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21 January, 2019 00:00 00 AM

Infectious diseases

WHO
Infectious diseases

Infectious diseases are caused by pathogenic microorganisms, such as bacteria, viruses, parasites or fungi; the diseases can be spread, directly or indirectly, from one person to another. Zoonotic diseases are infectious diseases of animals that can cause disease when transmitted to humans.

What is TB? How does it spread? How is it treated?

Tuberculosis (TB) is caused by bacteria (Mycobacterium tuberculosis) that most often affect the lungs. Tuberculosis is curable and preventable.

TB is spread from person to person through the air. When people with lung TB cough, sneeze or spit, they propel the TB germs into the air. A person needs to inhale only a few of these germs to become infected.

About one-third of the world's population has latent TB, which means people have been infected by TB bacteria but are not (yet) ill with disease and cannot transmit the disease.

People infected with TB bacteria have a lifetime risk of falling ill with TB of 10%. However persons with compromised immune systems, such as people living with HIV, malnutrition or diabetes, or people who use tobacco, have a much higher risk of falling ill.

When a person develops active TB (disease), the symptoms (cough, fever, night sweats, weight loss etc.) may be mild for many months. This can lead to delays in seeking care, and results in transmission of the bacteria to others. People ill with TB can infect up to 10-15 other people through close contact over the course of a year. Without proper treatment up to two thirds of people ill with TB will die.

Since 2000, 53 million lives have been saved through effective diagnosis and treatment. Active, drug-sensitive TB disease is treated with a standard 6-month course of 4 antimicrobial drugs that are provided with information, supervision and support to the patient by a health worker or trained volunteer. The vast majority of TB cases can be cured when medicines are provided and taken properly.

What is multidrug-resistant tuberculosis and how do we control it?

The bacteria that cause tuberculosis (TB) can develop resistance to the antimicrobial drugs used to cure the disease. Multidrug-resistant TB (MDR-TB) is TB that does not respond to at least isoniazid and rifampicin, the 2 most powerful anti-TB drugs.

The 2 reasons why multidrug resistance continues to emerge and spread are mismanagement of TB treatment and person-to-person transmission. Most people with TB are cured by a strictly followed, 6-month drug regimen that is provided to patients with support and supervision. Inappropriate or incorrect use of antimicrobial drugs, or use of ineffective formulations of drugs (such as use of single drugs, poor quality medicines or bad storage conditions), and premature treatment interruption can cause drug resistance, which can then be transmitted, especially in crowded settings such as prisons and hospitals.

In some countries, it is becoming increasingly difficult to treat MDR-TB. Treatment options are limited and expensive, recommended medicines are not always available, and patients experience many adverse effects from the drugs. In some cases even more severe drug-resistant TB may develop. Extensively drug-resistant TB, XDR-TB, is a form of multidrug-resistant TB with additional resistance to more anti-TB drugs that therefore responds to even fewer available medicines. It has been reported in 117 countries worldwide.

Drug resistance can be detected using special laboratory tests which test the bacteria for sensitivity to the drugs or detect resistance patterns. These tests can be molecular in type (such as Xpert MTB/RIF) or else culture-based. Molecular techniques can provide results within hours and have been successfully implemented even in low resource settings.

New WHO recommendations aim to speed up detection and improve treatment outcomes for MDR-TB through use of a novel rapid diagnostic test and a shorter, cheaper treatment regimen. At less than US$ 1000 per patient, the new treatment regimen can be completed in 9–12 months. Not only is it less expensive than current regimens, but it is also expected to improve outcomes and potentially decrease deaths due to better adherence to treatment and reduced loss to follow-up.

Solutions to control drug-resistant TB are to:

cure the TB patient the first time around

provide access to diagnosis

ensure adequate infection control in facilities where patients are treated

ensure the appropriate use of recommended second-line drugs.

In 2016, an estimated 490 000 people worldwide developed MDR-TB, and an additional 110 000 people with rifampicin-resistant TB were also newly eligible for MDR-TB treatment. The countries with the largest numbers of MDR/RR-TB cases (47% of the global total) were China, India and the Russian Federation. It is estimated that about 6.2% of these cases were XDR-TB.

Polio is a disease you read about in history books. Does it still exist? Is it curable?

Polio does still exist, although polio cases have decreased by over 99% since 1988, from an estimated more than 350 000 cases to 22 reported cases in 2017. This reduction is the result of the global effort to eradicate the disease. Today, only 3 countries in the world have never stopped transmission of polio (Pakistan, Afghanistan and Nigeria).

Despite the progress achieved since 1988, as long as a single child remains infected with poliovirus, children in all countries are at risk of contracting the disease. The poliovirus can easily be imported into a polio-free country and can spread rapidly amongst unimmunized populations. Failure to eradicate polio could result in as many as 200 000 new cases every year, within 10 years, all over the world.

There is no cure for polio, it can only be prevented. Polio vaccine, given multiple times, can protect a child for life.

What is hepatitis B?

Hepatitis B is a liver disease caused by the hepatitis B virus (HBV). The virus interferes with the functions of the liver and causes pathological damage. A small percentage of infected people cannot get rid of the virus and become chronically infected – these people are at higher risk of death from cirrhosis of the liver and liver cancer.

