Hereditary Diseases
Hereditary diseases cannot be cured because of how they are transmitted. Until it becomes possible to alter the genetic makeup of an individual only by the symptoms of genetic disorders can be controlled. In all cases of hereditary diseases, genetic counseling is advised.
Haemophilia, or ‘bleeder’s disease’, is a disease where the blood fails to clot or clots at a very slow rate resulting in excessive bleeding from small cuts and wounds. Persons suffering with this disease could be informed on what to expect and what activities to avoid. Various commercial preparations are now available which encourage blood clot formation in cases of severe bleeding. These clotting factors are taken from the body of healthy individuals.
Physiological Diseases
Most physiological diseases cannot be completely cured but their symptoms may be controlled through diet, exercise and/or drugs, as seen with diabetes and hypertension. Improvements in nutrition and lifestyle changes are also important in preventing physiological disorders. In this connection, public awareness and education are very important in reducing the incidence of these diseases (both of which are very common in the Caribbean).
Diabetes is the condition where the body is unable to regulate the concentration in the blood because the pancreas fails to secrete enough of the hormone insulin. There is a high blood glucose level and excretion of glucose in the urine. There are two types of diabetes:
Type 1, insulin dependent diabetes, is a severe form of the disease which usually starts in early life. It is caused by the destruction of the insulin producing cells of the pancreas, the islets of Langerhans. Treatment is the administration of insulin by injection.
Type 2, non-insulin dependent diabetes, usually starts later in life and has no cause. In many cases it is associated with being overweight or consuming large quantities of sugary foods for many years. Blood glucose levels can be controlled by weight loss and diet of drugs which stimulate the pancreas to increase its production of insulin.
Hypertension is the condition where the blood pressure remains above normal leve;s usually due to narrowing or hardening of the arteries. In some cases fatty material is deposited in the arteries reducing the space through which blood must be forced by the heart. A high salt and fat intake, overweight, lack of regular exercise, stress and smoking all contribute to hypertension.
The roles of diet and exercise
Diabetes and hypertension are both treated by sticking to low calorie diets. In the case of diabetes particular attention should be paid to carbohydrate intake especially that of sugar. For hypertension, the intake of fat should be drastically reduced and the amount of salt kept to a minimum. Regular exercise and changes in life style would also help to control hypertension and diabetes. Exercise helps to burn up sugar, reducing its level in the blood and preventing obesity. It also reduces stress. Drugs can also be taken to reduce the blood pressure.
Vectors
A vector is an organism that transmits a disease causing organism from one person to another. It carries pathogen either inside or outside the body. Mosquitoes, for example, carry the pathogen for malaria and dengue fever inside their bodies. Houseflies may carry the pathogens for cholera, typhoid fever and gastro-enteritis on their bodies.
Vectors such as the housefly provide a mechanical means of transmission for pathogens. When the vector crawls or walks on contaminated material, mainly faeces, pathogens become attached to body hairs or sticky pads on the feet. These pathogens are then deposited on foods as the insect flies over or walks on the food. Alternately, the organisms may pass through the vector’s digestive tract and may be deposited on the food in its faeces or saliva.
When, however, a pathogen is carried inside the vector, the vector acts as a second host in which the pathogen has to complete part of its life cycle. Transmission may be by saliva during biting by regurgitation or deposition on the skin, in which case, the pathogen penetrates into the body when the host rubs or scratches the skin.
Life History of the Mosquito
The mosquito is a vector for a number of diseases including malaria, dengue fever, yellow fever and elephantiasis. Different species of mosquito carry different diseases. In the absence of mosquitoes, the pathogens cannot complete their life cycle and would be therefore be unable to cause diseases. Hence eliminating certain species of mosquitoes can eradicate the disease they spread.
Although diseases transmitted by mosquitoes may be cured by using drugs, or prevented by isolating infected persons and protecting others from being bitten, the best control measure is to destroy the mosquitoes in all their different developmental stages and to destroy their breeding places. A knowledge of their life history and habits is therefore essential.
