A disease is a bodily disorder or a disordered state of an organ or organism. It can be defined as the malfunctioning of the body organs due to any reason. Four major diseases are described in this paper-1) African sleeping sickness, 2) Epidemic Typhus, 3) West Nile Disease, 4) Malaria
1)African Sleeping Sickness:
African Sleeping Sickness, also known as African trypanosomiasis is a systemic, parasitic disease in people and animal caused by protozoa of genus Trypanosoma brucei that is transmitted by the bite of the tsetse fly, a gray-brown insect about the size of a honeybee. These parasites are morphologically similar but cause dramatically different diseases. African Sleeping Sickness is once again threatening many countries south of the Sahara Desert. Sleeping sickness has been a major problem in Africa in the past century. The disease was almost destroyed in the Nineteen-Sixties, but has since returned. It is estimated that 300,000 – 500,000 people are infected, and about 40,000 die every year. Three major epidemics have occurred in the past hundred years, in 1896 – 1906, 1920, and 1970. African trypanosomiasis is confined to tropical Africa from north of South Africa to south of Algeria, Libya, and Egypt. Tsetse flies inhabit rural areas only, living in the woodland and thickets of the savannah and the dense vegetation along streams. Although infection of international travellers was considered rare, the number of cases in travellers, primarily to East African game parks, has increased in recent years. The World Health Organization says twenty to fifty percent of people suffer the disease in some villages in Angola, Sudan and the Democratic Republic of Congo.
East African sleeping sickness is caused by the parasite Trypanosoma brucei rhodesiense, whereas West African sleeping sickness, also known as Gambian sleeping sickness, is caused by Trypanosoma brucei gambiense. Sleeping sickness newly infects about 20,000 to 25,000 people each year and causes about 55,000 deaths each year. Each day, about 100 people die of the disease.
It is contracted through seven species of tsetse flies in the genus Glossinaact as vectors of the disease to humans. The cycle begins when a fly bites an infected mammal and ingests the parasites. The protozoans multiply and develop over a series of weeks within the gut and salivary glands of the fly. When the fly bites another human or other animal host, the mature forms of the parasite enter the host, settling in the blood and spinal fluid. Humans can also contract West African sleeping sickness spread through maternal transfer, blood transfusion, or by organ transplant. Once a fly is infected, it remains able to transmit trypanosomiasis. The signs and symptoms of the infection are initially non-specific (high fever, rash, edema, or swollen glands) but the disease progresses to encephalitis and meningitis. Symptoms begin with fever, headaches, and joint pains. If untreated, the disease slowly overcomes the defences of the infected person, and symptoms spread to anaemia, Endocrinology, and Cardiology and Kidney Diseases and disorders. Symptoms generally appear within 1 to 3 weeks of infection. People who have had tsetse fly bites or become ill with high fever or other manifestations of African trypanosomiasis are advised to seek early medical attention. The infection can usually be cured by an appropriate course of anti-trypanosomal therapy. Pentamidine isethionate and suramin are the drugs of choice to treat the hemolymphatic stage of West and East African trypanosomiasis, respectively. Melarsoprol is the drug of choice for late disease with central nervous system involvement.
Control programs were implemented around 1920 and gradually the disease was reduced or eradicated within much of its range by 1960.Two alternative strategies have been used in the attempts to reduce the African trypanosomiases. One tactic is primarily medical or veterinary and targets the disease directly using monitoring, prophylaxis, treatment, and surveillance to reduce the number of organisms which carry the disease. The second strategy is generally entomological and intends to disrupt the cycle of transmission by reducing the number of flies. Since the risk of infection increases with the number of times a person is bitten by the tsetse fly, the best means of protection against the disease involves personal measures. Sleeping sickness has a profound impact on the health of a large portion of sub-Saharan Africa. Furthermore, the economic impact of sleeping sickness is significant owing to the dramatic reduction in the labour force and resulting decrease in economic productivity. This in turn has countless added direct and indirect impacts on the quality of life of people in affected countries. The economic impact is further increased because sleeping sickness can reduce cattle production 20-40% in areas where the disease is epidemic. It is estimated that cattle-production losses alone amount to $2.7 billion each year
2) Epidemic Typhus:
Epidemic typhus is an infectious disease and results from infection by Rickettsia prowazekii, a Gram negative, obligate intracellular bacterium. At least two strains can be distinguished by genetic analysis. One strain is found only in humans; the other also occurs in flying Squirrels in the United States. It is known to people by various synonyms that are Murine typhus; Epidemic typhus; Endemic typhus; Brill-Zinsser disease and Jail fever. Hospital Fever or Famine fever is carried by the human body louse Pediculus humanus. Feeding on a human who carries the bacillus infects the louse. R. prowazekii grows in the louse’s gut and is excreted in the feces. Typhus group rickettsioses are distributed worldwide. Foci of disease currently exist in many countries in Asia, central and east Africa, and the mountainous regions of Mexico, Central and South America. War and famine can result in explosive outbreaks of disease Rickettsial typhus has two forms: endemic typhus and epidemic typhus. In the United States, R. prowazekii is endemic in flying squirrels. This form is zoonotic; sporadic human cases have been seen in Georgia, Virginia, West Virginia, North Carolina, Tennessee, Indiana, Illinois, Ohio, Pennsylvania, Maryland, Massachusetts, New Jersey, New York and California.
