In this article we will discuss about the methods and strategies applied for controlling the following infectious diseases: 1. Malaria 2. Tuberculosis 3. AIDS (HIV) 3. Cholera 4. Poliomyelitis 5. Viral Hepatitis 6. Lymphatic Filariasis 7. Leishmaniasis.
How to Control Malaria?
Malaria is a protozoan disease caused by infection with parasites of the genus Plasmodium and transmitted to man by certain species of infected female Anopheline mosquito. Malaria is one of the oldest recorded diseases in the world.
In 18th century, people in Italy associated malaria with “bad air”. In 1880, Lave ran, a French army surgeon discovered malaria parasite in Algiers. The main credit goes to Sir Ronald Ross who while working in Secundrabed (Andhra Pradesh) in 1887 discovered transmission of malaria by Anopheline mosquito.
Malaria is one of the most widespread diseases of the world occurring between 60°N and 40°S. Endemic malaria, no longer occurs in temperate zone i.e. whole of Europe, whole of the former USSR, several countries of the near East, USA, most of the Caribbean, large areas of the northern and southern parts of South America, Australia and large parts of China.
An estimate of the problem of malaria in India made in 1953 furnishes following information:
1. An annual incidence of 75 million cases
2. An annual incidence of 8 lakh deaths directly due to malaria.
3. 10.8% of cases of diagnosed malaria
4. A spleen rate of 15.7%
5. A child parasite rate of 3.8%
6. An infant parasite rate of 1.6%
According to World Health Organization, malaria afflicts about 500 million people annually the world over; 90 percent of the cases occur in Africa alone, and the rest mainly in India, Brazil, Sri Lanka, Afghanistan, Thailand, Vietnam, and Colombia. The disease claims about 2.7 million lives annually, including an estimated one million African children under five.
The magnitude of the problem was great. As a result National Malaria Control Programme (NMCP) and National Malaria Eradication Programme (NMEP) were initiated in 1953 and 1958 respectively. In 1961, there were only 40,000 cases of mal aria in the country. However, massive resurgence of malaria occurred in India in mid 1970s.
In 1976 the incidence of malaria rose to a peak of 6.4 million cases with 59 deaths. A “Modified plan of Operation” was launched in 1977. As a result, the number of malaria cases dropped to 2.1 million by 1984. However, epidemiological situation has not shown any improvement since then. The entire population of India (95.9%) is now deemed to be under malaria risk.
Malaria is usually accompanied by anemia and enlargement of the spleen.
Hyperpyrexia (persistent high temperature), can cause febrile fits and brain damage. Occasionally, destruction of RBC can lead to hypoxia (reduced oxygen supply to the tissues). Malaria can also seriously jeopardize the outcome of pregnancy, the chances of abortion, low birth weight, still births and complication during delivery are enhanced.
Several factors including environmental factors, agent factors and host factors are responsible for the spread of malaria.
India’s geographic position and climatic conditions had been, for long favourable to the transmission of malaria.
Malaria is a seasonal disease. In most parts of India, the maximum prevalence is from July to November.
Temperature affects the life cycle of malarial parasite. The optimum temperature for the development of parasite in insect vector is 20° C to 30° C. The parasite ceases to develop if the temperature is below 16° C. Temperature higher than 30° C is lethal to the parasite.
A relative humidity of 60% is considered necessary for mosquitoes to live their normal span of life. If the humidity is low, mosquitoes do not live long.
Rain increases the atmospheric humidity which is necessary for the survival of mosquitoes. However, heavy rain may have an adverse effect in flushing out the breeding places. The relationship between rainfall and mosquito breeding is of fundamental importance.
As a rule Anopehlines are not found at altitudes above 2,000-2,500 metres, due to unfavourable climatic conditions.
(f) Manmade Malaria:
Burrow pits, garden pools, irrigation channels and engineering projects have led to the breeding of mosquitoes and an increase in malaria. Malaria consequent on such undertakings is called man made malaria.
Malaria in man is called by four distinct species of the malaria parasite – Plasmodium vivax, P. falciparum. P. malaria and P. ovale. P. vivax has the widest geographic distribution throughout the world. In India, 70 percent infections are reported to be due to P. vivax, 25 to 30 percent due to P. falciparum and 4 to 8 percent due to mixed infection. P. malariae is responsible for less than 1 percent infection. P. ovale is the rare parasite of man mostly confined to tropical Africa. It has also been reported in Viet nam. The severity of malaria is related to the species of the parasite.
iii. Host Factors:
The main variables of the human element that have an influence on malaria epidemiology include the following:
Malaria affect all ages. Newborn infants have considerable resistance to infection with P. falciparum. This has been attributed to high concentration of fetal haemoglobin.
