetic sequencing of the virus suggests that it is a betacoronavirus closely linked to SARS virus. It is from the family of single stranded RNA virus (+ss RNA) with a crown like appearance under an electronic microscope, of approximately60-140 nm diameter, contains large widely spread club or petal shaped spikes. Although high temperature decreases the replication of the virus, it can resist the cold temperature. It is sensitive to ultraviolet rays, and is effectively inactivated lipid solvents including ether (75 per cent), ethnol. chlorine-containing disinfectants, peroxyacetic acid and chloroform except for chlorhexidine (1). .
The dynamics of SARS-CoV-2 are currently unknown, but it is speculated that it has an animal origin. .
TUBERCULOSIS
Tuberculosis is a specific infectious disease caused by M. tuberculosis. The disease primarily affects lungs and causes pulmonary tuberculosis. It can also affect intestine, meninges, bones and joints, lymph glands, skin and other tissues of the body. The disease is usually chronic with varying clinical manifestations. The disease also affects animals like cattle; this is known as “bovine tuberculosis” which may sometimes be communicated to man. Pulmonary tuberculosis, the most important form of tuberculosis which affects man, will be considered here. .
POLIOMYELITIS
Poliomyelitis is an acute viral infection caused by an RNA virus. It is primarily an infection of the human alimentary tract but the virus may infect the central nervous system in a very small percentage (about 1 per cent) of cases resulting in varying degrees of paralysis, and possibly death. .
VIRAL HEPATITIS
Viral hepatitis is a term commonly used for several clinically similar yet aetiologically and epidemiologically distinct diseases. It is caused by five different viruses with transmission either through contaminated food or water (hepatitis A and E) or through exposure to blood or body fluids (hepatitis B, C and D). Hepatitis A and hepatitis have been recognized as separate entities since early 1940sand can be diagnosed with specific serological tests. Delta hepatitis is an infection dependent on the hepatitis B virus. It may occur as a coinfection with acute HBV infection or as superinfection of an HBV carrier. .
НЕРАТITIS A
Hepatitis A (formerly known as “infectious” hepatitis or epidemic jaundice) is an acute infectious disease caused by hepatitis A virus (HAV). The disease is heralded by non-specific symptoms such as fever, chills, headache, fatigue, generalized weakness and aches and pains, followed by anorexia, nausea, vomiting, dark urine and jaundice. The disease spectrum is characterized by the occurrence of numerous subclinical or asymptomatic cases. The disease is benign with complete recovery in several weeks. The case rate of icteric cases is less than 0.1 per cent, usually from acute liver failure and mainly affects older adults. Although the disease has, in general, a low mortality patient may be incapacitated for many weeks. .
HЕPАTITIS B
Hepatitis B (formerly known as “serum” hepatitis) is an acute systemic infection with major pathology caused by hepatitis B virus (HBV). HBV infection can be either acute or chronic, and may range from asymptomatic infection or mild disease, to severe, or rarely fulminant hepatitis. Acute hepatitis B is usually a self-limiting disease marked by acute inflammation and hepatocellular necrosis with case fatality rate of 0.5 to 1 per cent. Chronic hepatitis B infection encompasses a spectrum of disease and is defined as persistent HBV infection with or without associated active viral replication and evidence of hepatocellular injury and inflammation. Age is a key factor in determining the risk of chronic infection. Worldwide, the majority of persons with CHB were infected at birth or in early childhood (13).Hepatitis B virus can form a dangerous alliance with delta virus and produce a new form of virulent hepatitis which is considered to be widespread threat for much of the world. .
HEPATITIS C
Hepatitis C is a contagious liver disease that results from infection with the hepatitis C virus. It can range in severity from a mild illness lasting a few weeks to a serious, lifelong illness. It is among the most common virus that infect the liver and it has been shown to be a major cause of parenterally transmitted hepatitis. .
Every year, 1.5 million people are infected with the hepatitis C virus. About 110 million people are HCV antibody positive and 58 million are chronically infected and are at risk of developing liver cirrhosis and/or liver cancer. More than 2,90,000 people died from hepatitis C. .
HEPATITIS D
Hepatitis D is caused by hepatitis D virus that requires HBV for its replication. Hepatitis D cannot occur in the absence of HBV. The coinfection or super infection of HDV with HBV causes a more severe disease than HBV monoinfection. .
HEPATITIS G
Hepatitis G virus HGV was discovered in 1996. The prevalence of this infection is still not known. A few publications provide information on the association of this infection with blood transfusion in India. .
ACUTE DIARRHOEAL DISEASES
Diarrhoea is defined as the passage of loose, liquid or watery stools. These liquid stools are usually passed more than three times a day. However, it is the recent change in consistency and character of stools rather than the number of stools that is more important. The term “diarrhoeal diseases” should be considered only as a convenient expression – not as a nosological or epidemiological entity – for a group of diseases in which the predominant symptom is diarrhoea.