Adult mosquitoes usually lay their eggs on the surface of stagnant water. The Aedes aegypti, which carries yellow fever and dengue, prefers clean water. Within a few days the hatch into active larvae, sometimes called wrigglers, which feed on microscopic organisms in the water. The larvae breathe using air tubes which obtain atmospheric oxygen and gills which extract oxygen dissolved in the water. They grow and feed for about a week or two and then change inot pupae. Pupae can hang from the surface of the water and breathe in air. Inside the pupal case larval tissue are reorganized to form adult organs. After a few days a young adult emerges.
The mature female mosquito requires a meal of blood for her eggs to mature. When she bites an individual she secretes saliva which prevents blood from clotting. If she bites an infected person she takes in the pathogens with the blood. The pathogen goes through a stage of its life and cycle and enters the salivary glands of the mosquito. When an infected mosquito bites a healthy person, saliva containing the pathogens is injected into the person’s blood.
The adult, larvae and pupae can be killed using chemicals. Breeding places should be drained frequently (e.g. drains and pools) or removed (e.g. empty pins and bottles). Where draining is not possible (e.g. lakes) the surface can be sprayed with oil. This reduces the surface tension of water and larvae and pupae would be unable to breathe. This method is no longer used on a large scale because it causes death of many other aquatic organisms. Biological control has become increasingly popular. This involves introducing natural predators, of the larvae and pupae, e.g. fish, into the water.
Life History of the Housefly
Houseflies are household pests. They spread diseases by collecting pathogens on their hairy bodies, on sticky pads on their feet or taking them in along with food into their digestive systems. Pathogens are picked up from faeces, sewage and rotting material and deposited on food, drinks ar open wounds. They do not discriminate in their food source and may fly from a rotting animal to garbage and then to prepared foods in the kitchen, all in a few minutes. They defecate on the food while they feed and may also regurgitate semi-digested food.
The adult female housefly lays eggs in moist rotting animal and plant material including human faeces. If conditions are favourable, within a few hours to about three days, larvae or maggots emerge. The larval stage lasts for about one week to two weeks during which the larvae feed, grow and moult. The larvae then change into pupae. Pupae do not feed. Inside, the larval tissues are broken down and adult structures develop. A few days later a young adult emerges. Within two weeks, an adult becomes sexually mature and can begin to lay eggs.
Knowledge of this life cycle is important in getting rid of houseflies and preventing them from spreading disease. Potential breeding grounds should be destroyed. Adults and maggots can be killed with chemicals. Foods for human consumption should be properly stored and kept covered.
AIDS AND OTHER SEXUALLY TRANSMITTED DISEASES
AIDS
Causative Agent: Acquired Immunodeficiency Syndrome (AIDS) is the progressive destruction of the immune system by the Human Immunodeficiency Virus (HIV). When a person is infected with HIV, the virus binds to the surface of specific white blood cells (called T4 cells or helper cells) and inactivates or destroy these cells which are an important part of the immune system. This weakens the immune system. The infected person becomes susceptible to pathogens which are normally destroyed by these cells and vulnerable to a wide range of diseases. Death results from any of these diseases.
Transmission: AIDS was first diagnosed in 1981 in a small population of homosexual men but now occurs in heterosexual males and females with multiple sexual partners, haemophiliacs, intravenous drug users infants and small children.
HIV may be transmitted by any activity which allows body fluids of an infected person to enter the bloodstream of another person. This may take place:
During sexual intercourse;
By sharing contaminated needles to inject drugs;
By blood transfusion with blood from infected person;
If there is close contact between cuts and open wounds of infected and non infected persons
From an infected person to her developing baby through the placenta or to her breast feeding infant through breast milk
It is not spread by casual contact or through sneezing and coughing.
Signs, symptoms and nature of the disease: After exposure to the virus, there is a period between six weeks to years before the virus or an antibody against the virus is detected in the blood. Infection with HIV does not necessarily result in AIDS.
The infected person may not develop symptoms for many years. The most common symptom is swollen lymph nodes. Fatigue, fever, chronic diarrhoea and a rash may appear later. Some infected persons never experience any symptoms and are termed carriers. They make antibodies against the virus, which can be detected by a blood test.
As the immune system deteriorates, the disease progresses to what is known as full blown AIDS and a wide range of illnesses appear. These include a rare type of pneumonia, a rare and disfiguring type of skin cancer, known as Kaposi’s sarcoma, other forms of cancer and tuberculosis.