Males are more susceptible to malaria than females. Females in India are better clothed than males.
Individuals with AS haemoglobin (sickle cell trait) have a milder illness with falciparum infection than do those with normal (AA) haemoglobin.
Pregnancy increases the risk of malaria in women. Malaria during pregnancy may cause the intrauterine death of the fetus.
(e) Socio-Economic Development:
It is generally accepted that malaria has disappeared from most developed countries as a result of socioeconomic development.
Ill-ventilated and ill-lighted houses provide ideal indoor resting places for mosquitoes. Malaria is acquired in most cases by mosquito bites within the houses.
(g) Population Mobility:
Labourers, nomads and wandering tribes are outstanding examples of internal migration. Some of them may import malarial parasites in their blood and reintroduce malaria into areas where malaria has been controlled or eliminated. Imported malaria has become a public health problem in Europe, North America and other temperate parts of the world owing to increased air travel, tourism and migration.
Malaria is predominantly a rural disease and is closely related to agricultural practices.
(i) Human Habits:
Habits such as sleeping outdoors, nomadism, not using measures of personal protection influence man-vector contact and obviously the choice of control measures.
The epidemic of malaria is influenced by the immune status of the population. People living in endemic areas exposed continually to malaria develop considerable degree of resistance. Immunity to malaria is acquired only after repeated exposures after several years.
Out of about 45 species of anopheline mosquitoes in India only a few are regarded as vectors of primary importance. These are Anopheles culcifacies, A. fluviatilis, A. stephensi, A. minimus, A. philippinensis, A. sundiacus and A. maculatus. The vectors of major importance are A. culcifacies in rural areas and A. stephensi in urban areas.
1) Vector Transmission:
Malaria is transmitted by the bite of certain species of infected, female, anopheline mosquitoes. A single infected Vector during her life time may infect several persons. The mosquito is not infective unless the sporozoites are present in the salivary glands.
2) Direct Transmission:
Malaria may be induced accidentally by hypodermic intramuscular and intravenous injections of blood or plasma e.g. blood transfusion, malaria in drug addicts. Blood transfusion poses a problem because the parasites keep their infective activity during at least 14 days in blood bottles stored at -4°C.
3) Congenital Malaria:
Congenital infection of the new born from an infected mother may also occur but it is comparatively rare.
Malaria varies with the type of parasite or vector involved, the value of resistance and eco-epidemiological considerations:
a. Tribal Malaria:
Generally prevalent in the tribal areas of deep forests, forest-fringes (subtype I) and surrounding ecologically disturbed areas (subtype II), it poses a management problem due to poor health infrastructure and inadequate drugs. P falciparum is predominant with multiple drug resistance; deaths are common.
Subtype II regions are prone to epidemics due to population migrations. According to NMEP data, tribal areas, with about eight percent of the total Indian population, account for 39 percent of all malaria cases and 68 percent of P falciparum cases in the country.
b. Rural Malaria:
Moderately endemic in the irrigated areas of arid and semi-arid plains (subtype I), rural malaria has a predominance of P vivax. Widespread vector resistance to multiple insecticides and localized parasite resistance to chloroquine pose problems for the moderately developed health infrastructure.
Poor irrigation, waterlogging, seepages from canals and poor drainage systems are responsible for the increase of malaria. The rural areas around the Upper Krishna irrigation project in Karnataka, Sardar Sarover Dam in Gujarat and the Indira Gandhi Canal in Rajasthan have witnessed outbreaks recently.
c. Urban Malaria:
Towns and cities (subtype II) are moderately endemic with P vivax predominance and focal incidence of P falciparum. Sporadic epidemics occur, especially around construction projects. The main vectors are A stephansi and A culicifacies. Sub-urban and per-urban areas (subtype II), with unplanned settlements, slums and poor sanitary conditions are prone to epidemics and deaths due to P faciparum infection.
d. Industrial Malaria:
Development projects are highly prone to malaria epidemics resulting from drug resistant parasites, one or more vectors refractory to transmission control and limited health infrastructure. NMEP data clearly shows that the construction of the Mirzapur thermal power project, Uttar Pradesh, saw a five-fold increase in malaria incidence in the district in 1980. The Mathura oil refinery and the National Thermal Power Corporation unit in Dadri also contributed to the rise of malaria incidence in UP.
e. Border Malaria:
Mainly caused by migrations across International borders, this type cuts across all epidemiological boundaries and often contributes new and drug resistant parasite strains. Migration even within the country complicates the epidemiological classification. Kondrashir, a WHO malaria expert, estimated in 1991 that about one- sixth of India’s population moves annually during the transmission season from non- malarious areas to malarious areas and vice versa.