Cholera
Cholera is an acute diarrhoeal disease caused by V. Cholorae O1 (classical or El Tor) and O139. It is now commonly due to the El Tor biotype and O139. It is now commonly due to the El Tor biotype and O139. Cases range from symptomless to severe infections. The majority of infections are mild or asymptomatic. Typical cases are characterized by the sudden onset of profuse, effortless, watery diarrhea followed by vomiting, rapid dehydration, muscular cramps and suppression of urine. Unless there is rapid replacement of fluid and electrolytes, the case fatality may be as high as 30 to 40 per cent.
Typhoid Fever
Typhoid fever is the result of systemic infection mainly by S.typhi found only in man. The disease is clinically characterized by a typical continuous fever for 3 to 4 weeks, relative bradycardia with involvement of lymphoid tissues and considerable constitutional symptoms. The term “enteric fever” includes both typhoid and paratyphoid fevers. The disease may occur sporadically, epidemically or endemically.
Food Poisioning
Food poisoning is an acute gastroenteritis caused by ingestion of food or drink contaminated with eith living bacteria or their toxins or inorganic chemical substance and poisons derived from plants and animals. The condition is characterized by : a) history of ingestion of a common food b) attack of many persons at the same time, and c) similarity of signs and symptoms in the majority of cases.
Amoebiasis
The term “amoebiasis” has been defined by WHO as the condition of harbouring the protozoan parasite Entamoeba histolytica with or without clinical manifestations. The symptomatic disease occurs in less than 10 per cent of infected individuals. The symptomatic group has beenfurther subdivided into intestinal and extraintestinal amoebiasis. Only a small percentage of those having intestinal infection will develop invasive amoebiasis. The intestinal disease varies from mild abdominal discomfort and diarrhoea to acute fulminating dysentery. Extraintestinal amoebiasis includes involvement of liver (liver abscess), lungs, brain, spleen, skin, etc. Amoebiasis is potentially lethal disease. It carries substantial morbidity and mortality.
Soil-Transmitted Helminthiasis
Soil-transmitted helminth (STHs) infections refer to a group of parasitic diseases in humans caused by intestinal roundworms (ascariasis), hookworms (Necator americanus and Ancylostoma duodenale) and whipworm (Trichuris trichiura). They are the most common infections worldwide. More than 1.5 billion people or about 24 per cent of the world’s population are infected. Infections are widely distributed in tropical and subtrophical areas, with the greatest numbers occurring in sub-Saharan Africa, the Americas, China and East Asia. Over 267 million preschool children and over 568 million school-age children and 250 million girls and adult women live in areas where these parasites are intensively transmitted and are in need of treatment and preventive interventions.
Whipworm
Whipworm is the third most common soil-transmitted helminthiasis in the humans. According to current estimate, nearly 440 million people are infected, and majority of cases are children 4-10 years age. Heavy infection could lead to acute symptoms such as diarrhea and anaemia, and chronic symptoms such as growth retardation and impaired cognitive development. It is quite common in United States, South-East Asia, to a lesser equatorial Africa, Central and South America.
The Dengue Syndrome
Dengue viruses are arboviruses capable of infecting humans, and causing disease. These infections may be asymptomatic or may lead to (a) “classical” dengue fever, or (b) dengue haemorrhagic fever without shock, or (c) dengue haemorrhagic fever with shock.
Dengue fever is a self-limiting disease and represents the majority of cases of dengue infection. A prevalence of Aedes aegypti and Aedes albopictus together with the circulation of dengue virus of more than one type in any particular area tends to be associated with outbreaks of DHF/DSS.
. Malaria
Malaria is a protozoal disease caused by infection with parasites of the genus Plasmodium and transmitted to man by certain species of infected female. Anopheline mosquito. A typical attack comprises three distinct stages : cold stage, hot stage and sweating stage. The clinical features of malaria vary from mild to severe, and complicated, according to the species of parasite present, the patient’s state of immunity, the intensity of the infection and also the presence of concomitant conditions such as malnutrition or other diseases. The febrile paroxysms occur with definite intermittent periodicity repeating every third or fourth day depending upon the species of the parasite involved.
Lymphatic Filariasis
The term “lymphatic filariasis” covers infection with three closely related nematode worms – W. bancrofti, B. malayi and B. timori. All three infections are transmitted to man by the bites of infective mosquitoes. All three parasites have basically similar life cycles in man-adult worms living in lymphatic vessels whilst their offspring, the microfilariae circulate in peripheral blood and are available to infect mosquito vectors when they come to feed (1). The disease manifestations range from none to both acute and chronic manifestations such as lymphangitis, lymphadenitis, elephantiasis of genitals, legs and arms or as a hypersensitivity state such as tropical pulmonary eosinophilia or as an atypical form such as filarial arthritis. Though not fatal, the disease is responsible for considerable suffering, deformity and disability.
Rabies
Rabies, also known as hydrophobia is an acute, highly fatal viral disease of the central nervous system, caused by Lyssavirus type 1. It is primarily a zoonotic disease of warm-blooded animals, particularly carnivorous such as dogs, cats, jackals and wolves. It is transmitted to man usually by bites or licks of rabid animals. Classical hydrophobia is clinically characterized by a long and variable incubation period, a short period of illness due to encephalomyelitis ending in death, despite intensive care. It is the only communicable disease of man that is always fatal.