Control
To date there is no known cure for AIDS. In 1994, WHO estimated 18 million people worldwide were infected with HIV. New infections were occurring at a rate of 10,000 new infections per day. AIDS can be controlled if the spread of HIV is reduced. This could be achieved in several ways:
Modifying sexual behavior; abstinence, one safe partner and the use of barrier methods such as condoms during intercourse
Using clean needles and syringes;
Testing all donated blood for the presence of antibodies to HIV;
Educating the public about the disease through the media, emphasizing its method of transmission and the risks involved ;
Testing pregnant women for the antibodies and administering early treatment to reduce the risk of babies being infected;
Testing all newborn babies for the antibodies against HIV and then identifying, informing and treating infected mothers.
Insisting on safety precautions e.g. use of gloves, goggles, gowns, for health care practitioners.
For those persons already infected with the virus and suffering with AIDS, certain drugs are used to prevent and treat many of the diseases that typically develop. These drugs are costly and not readily available in third world countries. A recently developed drug seems to be able to prevent the virus from multiplying.
Other Sexually Transmitted Diseases
AIDS can be sexually transmitted, however, sexual intercourse is not the only method of transmission. Gonorrhea, syphilis and Herpes genitalis are three diseases transmitted through sexual intercourse.
GONORRHOEA
Causative Agent: Gonorrhoea, commonly known as the ‘clap’, is worldwide in distribution and very common. It is caused by a bacterium. Mortality rates from gonorrhea are negligible but it is responsible for a very high percentage of sterility in males as well as females.
Transmission: The bacterium is transmitted during sexual intercourse with an infected person.
Signs and Symptoms: In males, the first symptoms are a burning sensation during urination and a mild discharge. In females, in most instances, symptoms are so mild they tend to go unnoticed. Untreated, infection may spread and cause blocking of tubes rendering females sterile.
Treatment: The use of the antibiotic penicillin is very effective in curing the disease.
SYPHILLIS
Causative Agent: syphilis is caused by a bacterium. It is rare in developed countries but very common in underdeveloped countries.
Transmission: syphilis may be transmitted from an infected mother across the placenta to her unborn child. The main means of transmission is through sexual contact.
Signs and symptoms: During the early stages of infection, a small, hard, painless swelling occurs on the site of infection. This may go unnoticed and heals without treatment. The infected person then develops a rash on the face, trunk and limbs which may last for several weeks. This may disappear spontaneously. If untreated, about ten years later, some persons may show severe symptoms some of which may be fatal. These may include intense back pains, lack of muscular coordination, wasting of muscles, blindness and heart attacks.
Treatment: Infected persons can be successfully treated by antibiotics.
HERPES GENITALIS
Causative Agent: Herpes, like AIDS, is caused by a virus.
Signs and symptoms: A small, red, painful sore appears on the genital organ of both sexes. Swollen glands and fever develop. These symptoms disappear after a few weeks but may return at irregular intervals during the person’s lifetime, especially during times of stress or when the person’s resistance is low.
Treatment: There is no known cure for the herpes genitalis. Drugs exist which make the sore less painful. Sexual intercourse should be avoided to prevent transmission to uninfected persons.
Control of STDs
Sexually transmitted diseases are preventable. Their spread can be controlled by:
Restricting sex to one partner
Tracing contacts: this is especially important with gonorrhea because the woman may not develop any symptoms
Effective diagnosis and treatment; vague symptoms may cause the disease to go unnoticed
Education; knowning the facts about STDs is very important in its prevention
Use of condoms
Social implications of STDs
The treatment of diseases including STDs involves a cost. The treatment and care of persons with a lifelong illness is very costly to a family, as well as to a country. Prevention of these diseases can be very cheaply and easily achieved.
A country has to provide medical services in the form of drugs, specialized care, counselling to patient and family members. This puts a strain on limited resources especially in developing and underdeveloped countries.
Persons with STDs, especially those infected with HIV are often shunned by family members as well as society. They become afraid, lonely, depressed and confused and there are few public facilities to take them in.