A country-wide review of malaria control strategies was undertaken in 1995, following which a Malaria Action Programme (MAP) was launched, as a commitment to WHO Global Malaria Control Strategy (1992). The new strategy emphasizes decentralization, epidemiological approaches in malaria control, community participation, management information systems and health education among other things.
Under the proposed new strategy, the financial, technical and administrative responsibilities will be shared by major establishments in the private and public sectors. Health impact assessment has been made an integral part of the environmental impact assessment of all developmental projects.
Malaria research has several aspects- developing new drugs, vaccines, simple diagnostic methods, insecticides and larvicides, methods of sterilizing mosquitoes, epidemiological and entomological studies, host parasite interactions, immunology of the disease and finally ecology.
Efforts have been recently made to control mosquito breeding by spraying larvicidal microbes. The fish Gambusia affinis popularly known as mosquito fish has been used throughout the tropical world to control malaria spreading mosquitoes. Four other species of the fish Daneo rario, Aplocheilus panchax, Oryzias melastigma and Tilapia mossambica are also known to feed on mosquito larvae.
Impregnated bednets are being increasingly recommended for malaria control following encouraging results in Orissa and the north-east. These bednets are impregnated twice a year with synthetic pyrethroids offering effective protection for six- eight months from mosquitoes) bed bugs and headlice.
Among the new drugs waiting to be introduced in the market is a Chinese herb derivative Artemisia accua. Artemisin (the raw material) has been identified as a potent antimalarial drug. It has cured multi-drug resistant malaria cases in Viet nam, Thailand and Combodia.
In India clinical trials of Arteether, a derivative developed by Central Drug Research Institute, Lucknow are currently underway. Indigenous production and sale of mafloquin was cleared by Govt, of India in March, 1996.
There are three major stages in the life cycle of the parasite which are targets of vaccine development.
i. A vaccine based on sporozoites is designed to prevent infection.
ii. Vaccines based on the asexual blood stages of the parasite (mesozoites) will not prevent infection) but can reduce or eliminate parasites in the blood.
iii. Vaccines directed at the sexual stages of the parasite (gametocytes) aim to interfere with the ability of the parasite to infect mosquitoes and thereby prevent transmission of the disease. A vaccine developed by a group of Australian researchers is undergoing trials since 1994 in USA and Africa.
There are no magic bullets to beat malaria as yet. Setting aside eradication, better public health management practices, strong primary health care infrastructure, emphasis on preventive measures and community participation have the potential to reduce malaria incidence and make the WHO’s dream of a one-fifth reduction in malaria incidence by 2000 A.D. in at least 75 percent of the affected countries- a reality.
Tuberculosis is a specific infectious disease caused by Myobacterium tuberculosis. The pathogen primarily affects lungs and causes pulmonary tuberculosis. It can also infect intestine, meninges, bones, joints, lymph gland, skin and other tissues of the body. The disease also affects animals and is called as bovine tuberculosis. Tuberculosis remains a worldwide public health problem.
There are 15-20 million cases of infectious tuberculosis in the world. Eight million new victims and 2.9 million deaths are known to occur every year. The disease is credited with killing over one million women and 1,70,000 children every year. WHO has declared TB as a global emergency.
The incidence of TB rose by 12 percent in the US between 1986-1991; Italy reported a 28 percent jump between 1988 and 1990 and Switzerland a 33 percent increase from 1986 to 1990. Experts have attributed this upward trend to changes in the social structure of the cities, the HIV epidemic and a failure in certain regions to improve public health treatment programmes.
The problem has assumed a far more fearsome aspect in developing countries. Asian countries are the home to majority of the world’s TB infected population. In India, 30 percent male and 35 percent female population suffer from TB. According to National Tuberculosis Institute, Bangalore 30 percent of population is infected in contrast to 2-3 percent in developed countries.
A few factors viz.- agent factors, host factors and social factors can be discussed to understand the natural history of TB.
It is caused by a facultative intracellular parasite Myobacterium tuberculosis. It is readily ingested by phagocytes and is resistant to intracellular killing.
The most common source of infection is human. The bovine source of infection is usually the infected milk. Patients are infective as long as they remain untreated. Effective antimicrobial treatment reduces infectivity by 90 percent within 48 hours.
Tuberculosis affects all ages. It is more prevalent in males than females. It is not a hereditary disease but inherited susceptibility is an important risk factor. Man has no inherited immunity against tuberculosis. It is acquired as a result of natural infection or BCG vaccination.
Tuberculosis has been described as a barometer of social welfare. Social factors include many non-medical factors such as poor quality of life, poor housing and overcrowding, population explosion, malnutrition, lack of education, large families, early marriages, lack of awareness of causes of illness etc. In most cases, bacteria attacks the lungs. Pulmonary TB destroys the lung tissue, rupturing blood vessels in the process. Victims are virtually consumed by the disease.
