Infectious Diseases By Idura

Disease

Terminology Endemic – Diseases that are always populations. Incidence – The number of people who are diagnosed over a certain period of time. Prevalence – The number of people who have the disease at any one time Epidemic – There is a sudden increase in the number of people with the disease Pandemic – There is an increase in the number of cases throughout a continent or across the world Mortality – Death Rate

Causative Agent DiseaseCausative Agent (pathogen) Type of organism CholeraVibrio CholeraBacterium MalariaFour species of Plasmodium Protoctist HIV/AIDSHuman immunodeficiency virus (HIV) Virus TuberculosisMycobacterium Tuberculosis and M. Bovis Bacterium Smallpox (eradicated)Variola virusVirus measlesA species of MorbillivirusVirus

Cholera – Its properties PathogenVibrio Cholera Methods of TransmissionFood-borne, water-borne Global DistributionAsia, Africa, Latin American Incubation PeriodTwo hours to five days Site of action of pathogenWall of small intestine Clinical FeaturesSevere diarrhea (‘rice water’), loss of water and salts, dehydration, weakness Method of diagnosisMicroscopical analysis of feaces Annual incidence worldwide3-5 million Annual mortality worldwide

Cholera occurs in places where people do not have access to proper sanitation To reach the site of infection (the small intestine) cholera have to pass through the stomach. – If the contents are sufficiently acidic (pH less than 4.5) the bacteria are unlike to survive If it does reach, it’ll secrete a toxin, choleragen, which disrupts the functions of the epithelium lining the intestine so that salts and water leave the blood causing severe diarrhoea. Transmission of cholera

Treating and Preventing Cholera TreatingPreventing The disease can be controlled by giving solution of salts and glucose intravenously to rehydrate the body. It is important to make sure that a patients’ fluid intake equals fluid losses in urine and faeces as to maintain the osmotic balance of the blood and tissue fluid. All in all, cholera is a fairly easy disease to treat and death from cholera can be easily avoided. Proper sanitation Sewage treatment and clean water.

Strains of cholera Until 1990s, there was only one known as 01, this originated Bangladesh. In 1961, a variety of 01, known as Al Tor originated in Indonesia. Discharge of ship sewage was said to be the reason. A new strain, known as V. cholerae 0139 originated in Chennai in October – It was more virulent. – Previous exposure to El Tor didn’t give immunity.

Malaria – Its properties PathogenPlasmodium Falciparus, P.vivax, P. ovale, P. malariae Method of TransmissionInsect vector: female Anopheles mosquito Global DistributionThroughout the tropics and sub tropics (endemic in 106 countries) Incubation PeriodFrom a week to a year Site of action of pathogenLiver, red blood cells, brain Clinical feautures Method of DiagnosisMicroscopical examination of blood; ‘dipstick ‘ test for malaria antigen in blood Annual incidence worldwide216 millions in 2010 (8Fever, anaemia, nausea, headaches, muscle pain, shivering, sweating, enlarged spleen 1% cases are in Africa) Annual mortality worldwide in 2010 (90% deaths are in Africa)

Transmission of Malaria

Preventing Malaria Reduce the number of mosquitos through biological measures : – Stocking ponds, irrigation and drainage ditches and other permanent bodies of water with fish which feed on mosquito larvae – Spraying a preparation containing the bacterium Bacillus thuringiensis, which kills mosquito larvae but is not toxic to other forms of life Avoid being bitten by mosquitos, for example: Use drugs to prevent the parasite infecting people

Treating Malaria Anti malarial drugs such as quinine and choloroquine are used to treat infected people. – Choloroquine inhibits protein synthesis and prevents the parasite from spreading within the body. – Proguanil does this and has an added advantage of inhibiting the reproduction of Plasmodium inside the biting mosquito. These are prophylatic (preventative) drugs. Taken before, during and after visiting places where malaria is an endemic. In places where strains of drug resistant of plasmodium has emerged, mefloquine is used. However, it it expensive and has many side effects. Many of these cases are amongst settled immigrants visiting relatives in places where malaria is endemic who do not realize they have lost their immunity and therefore do not take prophylatic drugs