Typhus group rickettsioses, especially epidemic typhus, are associated with wars and human disasters. According to Waclaw Szybalski, the first description of typhus was given in 1083 in a convent near Salerno, Italy. Before World War II, epidemic typhus was a devastating disease for humans. Epidemics occurred throughout Europe from the 17th to the 19th centuries. During World Wars II, and I typhus spreads through North Africa, the Pacific Islands, and Europe, especially in German concentration camps. Political instability in Eastern European and African countries has recently caused conflicts in regions where the risk for typhus outbreaks is very high. In Yugoslavia and Rwanda, older persons who contracted epidemic typhus as youths can develop recrudescent illness and become the source of resurgent epidemics if louse infestation becomes prevalent. Recently, an outbreak of typhus was suspected in a Burundi jail. Epidemic typhus and Brill disease are uncommon in the United States. It is frequently seen in the summer and fall and typically lasts two to three weeks. Risk factors for murine typhus include exposure to rat fleas or rat feces, or exposure to other animals (such as cats, opossums, raccoons, skunks, and rats). Epidemic typhus occurs in poor hygienic conditions.
The disease is transmitted to an uninfected human who scratches the bite and rubs the feces into the wound. Incubation period is one to two weeks. R. prowazekii can remain viable and virulent in the dried feces for many days. The disease will kill the louse and it will remain viable for many weeks in the dead louse. Endemic typhus is, usually transmitted to humans by the rat flea, Xenopsylla cheopis. In the United States, R. prowazekii has also been found in a sylvatic cycle involving flying squirrels and their ectoparasites
The onset of epidemic typhus is often sudden. The symptoms set in quickly, and are among the most severe of the typhus family. They include severe headache, a sustained high fever, cough, rash, severe muscle pain, chills, falling blood pressure, stupor, sensitivity to light, and delirium, prostration and myalgia. A rash begins on the chest about five days after the fever appears, and spreads to the trunk and extremities but does not reach the palms and soles. The infection is treated with antibiotics. Intravenous fluids and oxygen may be needed to stabilize the patient. The mortality rate is 10% to 60%, but is vastly lower if antibiotics are used early. Typhus is usually exanthematic, and a careful clinical examination will find a rash in more than half of the cases. The typhus exanthema is frequently purpuric and is observed even on dark skin in 33% of cases. As the disease progresses, the rash usually becomes dark and maculopapular or, in severe cases, petechial and hemorrhagic. Splenomegaly, hypotension, nausea, vomiting and confusion may also be seen. The fever lasts approximately 2 weeks. In seriously ill patients, vascular collapse, renal insufficiency, ecchymosis with gangrene, the other typical symptoms are neurological signs including seizures, coma, and mental confusion.
The first major step in the development of the vaccine was Charles Nicolle’s 1909 discovery that lice were the vectors for epidemic typhus. This made it possible to isolate the bacteria causing the disease and develop a vaccine. Delousing is critical to typhus prevention. The treatment for typhus is simple and inexpensive: a single dose of 200 mg of doxycycline provides cure. A safer, mass-production-ready method was determined by Herald R. Cox in 1938, involving egg yolk, and this was tested and put into heavy use by 1943.