Tuberculosis is transmitted mainly by droplet infection and droplet nuclei generated by sputum positive patients with pulmonary tuberculosis. The frequency and vigour of cough and the ventilation of the environment influence transmission of infection.
According to WHO, “tuberculosis control” is said to be achieved when the prevalence of natural infection in the age group 0-14 years is of the order of 1 percent. At present, this is about 40 percent in India.
The control measures should consists of:
i. Curative component,
ii. Preventive component
Curative component includes case finding and chemotherapy whereas preventive component includes vaccination. The first step in tuberculosis control is early detection of sputum positive cases, sociological studies on pulmonary tuberculosis and mass miniature radiographic examination. Case finding should follow chemotherapy.
Thirteen drugs are now available, active against M tuberculosis of which six are considered to be essential. They include rifampicin (RMP), 1 NH streptomycin, pyrazinamide, ethambutol and thioacetazone.
Ever since Koch discovered M. tuberculosis, attempts have been made to prepare a prophylactic vaccine against tuberculosis. After a continuous series of experiments two fresh scientists’ calmette and Guerin were able to raise a strain known as Bacille Calmette Guverin or BCG that was avirulent for man. BCG was accepted as a safe preventive measure in 1948.
Today BCG vaccination is a fundamental component of a national tuberculosis programme. It is a part of WHO Expanded Programme on Immunization. It is badly needed by the developing countries where tuberculosis is still a major health problem.
The National Tuberculosis Programme was initiated in 1962. The long term goal of NTP is “to reduce the problem of tuberculosis in the community sufficiently quickly to the level where it ceases to be a public health problem”. The backbone of National Tuberculosis programme is the District Tuberculosis programme (DTP). It was evolved by the National Tuberculosis Institute, Bangalore and was accepted by Govt, of India for implementation in 1962.
The District Tuberculosis Programme consists of one District Tuberculosis Centre (DTC) and on an average 50 peripheral health centers. To implement the programme, the Govt, has posted a specially trained team into function.
The team includes:
1. District Tuberculosis officer
2. Laboratory technician
3. Treatment Organizer
4. X-ray technician
5. Non-medical team leader
6. Statistical assistant
The programme works under the ambit of the District Health Organization.
Despite effective case finding and therapeutic tools and declined mortality and morbidity in some countries, tuberculosis still remains to be a serious communicable disease worldwide. The chronic nature of the disease, the ability of the tubercle bacilli to remain alive in the human body for years, the concentration of the disease in the older age groups, the increased expectation of life, high prevalence infection rates in some countries, the relatively high reactivation rate, the emergence of drug resistant strains, association of tuberculosis and HIV infection and above all, the perpetuation of the “non-specific determinations” of the disease in the third world countries impede the rapid conquest of the disease.
AIDS, the acquired immuno-deficiency syndrome (sometimes called “Slim disease”) is a newly described usually fatal illness caused by a retrovirus known as the human immuno-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. Strictly speaking, the term AIDS refers only to the last stage of HIV infection. It can be called as modern pandemic, affecting both industrialized and developing countries.
HIV has infected millions of women, men and children worldwide. According to an estimate of WHO, there were 2.5 million adult full blown AID cases recorded throughout the world in 1993. AIDS was first recognized in USA in 1981, earlier cases were found by retrospective analysis to have occurred in 1978 in USA and in late 1970s in equatorial Africa.
An explosion of HIV has recently occurred in South- East Asia, particularly in Thailand, Burma and India. HIV/AIDS is now known to occur in countries such a Paraguay, Greenland and Pacific Island nations of Fiji, Papua New Guinea and Samoa.
i. Agent Factors:
In May 1986, the International Committee on the Taxonomy named the AIDS causing virus as human immunodeficiency virus. It is 1/10,000th of mm in diameter. It is a protein capsule containing two short strands of genetic material (RNA) and a few enzymes. The virus uses human cells to perpetuate itself.
The virus replicates in actively dividing T4 lymphocytes and like other retroviruses can remain in a latent state in lymphoid cells that can be activated. The virus has the unique ability to destroy human T4 helper cells, a subset of the human T4 lymphocytes. The virus can spread throughout the body. It can pass through the blood-borne barrier and can destroy some brain cells. HIV mutates rapidly. There are two types of HIV-the most common HIV-I and a more recently recognized HIV-2.
The virus has been found in greatest concentration in blood, semen and CSF. However, concentrations have been detected in tears, saliva, breast-milk, and urine, cervical and vaginal secretions. To date only blood and semen have been conclusively shown to transmit the virus.
ii. Host Factors:
Age, sex and immunological status of the host are important host factors. Most cases of infection occur in sexually active persons between the age group of 20-49 years. Children under 15 make up less than 3 percent of cases.