In the 1950s, the WHO coordinated a worldwide eradication program. It was not generally successful. There were two reasons : – Plasmodium became resistant to the drugs used to control it. – Mosquitos became resistant to DDT and the other insecticides that were used at the time, such as dieldrin. Worldwide control of malaria The reason doe the worldwide concern over the spread of malaria are: An increase in drug resistant forms of Plasmodium An increase in the proportions f cases caused by P.falciparum, the form that causes severe, often fatal malaria. Difficulties in developing vaccine. An increase in the number of epidemics, because of climatic and environmental changes that favor the spread of mosquitos The migration of people from areas where malaria is endemic, for economical and political reasons.

Worldwide control of malaria Three factors may see improvements in the control of malaria: – Use of modern techniques in gene sequencing and drug design – Development of vaccines targeted against different stages of parasitic life cycle – Renewed international will to remove the burden of disease from the poorest parts of the world, allies to generous donations from wealthy individuals and foundations.

AIDS – its properties PathogenHuman immunodeficiency virus Methods of TransmissionIn semen and vaginal fluids during sexual intercourse, infected blood or blood products, contaminated hypodermic syringes, mother to fetus across placenta, at birth, mother to infant in breast milk Global DistributionWorldwide, especially in Sub Saharan Africa and South-East Asia Incubation PeriodInitial incubation a few weeks, but up to ten years of more before symptoms of AIDS may develop Site of action of pathogenT-helper lymphocytes, macrophages, brain cells Clinical FeaturesHIV infection – flu like symptom then symptomless AIDS – opportunistic infections including pneumonia, TB and cancers; weigh loss, diarrhea, fever, sweating dementia

AIDS – its properties Method of DiagnosisTesing blood, saliva or urine for the presence of antibodies produced against HIV Estimated total number of people infected with HIV worldwide in million Estimated number of new cases of HIV infection worldwide in million Estimated number of deaths from AIDS related disease worldwide up to million (UNAIDS estimate)

Transmission of HIV HIV is a virus that is spread by intimate human contact; there is no vector (unlike in malaria) and the virus is unable to survive outside the human body (unlike cholera or malaria pathogens). Transmission is only possible by direct exchange of body fluids.

Treating HIV/AIDS There is no known cure, but treatment can be provided to slowdown the onset of AIDS. However, the drugs are expensive and have many side effects.

Preventing HIV/AIDS For the present, public health measures are the only way to stop the spread of HIV. People can be educated about the spread of the infection and encouraged to change their behaviour so as to protect themselves and others.

Tuberculosis

Transmission of TB TB is spread when infected people with the active form of the illness cough or sneeze and the bacteria are carried in the air in tiny droplets of liquid. Transmission occurs when people who are uninfected inhale the droplets. The increase in transmission of TB is due to : – some strains of TB bacteria which are resistant to drugs – the HIV/AIDS pandemic – poor housing in inner cities and homelessness – the breakdown of TB control programmes; partial treatment for TB increases the chance of drug resistance in Mycobacterium.

Treating TB The treatment involves using several drugs to ensure that all the bacteria are killed. The treatment is a long one (six to nine months, or longer), because it takes a long time to kill the bacteria, which are slow growing and are not very sensitive to the drugs used. People who do not complete their treatment may be harbouring drug-resistant bacteria and may spread these to others if the bacteria become active.

Antibiotocs Antibiotics are drugs that are used to treat or cure bacterial and fungal infections. Effective antibiotics show selective toxicity, killing or disabling the pathogen but having no effect on host cells. Antibiotics are derived from living organisms, although they are often made more effective by various chemical processes.

How antibiotics work? Antibiotics interfere with some aspect of growth or metabolism of the target organism such as: – Synthesis of bacterial wall – Protein synthesis – Cell surface membrane function – Enzyme action

Choosing Effective Antibiotics Bacteria are collected from faeces, food or water, and grown on an agar medium. Various antibiotics are absorbed onto discs of filter paper and placed on the agar plate. The plate is incubated, and the diameters of the inhibition zones where no bacteria are growing are measured.