The major risk for exanthematic typhus is in central eastern Africa including Burundi, Zaire, and Rwanda and the importance of sending lice to reference laboratories to identify the pathogens when a typhus outbreak is observed. Molecular identification by PCR and sequencing offers a rapid, sensitive, and specific identification method for Rickettsia, even when epidemiological investigations are undertaken.
3)West Nile Disease:
West Nile disease is spread through a virus of the family Flaviviridae, found in both tropical and temperate regions. It mainly infects birds, but is known to infect humans, horses, cats, bats, chipmunks, skunks, squirrels, and domestic rabbits. The main route of human infection is through the bite of a typical infected mosquito. West Nile Virus originated in remote areas such as Africa, Eastern Europe, West Asia, and the Middle East. Studies conducted by the Centres for Disease Control and Prevention have documented nine hundred fifty-four human cases of West Nile Virus in the United States in 2002. Illinois, Louisiana, Michigan and Mississippi were the areas most affected. Recent outbreaks of West Nile virus encephalitis in humans have occurred in Algeria (1994), Romania (1996 to 1997), the Czech Republic (1997), Congo (1998), Russia (1999), the United States (1999 to 2003), Canada (1999–2003), and Israel (2000). West Nile virus spread among horses in Mexico. The first human West Nile disease in 2003 occurred in June and one West Nile-infected blood transfusion was also identified that month. In the 2003 outbreak, 9,862 cases and 264 deaths were reported by the CDC.
Mosquitoes contract West Nile Virus when they feed on infected birds. Female mosquitoes, mainly of the species Culex pipiens, Culex restuan, and Culex quinquefasciatus, bite infected birds, carry the virus in their salivary glands, and infect other birds when they bite again The infected blood circulates within a mosquito’s salivary glands for a few days. When an infected mosquito bites a human or animal it may take three to fourteen days for West Nile Virus symptoms to be evidence for. Most people infected with the virus have no symptoms or they have flu-like symptoms or it can result in permanent neurological affects or even death. West Nile virus can infect both humans and certain animals including horses, many types of birds and certain other mammals. Over one hundred ten species of birds have been known to infection. There is no evidence to suggest that it can be spread from person to person or from animal to person. It has only been documented spreading by infected mosquitoes. It can be diagnosed by employing an ELISA test detecting IgM antibodies against the virus.
There is no vaccine for humans. A vaccine for horses based on killed viruses exists. West Nile virus can be sampled from the environment by the pooling of trapped mosquitoes, testing avian blood samples drawn from wild birds and sentinel chickens, as well as testing dead birds found by various animal control agencies and the public. West Nile control is achieved through mosquito control, by elimination of mosquito breeding sites, and encouraging personal use of mosquito repellents. The public is also encouraged to spend less time outdoors, wear long covering clothing and ensure that mosquitoes cannot enter buildings. To combat the spread of West Nile virus, which is transmitted by mosquitoes, Pennsylvania has developed a comprehensive network The Public Health Agency of Canada coordinates national surveillance and response to West Nile virus. The Agency works closely with Health Canada on the safety of the blood supply and on providing information and health advice to First Nations groups and federal employees.
Malaria is a common infection in hot, tropical areas but can also occur in temperate climates. Malaria, derived from mala aria and formerly called ague or marsh fever, is an infectious disease, which causes about 350-500 million infections with humans and approximately 1.3 – 3 million deaths annually. India is one of the malaria endemic regions of the world. Worldwide, 300-500 million people are infected with malaria each year. Most cases occur in sub-Saharan Africa, with approximately 2 million people dying there each year. Malaria is rare in the United States. Malaria is more common in rural areas than in cities; this is in contrast to dengue fever where urban areas present the greater risk. Doctor Charles Louis Alphonse Laveran showed in 1898 that certain mosquito species transmit malaria to birds. Juan Carlos Finley, a Cuban doctor, first suggested that mosquitoes could transmit disease to humans.