In North America, Europe and Australia, about 70 percent of cases are homosexual or bisexual man. Multiple sexual partners, anal intercourse and male homosexuality increase the risk of infection. Higher rate of HIV infection is found in prostitutes. The immune system disorders associated with HIV infection are considered to occur primarily from the gradual depletion of a specialized group of white blood cells (lymphocytes) called T-helper and T-4 cells.
Mode of Transmission:
The causative virus is transmitted from person to person, most frequently through sexual activity or blood transfusion.
i. Sexual Transmission:
AIDS is first and foremost a sexually transmitted disease. Any vaginal, anal or oral sex can spread AIDS. Every single act of unprotected intercourse with an HIV infected person exposes the uninfected partner to the risk of infection. Anal intercourse carries a higher risk of transmission than vaginal intercourse.
ii. Blood Contact:
AIDS is also transmitted by contaminated blood-transfusion of whole blood cells, platelets and factors VIII and IX derived from human transfusion of infected blood is estimated to be 95%. Needle sharing by drug users is a major cause of AIDS transmission.
iii. Maternal-Foetal Transmission:
HIV may pass from the infected mother to her foetus, through placenta or by breast feeding. Risks are higher if the mother is newly infected or if she has already developed AIDS.
There is no evidence that HIV is transmitted through mosquitoes or any other insects, casual social contact with infected persons even within households or by food or water. There is no evidence of spread to health case workers in their professional contact with people with AIDS.
There are three basic approaches to the control of AIDS:
Until a vaccine or cure for AIDS is found, the only means at present available is health education on avoiding indiscriminate sex, and using condoms. One should also avoid the use of shared razors and toothbrushes) needles and syringes. Infected women should avoid becoming pregnant. All mass media channels should be involved in educating the people on AIDS, its nature, transmission and prevention.
ii. Prevention of Blood-Borne HIV Transmission:
People in high risk groups should be asked to refrain from donating blood, body organs, sperm or other tissues. Blood should be screened for HIV] and HIV2 before transfusion. Strict sterilization practices should be ensured in hospitals and clinics. One should avoid injections unless they are absolutely necessary.
iii. Specific Prophylaxis:
At present there is no vaccine or cure for treatment of HIV infection/AIDS. Antiviral chemotherapy with the chemical compound Zidovudine (AZT) while not a cure, has proved to be useful in prolonging the life of severely ill patients. The AZT, however, neither restores the immune system, nor does in destroy the HIV virus already installed in cells.
iv. Primary Health Care:
AIDS touches all aspects of primary health case, including mother child health, family planning and education, it is important therefore, that AIDS control programmes are not developed in isolation. Integration into countries primary health care system is essential.
The WHO has launched a “Global Programme on AIDS” on Feb. 1, 1987 to provide global leadership and to support the development of National AIDS programme.
Cholera is both an epidemic and endemic disease. The 7th pandemic began in 1961 and today it involves more than 92 countries in Asia, Africa and Europe. Global situation shows definite downward trend of reported cases.
Cholera has been present in India since antiquity. In the history of cholera, four phases have been described.
a) First phase (prior to 1817) – the disease was confined to the east.
b) Second period (1819 – 1923) – six pandemics were described, out of which five originated from India.
c) Third period (1923-1960) – the disease retreated from Europe and came to be known as “Asiatic Cholera’.
d) Fourth period (1961-todate) – it started off as the famous 7th pandemic. After spreading to Hong-Kong and Philippines, it moved steadily north and west ward and reached India in 1964. Then it spread to the Middle East, and North, East and West Africa, Israel, Italy and Portugal. Cases have also occurred in Australia, New Zealand. USA and other developed countries but the disease could not establish itself in these countries. The 7th pandemic is still continuing.
The geographical distribution of cholera in India, keeps on changing. West Bengal is no more a “home of cholera”, now. Andaman and Nicobar Islands were infected for the first time in 1966, and the desert areas of Rajasthan in 1969. Currently the large endemic foci of cholera are found in Maharashtra, Tamil Nadu, Karnataka, Delhi and Kerala. These states account for about 80 percent of reported incidences in the country.
i. Agent Factors:
Cholera is caused by Vibrio cholerae 0 group 1, two biotypes – classical and El Tor vibrios are further divided into three serological types namely Inaba, Ogawa and Hikojima.
ii. Host Factors:
Cholera affects all ages and both sexes. In endemic areas, attack rate is highest in children. Mass population movement’s viz. pilgrimages, fairs, and festivals result in increased risk of exposure to infection. The incidence of cholera tends to be the highest in the lower socio-economic groups and this is attributable to poor hygiene.
iii. Environmental Factors:
Vibrio transmission is readily possible in a community with poor environmental sanitation. Important environmental factors are contaminated water and food. Flies may carry V. cholerae. Numerous social factors have also been found responsible for endemicity of cholera in India. These comprise certain human habits favouring water and soil pollution, low standards of personal hygiene, lack of education and poor quality of life.