STDs are more common among the age group which, at the time of infection, are contributing to the development of their family and country. When they are ill and can no longer make a meaningful contribution, their families suffer. When the final outcome is death, then there is a tragic loss of family and country. Many parents die because of AIDS leaving children which become the responsibility of their family members or the state.
STDs can spread very rapidly through a population, largely because of ignorance. Persons ignore symptoms or keep their illness a secret from partners. Those who do go for treatment may not reveal the name of their partners. Many use home remedies which cannot cure the disease although some of them mask the symptoms.
DEFENSE AGAINST DISEASE
The blood plays an important role in defending the body against disease. A scratch, cut or wound on the skin serves as a point of entry for pathogens which could result in pathogenic diseases. These organisms should be prevented from entering and once entered should be quickly destroyed.
The body responds to this in several ways:
Formation of the blood clot
Engulfing and destroying invading organisms, especially bacteria
Production of antibodies
Antibody production can also be induced artificially.
Clotting of blood
The formation of blood clot is natural defense mechanism of the body. This seals the wound, reduces the loss of blood, and prevents the entry of pathogens in the body. In addition when the blood clot hardens into a scar, it protects the delicate new tissue while the area is being repaired.
Clotting is a complex process. In the blood are a number of substances which are essential for clot formation. These include the proteins prothrombin and fibrinogen, calcium ions and vitamin K. When a blood vessel is damaged, the damaged platelets and cells release a chemical which helps to convert prothrombin and thrombin. Thrombin acts on fibrinogen converting it to insoluble fibrin. Fibrin forms a network of fibre across the wound which traps red blood cells and platelets. This forms a clot. Beneath the clot, new tissue grows and heals the wound.
Phagocytes
Once pathogens have entered the bloodstream, they can be transported all over the body. They must be quickly destroyed before they cause disease. Phagocytes are one type of white blood cell which defends against the microorganisms. They destroy bacteria circulating in the blood, or at the site of a wound, by engulfing and digesting them with an ameoeboid action. Some of the phagocytes are killed by the toxins produced by the pathogens. The dead cells collect at the wound as a white fluid known as pus which gradually becomes absorb as the wound heals.
Lymphocytes and natural immunity
Lymphocytes, another type of white blood cell, respond to foreign organisms, e.g. pathogens, in the blood, by making special protein molecules called antibodies. Any substance that stimulates the production of antibodies is called an antigen. The foreign organisms are called antigens. the antibodies act against the antigens, either destroying them or making them harmless. Antibody production is slow at first but as long as the antigens remain in the blood, antibody production increases until the disease is overcome. Some pathogens produce toxic chemicals called toxins. Lymphocytes produce antitoxins which neutralize them.
Antibodies are specific in action. Each type of antibody can combine with one type of antigen. Once the lymphocytes have been stimulated to make a particular antibody, they remember how to make them. If the same antigens enter the body, the lymphocytes immediately recognize them and rapidly produce large numbers of the right antibodies, before they can cause disease. The individual does not become ill and is said to be immune to that disease. This is known as natural immunity. Immunity is the ability to resist infection.
Artificial Immunity
There are some diseases, for which the body cannot make antibodies fast enough to prevent illness. Some of these are either fatal or likely to leave a person with physical disabilities, e.g. polio, if the person survives. A person can be artificially protected against such a disease by vaccination. This process involves the introduction of a preparation called a vaccine which may be administered orally or by injection. The process of giving the vaccine is called inoculation.
A vaccine is made from pathogens that have been killed or weakened by some treatment. In this state, these organisms are unlikely to cause disease but they are still recognized as foreign. The lymphocytes therefore produce antibodies against them, just as they would during an actual attack. The person has obtained artificial immunity. For some diseases, e.g. typhoid and cholera antibody levels reduce with time. A second or third dose of the vaccine, called boosters, is needed to maintain the antibody levels, so the person remains protected.
‘Ready -made’ antibodies can also be introduced into the blood stream. This is done when immediate protection is necessary. For example when a person is exposed to a deadly disease, such as rabies, there is no time to make antibodies. Antibodies are quickly injected to protect the individual. This immunity lasts only a short time, as the injected antibodies are themselves destroyed.