Malaria is caused by the protozoan parasites of the genus Plasmodium (of the phylum Apicomplexa), and the transmission vector for human malarial parasite is the female Anopheles mosquito. Only females feed on blood, thus males do not transmit the disease. The Anopheles species prefer to feed at night. Young mosquitoes first ingest the malaria parasite by feeding on a human carrier. Infected female Anopheles mosquitoes carry Plasmodium sporozoites in their salivary glands. When an infected mosquito pierces a person’s skin to take a blood meal, the sporozoites in the mosquito’s saliva enter the bloodstream and migrate to the liver. Within the red blood cells they multiply further, again asexually, periodically breaking out of the exploited red blood cells to invade fresh red blood cells and start the amplification cycle anew. The classical description of waves of fever coming every two (Plasmodium falciparum) or three days (Plasmodium vivax) arises from simultaneous waves of merozoites breaking out of red blood cells during the same day. The diagnosis of malaria is microscopic examination of blood films, because each of the four major parasite species has distinguishing characteristics. Once malaria parasites enter the bloodstream, they travel to the liver and multiply. Every few days, thousands of parasites are released from the liver into the blood, where they destroy red blood cells. Some parasites also remain in the liver and continue to multiply, releasing more parasites into the blood every few days. The incubation period for malaria is the time between the mosquito bite and the release of parasites from the liver. This varies, depending on which malaria parasite is causing the disease. In general, it can range from 10 days to a month.
Symptoms of malaria include fever, shivering, arthralgia (joint pain), vomiting, anaemia caused by haemolysis, haemoglobinuria, and convulsions. There may be the feeling of tingling in the skin, particularly with malaria caused by P. falciparum. Consequences of infection with malaria include coma and death if untreated. Young children and pregnant women are especially vulnerable. Splenomegaly (enlarged spleen), severe headache, cerebral ischemia and hemoglobinuria with renal failure may occur. There are several families of drugs used to treat malaria. . Chloroquine was the antimalarial drug used to treat malaria. However, resistance of Plasmodium falciparum to chloroquine has spread recently from Asia to Africa, making the drug ineffective against the most dangerous Plasmodium strain in many affected regions of the world. Some currently available anti-malarial drugs are Artesunate-amodiaquine, Atovaquone-proguanil, Quinine, Chloroquine, Doxycycline, Mefloquine, Primaquine . A team of French and South African researchers had identified a new drug they were calling “G25”. It cured malaria in test primates by blocking the ability of the parasite to copy itself within the red blood cells of its victims. The disease remains a threat to people living in endemic areas who have no proper and prompt access to effective drugs. Access to pharmacies and health facilities, as well as drug costs, are major obstacles. Médecins Sans Frontières estimates that the cost to treat a malaria-infected person in an endemic country is between US$0.25 and $2.40. There is a problem of availability of effective malaria treatments in the United States. Methods used to prevent the spread of disease, or to protect individuals in areas where malaria is endemic, include prophylactic drugs, mosquito eradication, and the prevention of mosquito bites. There is currently no vaccine that will prevent malaria, but this is an active field of research. Malaria costs Africa US$12 billion a year in lost productivity. Economic adviser Jeffrey Sachs estimates that malaria can be controlled for $3 billion a year. In 2004, the US gave $500 Million in anti-malaria aid.
While reviewing above four diseases, it can be stated that all diseases deadly affect human life. The epidemic zone for malaria, sleeping sickness, typhus fever are global tropic and sub tropic areas; east, west and central southern Africa; worldwide respectively. Scientists expect the number of West Nile infections to reach record numbers next summer, in which case the comparisons to other mosquito-borne diseases will include the malaria epidemic of 1914, during which 60,000 people were infected. Hutchinson said that West Nile virus would be around much longer than malaria. In the transmission cycle, mosquitoes, birds and parasites all develop immunities eventually over time. A number of West Nile virus cases next year may not be so bad because all the diseased birds may die off. Unlike the geographic specificity of malaria, West Nile outbreaks occur wherever mosquitoes live. In case of malaria, it occurs in over 100 countries and more than 40% of the people in the world are at risk. Large areas of Central and South America, Hispania (Haiti and the Dominican Republic), Africa, the Middle East, the Indian subcontinent, Southeast Asia, and Oceania are considered malaria-risk areas. Records indicates sleeping sickness is approaching epidemic levels in Angola, the Democratic Republic of Congo, Uganda, Sudan, Cameroon, Cote d’Ivoire, Central African Republic, Guinea, Mozambique, Tanzania, and Chad. This disease organism is concentrated close to settlements where humans contact it during daily activities. West African sleeping sickness only requires a small vector population to maintain high levels of the trypanosome in a local population, make this form of sleeping sickness particularly difficult to eradicate locally.