Transmission occurs from man to man via faecally contaminated water, contaminated food and drinks and the direct contact.
The main symptom of cholera is diarrhea. According to current concepts, the cholera vibrio gets through the mucus which overlies the intestinal epithelium. It probably secretes mucinase which helps it to move rapidly through the mucus. Then it gets adhered to the intestinal epithelial cells with the help of a probable adhesence factor. After adhering to mucosa, the pathogen produces the enterotoxin.
The enterio- toxin consists of two parts – the light or L-toxin and the heavy or H-toxin. The L-toxin combines with substances in the epithelial cell membrane called gangliosides. The binding is irreversible. The mode of action of H-toxin is not fully clear. What we know is that H-toxin activates adenyl cyclase in the intestinal epithelial cells.
The activated adenyl cyclase causes a rise in another substance called 3,5-adenosine monophosphate better known as cyclic AMP or C-AMP provides energy which divides fluid and ions into the lumen of the intestine. The increase in the fluid is the cause of diarrhoea and not the increased peristalsis. There is no evidence that V. cholerae invades any tissue, nor the entero-toxin to have any direct effect on any organ other than the small intestine.
WHO (1980) has proposed “guidelines for cholera control”. These include- verification of the diagnosis, notification, early case finding, and establishment of treatment centers, rehydration therapy (oral rehydration and intravenous rehydration), adjuncts to therapy, epidemiological investigations, sanitation measures, chemoprophylaxis, vaccination and health education programme.
Poliomyelitis is an acute viral infection caused by a RNA virus. It is primarily an infection of the human alimentary tract but the virus may infect the central nervous system in about 1 percent of cases resulting in varying degrees of paralysis and possibly death. The extensive use of polio vaccines since 1954 has virtually eliminated the disease in developed countries.
However, polio continues to be a serious health problem in India. The first epidemic of polio was reported in and around Bombay City in 1949. Since then, more epidemics have occurred at various times in Andhra Pradesh, Uttar Pradesh, Gujarat, Maharashtra, Rajasthan, Tamil Nadu and Delhi. More recently widespread epidemics have occurred in 1981 and 1987, despite the fact that a national immunization programme (EPI) has been in operation since 1978.
Poliomyelitis can occur sporadically, endemically or epidemically.
i. Agent Factors:
The causative agent is the poliovirus which has three serotypes 1,2 and 3. Most outbreaks of paralytic polio are due to type-1 virus. It can survive for long periods in the external environment. In a cold environment, it can live in water for 4 months and in faeces for six months.
ii. Host Factors:
In India, polio is essentially a disease of infancy and childhood. About 50 percent of cases are reported in infancy. The most vulnerably age is between 6 months and 3 years. Sex differences have been noted in the ratio of 3 males to 1 female.
iii. Environmental Factors:
Polio is more likely to occur during the rainy season. Approximately 60 percent of cases recorded in India were June to September. The environmental sources of infection are contaminated water, food and flies. Polio virus survives for a long time in cold environment. Overcrowding and poor sanitation provide opportunities for exposure to infection.
Main route of infection is faecal-oral route. The infection may spread directly through contaminated fingers where hygiene is poor, or indirectly through contaminated water, milk, foods etc. Droplet infection may occur in the acute phase of disease when the virus occurs in the throat. Incubation period is usually 7 to 14 days.
Immunization is the only effective means of preventing poliomyelitis. It is essential to immunize all infants by 6 months of age to protect them against polio.
Two types of vaccines are used throughout the world:
(i) Inactivated (SALK) Polio Vaccine (IPV)
(i) Inactivated (SALK) Polio Vaccine:
This vaccine contains all three types of poliovirus, inactivated by formalin. The initial course of immunization consists of four inoculations. IPV induces humoral antibodies (lgM, IgG and IgA) but does not induce intestinal or local immunity. Thus it gives protection from paralysis but offers nothing because the wild viruses can still multiply in the gut and be a source of infection for others. This is a major drawback of IPV. However, it is safe to administer as it does not contain live virus.
OPV was described by Sabin in 1957. It contains live attenuated cell cultures. Ideally each virus type should be given separately as monovalent vaccine, but for administrative convenience, it is given as trivalent vaccine.