Taeniasis
A group of cestode infections which are important zoonotic diseases. Three parasites of importance in taeniasis are Taenia saginata, T. solium and T. asiatica. These are classified as “cyclo-zoonoses” because they require more than one vertebrate host species (but no invertebrate host) to complete their developmental cycles. Humans can become infected with T. saginata or T. asiatica when they consume beef meat or pig liver tissue, respectively, which has not been adequately cooked. Infection with the T. solium tapeworm occurs when humans eat raw or undercooked, infected pork. Tapeworm eggs pass with the faeces and are infective for pigs. Infection in humans with the T. Solium causes few clinical symptoms. However, infection with the larval parasite in the tissue (human cysticercosis) can result in devastating effect on human health. The larvae may develop in the muscle, skin, eyes and the central nervous system (neurocysticercosis). Neurocysticercosis is the most frequent preventable cause of epilepsy worldwide, and is estimated to cause 30 per cent of all epilepsy cases in countries where the parasite is endemic.
Cysticercosis mainly affects the health and livelihood of communities in developing countries of Africa, Asia and Latin America. In 2010, the WHO added T. solium cysticercosis to the list of major Neglected Tropical Diseases. In 2015, the WHO Foodborne Disease Burden Epidemiology Reference Group identified T. solium as a leading cause of deaths from food-borne diseases resulting in a considerable total of 2.8 million DALYs lost and an estimated 2.56-8.30 million symptomatic and asymptomatic neurocysticercosis.
Trachoma
Trachoma is a chronic infectious disease of the conjunctiva and cornea, caused by Chlamydia trachomatis, but other pathogenic microorganisms often contribute to the disease. Trachoma inflammation may undergo spontaneous resolution or may progress to conjuctival scarring which can cause inward deviation of eyelashes (trichiasis) or of the lid margin (entropion). The abrasion of the cornea by eyelashes frequently results in corneal ulceration, followed by scarring and visual loss. .
From the public health point of view, trachoma is classified as blinding and non-blinding. A community with blinding trachoma can be recognized by the presence of persons with lesions such as entropion, trichiasis and corneal ulcers. It is the blinding trachoma that requires urgent control measures. Non-blinding trachoma often becomes blinding trachoma when other ocular pathogens interact synergistically and enhance the risk of damage to eye sight. .
Tetanus
An acute disease induced by the exotoxin of Clostridium tetani and clinically characterized by muscular rigidity which persists throughout illness punctuated by painful paroxysmal spasms of the voluntary muscles, especially the masseters (trismus or “lock-jaw”), the facial muscles (risus sardonicus), the muscles of the back and neck (opisthotonos), and those of the lower limbs and abdomen. The mortality tends to be very high, varying from 40 to 80 per cent. .
Leprosy
Leprosy (Hansen’s disease) is a chronic infectious disease caused by M. leprae. It affects mainly the peripheral nerves. It also affects the skin, muscles, eyes, bones, testes and internal organs. The disease manifests itself in two polar forms, namely the lepromatous leprosy and tuberculoid leprosy, lying at the two ends of a long spectrum of the disease. Between these two polar types occur the borderline and indeterminate forms depending upon the host response to infection.
Sexually transmitted diseases
The sexually transmitted diseases (STD) are a group of communicable diseases that are transmitted predominantly by sexual contact and caused by a wide range of bacterial, viral, protozoal and fungal agents and ectoparasites. During the past few decades, STDs have undergone a dramatic transformation (1). First, the change in name from venereal diseases (V.D.) to sexually transmitted diseases (STD) indicates this transformation. The list of pathogens which are sexually transmissible has expanded from the 5 “classical” venereal diseases (syphilis, gonorrhoea,chancroid, lymphogranuloma venereum and donovanosis) to include more than 20 agents. Secondly, attention is now given not only to specific diseases, but also to clinical syndromes associated with STDs. Most of the recently recognized STDs are now referred to as second generation STDs. AIDS, the most recently recognized, is a totally new disease.
33. AIDS
AIDS, the acquired immune-deficiency syndrome (sometimes called “slim disease”) is a fatal illness caused by a retrovirus known as the human immune-deficiency virus (HIV) which breaks down the body’s immune system, leaving the victim vulnerable to a host of life-threatening opportunistic infections, neurological disorders, or unusual malignancies. Among the special features of HIV infection are that once infected, it is probable that a person will be infected for life. Strictly speaking, the term AIDS refers only to the last stage of the HIV infection. AIDS can be called our modern pandemic, affecting both industrialized and developing countries.
(h) AIDS:The problem of AIDS is stable. It is estimated that by the end of year 2021 there were about 2.4 million HIV positive cases in the country. • Others: Kala-azar, meningitis, viral hepatitis, Japanese encephalitis, dengue fever, enteric fever and helminthic infestations are among the other important communicable disease problems in India. The tragedy is that most of these diseases can be either easily prevented or treated with minimum input of resources. In fact most of the developed countries of the world have overcome many of these problems by such measures as manipulation of environment, practice of preventive medicine and improvement of standards of living.