Epidemic typhus is spread through lice and ticks, only likely to affect volunteer workers who come into close contact with locals. Data shows that at least 36 species of mosquito are known to be carriers of West Nile Virus. The World Health Organization estimates that each year 300-500 million cases of malaria occur worldwide and more than two million people die of malaria. Sleeping sickness occurs in sub-Saharan Africa. Wild game mammals are the primary reservoir for the disease. Humans contract it when they travel outside the villages. West African sleeping sickness has a much wider range in Western and Central Africa; it is found in forests, near dense shrubs, and by rivers and watering holes. Humans and other animals are the primary reservoir.
West Nile fever is usually a case of mild disease characterized by flu-like symptoms. Many people who are infected with the West Nile virus will not have any type of illness. It is estimated that 20% of the people who become infected will develop West Nile fever. The severity of the illness of typhus fever depends on the variety of typhus. Social conditions are critical factors influencing the re-emergence of disease. Louse infestation occurs when cold weather, poor hygiene, and poverty are prevalent. Neurological involvement was prominent in Typhus fever cases. Coma, seizures, mental confusion, and hallucination are major symptoms that differ from rest diseases mentioned. When observing sleeping sickness, early signs include high body temperature, muscle pain and a tired feeling. The signs become worse later when the parasite invades the brain. Treating sleeping sickness is costly. Malaria may cause anaemia and jaundice. If not promptly treated, may cause kidney failure, seizures, mental confusion, coma, and death. Unlike Nile virus and typhus fever, Malaria can be cured with prescription drugs. Adventure travellers are usually more exposed to malaria than ordinary travellers.
Typhus fever can be fatal but responds well to antibiotic therapy using tetracyclines if given early enough. There are no vaccines available for any form of typhus. There is no specific treatment for West Nile virus infection. In more severe cases, intensive supportive therapy is indicated. The drug treatment of malaria depends on the type and severity of the attack. Typically, Quinine Sulphate tablets are used. Nile Viruses can show resistance, but not in the way that a protozoan, like malaria, can quickly become resistant to antibiotics. Medical experts say early treatment can cure African sleeping sickness. Treating sleeping sickness is costly. No vaccine is available to prevent this disease.
Instances of sleeping sickness are being reduced by the use of the Sterile Atomic Fly. Regular active surveillance, involving case detection and treatment, in addition to tsetse fly control, is the backbone of the strategy for control of sleeping sickness. Since the risk of infection increases with the number of times a person is bitten by the tsetse fly, the best means of protection against the disease involves personal measures. To arrest Nile virus disease, repellents containing DEET and mosquito netting are still the best forms of protection from mosquito bites. Malaria is most common and spread worldwide, great efforts are being made to eradicate this disease by eliminating mosquitoes. It has been successful in some areas. Malaria was once common in the United States and southern Europe, but the draining of wetland breeding grounds and better sanitation, in conjunction with the monitoring and treatment of infected humans, eliminated it from affluent regions. However, these efforts have so far failed to eradicate malaria in many parts of the developing world – the problem is most prevalent in Africa. The United States itself may face the spread of malaria in the future as climate change (warming) leads to an expansion of the areas in which mosquitoes are active. In the long run, it seems that Malaria prevention is likely to be more cost-effective than disease treatment; however, disease prevention programs typically require funding for capital costs.
It is concluded that Malaria, Typhus fever and sleeping sickness spread by insect bite, and very dangerous when these are at chronic stage whereas Nile virus is caused by virus. It is the most dreaded one when a person being infected with this virus can have West Nile encephalitis. It is emphasized that Malaria and sleeping sickness represent major health problems and in which severe involvement of the nervous system is frequently the direct cause of death. The historical contribution to the pathogenesis and therapy of malaria is by a renowned pioneer in neuroscience. Strategies in African trypanosomes include sites favourable for hiding or replication of the parasites in the host, antigenic variation, and interactions with the cytokine network of the host. Researchers have made a crucial breakthrough in the journey towards finding a treatment for African sleeping sickness. Researchers have discovered a weakness in the parasite that causes the disease – it cannot survive in the human bloodstream without the use of its flagellum, a protein ‘tail’ that allows it to swim. It offers up a valuable lead in the search for new drugs to control the killer disease.
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