The WHO programme on Immunization (EPI) and the National Immunization Programme in India recommend a primary course of 3 doses of OPV at one month intervals, commencing the first dose when infant is 6 weeks old, OPV is given currently with DPT. BCG can be given with the first dose of OPV. It is very important to complete vaccination of all infants before 6 months of age. This is because most polio cases occur between the ages of 6 months and 3 years. One booster dose of OPV is recommended 12 to 18 months later.
Viral hepatitis may be defined as the infection of liver caused by half a dozen viruses viz.- hepatitis A virus (HAV), hepatitis B virus (HBV), hepatitis D virus (HDV or the delta agent), epidemic non-A hepatitis virus and by atleast two non-A and non-B viruses.
Other viruses may be implicated in hepatitis such as cytomegalo virus, Epstein-Barr virus, yellow fever virus and rubella virus. Viruses of herpes-simplex, varicella and adenoviruses can also cause severe hepatitis in immuno-compromised individuals but are rare.
HAV causes a relatively benign disease and does not cause a major public health problem. However, HBV is responsible for severe liver damage and is associated with chronic liver diseases and hepatocellular carcinoma. It has been estimated that about 4 million people suffer every year from one or the other form of acute viral hepatitis.
It was formerly known as “infectious” hepatitis or epidemic jaundice. It is endemic in most of the developing countries. Epidemics of hepatitis A often evolve slowly; involve wide geographic areas and last many months but faecal contamination of drinking water may cause the epidemic to evolve explosively.
a. Agent Factors:
The causative agent is an enterovirus (type 72) of the Picornqviridae family. It multiplies only in hepatocytes. Virus is fairly resistant to heat and chemicals. Man is the only reservoir of infection.
b. Host Factors:
HAV is more frequent among children than in adults. Both sexes are equally susceptible.
c. Environmental Factors:
In India, the disease tends to be associated with heavy rainfall. Poor sanitation and overcrowding favour the spread of infection, giving rise to water borne and food borne epidemics.
Faecal-oral route is the major route of transmission. It may occur by direct contact or indirectly by way of contaminated water, food or milk.
Hepatitis A may be controlled through control of reservoir, control of transmission, control of susceptible population, and vaccination. The best method to curtail infection is by promoting simple measures of personal and community hygiene. Community water supplies should be purified by flocculation, filtration and adequate chlorination. Vaccine is under the process of development.
Hepatitis B is the major health problem in India. It is estimated that there will be 400 million HBV patients in the world if HBV vaccine is not used widely.
i. Agent Factors:
Hepatitis B virus was discovered by Blumberg in 1963. HBV is complex, 42 run, double shelled DNA virus, originally known as the “Dane particle”. It replicates in the liver cells. Contaminated blood is the main source of infection. Man is the only reservoir of infection.
ii. Host Factors:
Highest infection is found in 20-40 year age group. Risk groups comprise surgeons; health care and laboratory personnel, recipients of blood transfusion, homosexuals, prostitutes and percutaneous drug abusers. Serological screening and vaccination of high risk groups is highly recommended.
Different measures are available to contain the disease. Hepatitis B vaccine, RDNA– yeast derived vaccine, hepatitis B immunoglobin (HB16), simultaneous administration of HBIG and the hepatitis vaccine are presently being practiced.
How to Control Lymphatic Filariasis?
The disease “lymphatic filariasis” covers infection with three closely related microfilariae nematode worms – Wuchereria bancrofti, Brugia malayi. All three infections are transmitted to man by the bite of infective mosquitoes.
The disease manifestations range from none to both acute and chronic manifestations, such as lymphangitis, lymphadenitis, elephantiasis of genital organs legs and arms or as a hypersensitivity state such as tropical pulmonary eosinophilia or a typical filarial arthritis. Though not fatal, the disease is responsible for considerable suffering deformity and disability.
Filariasis is a global problem. A WHO expert committee has estimated that 750 million are actually infected. Lymphatic filariasis is a major public health problem in India. 396 million people were found to be infected in 1993. Heavily infected areas are found in Uttar Pradesh, Bihar, Andhra Pradesh, Orissa, Tamil Nadu, Kerala and Gujarat.
i. Agent Factors:
These are at least 8 species of filarial parasites that are specific to man.
The first three are responsible for lymphatic filarias is and the rest for non- lymphatic filariasis. Man is the definitive host and mosquito the intermediate host. The adult worms are usually found in the lymphatic system of man. The males are about 40 mm long and the females 50 to 100 mm long. The females are viviparous. The adult worms may survive for 15 years or more.
ii. Host Factors:
Man is the natural host. All ages are susceptible to infection. Rate of infection is higher in man. Lymphatic filariasis is often associated with urbanization, industrialization, migration of people, illiteracy, poverty and poor sanitation.
iii. Environmental Factors:
Climate is an important factor in the epidemiology of filariasis. It influences breeding of mosquitoes. Filariasis is also associated with bad drainage. Inadequate sewage disposal and lack of town planning have aggravated the problem of filariasis in India.
Filariasis is transmitted by the bite of infected vector mosquitoes. The parasite is deposited near the site of puncture. It finally reaches the lymphatic system. The dynamics of transmission depend upon man-mosquito contact.
The current strategy of filariasis control is based on:
b. Vector control
Diethycarbamazine (DEC) is the only drug available at present against lymphatic filariasis. Use of DEC medicated salt is a special form of mass treatment using very low doses of the drug over a long period of time.
Vector control may also be beneficial when used in conjunction with mass treatment with DEC. The most important element in vector control is the reduction of the target mosquito population. The mosquito population can be controlled by antilarval measures. Antilarval activities comprise chemical control, removal of Pistia plant and minor environmental measures.
National filarial control programme (NFCP) has been in operation since 1955. According to recent estimates about 396 million people are exposed to the risk of infection; 19 million manifest the disease and 25 million have filarial parasites in their blood. Under the NFCP, the following activities are being undertaken and supervised by the Director, National Institute of Communicable Diseases, Delhi.
i) Required anti larval measures
ii) Antiparasitic measures
So far, 238 out of 300 districts situated in endemic areas have been surveyed, and 175 have been found to be endemic for filariasis. At present there are about 206 filaria control units, 27 survey units and 195 filaria control clinics functioning in the endemic areas. The population protected so far is 43.43 million out of304 million at risk.
Leishmaniasis is a collective term used for a group of protozoan diseases caused by parasites of the genus Leishmania and transmitted to man by the bite of female phelbotomine sandfly. They are responsible for various syndromes viz.- Kala azar or visceral leishmaniasis (VL), cutaneous leishmaniasis (CL), muco-cutaneous leishmaniasis (MCL), anthrophonotic cutaneous leishmaniasis (ACL), zoonotic cutaneous leishmaniasis (ZCL) and post kala azar dermal leishmaniasis (PKDL) etc. However, visceral leishmaniasis or kala azar is by far the most important diseases of India.
Kala azar occurs widely throughout the world viz.- South America, South Africa, the Mediterranean countries, India and China. It is endemic in 82 countries. 350 million people are at the risk. New agro-industrial projects, large scale migration of populations, unplanned urbanization and manmade environmental changes are responsible for its epidemics.
In India, kala azar has its home in the plains of Ganges and Brahmaputra. It is known to occur in Assam, West Bengal, and Bihar Eastern districts of Uttar Pradesh, foothills of Sikkim and to a lesser extent in Tamil Nadu and Orissa.
i. Agent Factor:
Leishmania donovani is the causative agent of kala azar, (VL). L. tropica is the causative agent of cutaneous leishmaniasis (CL). L. braziliensis is the causative agent of muco-cutaneous leishmaniasis. The life cycle is completed in two different hosts- a vertebrate and an insect. There are a variety of animal reservoirs, e.g. dogs, jackals, foxes, rodents and other mammals. Indian kala azar is considered to be a non-zoonotic infection with man as the sole reservoir.
ii. Host Factors:
Kala azar can occur in all age groups. In India the peak-age is 5-9 years. Males are affected twice as often as females. Kala azar usually strikes the poorest of the poor. People who work as farm labourers, in forestry, mining and fishing are at a great risk of bitten by sandflies.
iii. Environmental Factors:
Kala azar is mostly confined to the plains. It does not occur in altitudes over 2,000 feet. The disease is generally confined to rural areas. P. argentipes is the proven vector of kala-azar. Forest clearing, cultivation projects, large water resource schemes and colonization and resettlement programmes are responsible for the infection.
In India, kala azar is transmitted from person to person by the bite of the female phlebotomine sandfly. P. argentipes which is a highly anthrophilic species. After an infective blood meal, the sand-fly becomes infective in 6 to 9 days. Transmission of Kala azar has also been recorded by blood transfusion.
In absence of an effective vaccine, the control measures comprise the following:
1. Control of reservoir
2. Sand-fly control
Since man is the only reservoir of kala azar in India, active and passive case detection and treatment of those found to be infected may be sufficient to abolish the human reservoir and control the disease. The application of residual insecticides has proved defective in the control of sandflies. For long lasting results, insecticideal (DDT) spraying should be combined with sanitation of cattle-sheds and poultry at a far distance from human dwellings and improvement of housing and general sanitation.
The risk of infection can be reduced through health education and by the use of individual protective measures such as avoiding sleeping on floor, using fine mesh nets around the bed. Insect repellants may also be used for temporary protection.