How do you get hepatitis B?

HBV is spread by contact with blood or body fluids of an infected person – the same way as the human immunodeficiency virus (HIV). However, HBV is 50 to 100 times more infectious than HIV.

The main ways of getting infected with HBV are:

from mother to baby at the birth (perinatal)

from child-to-child

unsafe injections and transfusions

unprotected sexual contact.

Worldwide, most infections occur from mother-to-child, from child-to-child (especially in household settings), and from reuse of unsterilized needles and syringes. Before the widespread use of the hepatitis B vaccine, almost all children in developing countries used to become infected with the virus.

How is Hepatitis B NOT spread?

Hepatitis B virus is NOT spread by sharing eating utensils, breastfeeding, hugging, kissing, holding hands, coughing, sneezing or by recreational use of public pools or the like.

How can I protect myself?

You can protect yourself against hepatitis B by being vaccinated. The hepatitis B vaccine has an outstanding record of safety and effectiveness, and since 1982, over 1 billion doses have been used worldwide. The vaccine is 95% effective in preventing chronic infections from developing. Protection lasts for 20 years at least, no booster is recommended by WHO as of today.

What is vaccine-derived polio?

Oral polio vaccine (OPV) contains an attenuated (weakened) vaccine-virus, activating an immune response in the body. When a child is immunized with OPV, the weakened vaccine-virus replicates in the intestine for a limited period, thereby developing immunity by building up antibodies. During this time, the vaccine-virus is also excreted. In areas of inadequate sanitation, this excreted vaccine-virus can spread in the immediate community (and this can offer protection to other children through ‘passive’ immunization), before eventually dying out.

On rare occasions, if a population is seriously under-immunized, an excreted vaccine-virus can continue to circulate for an extended period of time. The longer it is allowed to survive, the more genetic changes it undergoes. In very rare instances, the vaccine-virus can genetically change into a form that can paralyse – this is what is known as a circulating vaccine-derived poliovirus (cVDPV).

It takes a long time for a cVDPV to occur. Generally, the strain will have been allowed to circulate in an un- or under-immunized population for a period of at least 12 months. Circulating VDPVs occur when routine or supplementary immunization activities (SIAs) are poorly conducted and a population is left susceptible to poliovirus, whether from vaccine-derived or wild poliovirus. Hence, the problem is not with the vaccine itself, but low vaccination coverage. If a population is fully immunized, they will be protected against both vaccine-derived and wild polioviruses.

Since 2000, more than 10 billion doses of OPV have been administered to nearly 3 billion children worldwide. As a result, more than 13 million cases of polio have been prevented, and the disease has been reduced by more than 99%. During that time, 24 cVDPV outbreaks occurred in 21 countries, resulting in fewer than 760 VDPV cases.

Until 2015, over 90% of cVDPV cases were due to the type 2 component in OPV. With the transmission of wild poliovirus type 2 already successfully interrupted since 1999, in April 2016 a switch was implemented from trivalent OPV to bivalent OPV in routine immunization programmes. The removal of the type 2 component of OPV is associated with significant public health benefits, including a reduction of the risk of cases of cVDPV2.

The small risk of cVDPVs pales in significance to the tremendous public health benefits associated with OPV. Every year, hundreds of thousands of cases due to wild polio virus are prevented. Well over 10 million cases have been averted since large-scale administration of OPV began 20 years ago.

Circulating VDPVs in the past have been rapidly stopped with 2–3 rounds of high-quality immunization campaigns. The solution is the same for all polio outbreaks: immunize every child several times with the oral vaccine to stop polio transmission, regardless of the origin of the virus.

Do all mosquitoes transmit malaria?

Only certain species of mosquitoes of the Anopheles genus—and only females of those species—can transmit malaria.

Malaria is caused by a one-celled parasite called a Plasmodium. Female Anopheles mosquitoes pick up the parasite from infected people when they bite to obtain blood needed to nurture their eggs. Inside the mosquito the parasites reproduce and develop. When the mosquito bites again, the parasites contained in the salivary gland are injected and pass into the blood of the person being bitten.

Malaria parasites multiply rapidly in the liver and then in red blood cells of the infected person. One to two weeks after a person is infected the first symptoms of malaria appear: usually fever, headache, chills and vomiting. If not treated promptly with effective medicines, malaria can kill by infecting and destroying red blood cells and by clogging the capillaries that carry blood to the brain or other vital organs.

There are four types of human malaria: Plasmodium vivax, P. malariae, P. ovale and P. falciparum. P. vivaxand P. falciparum are the most common forms. Falciparum malaria—the most deadly type—is most common in sub-Saharan Africa, where it causes more than 400 000 deaths a year.

In recent years, some human cases of malaria have also occurred with Plasmodium knowlesi – a species that causes malaria among monkeys and occurs in certain forested areas of South-East Asia.

What is dengue and how is it treated?

Dengue is a viral infection transmitted by the bite of an infected female Aedes mosquito. There are four distinct serotypes of the dengue virus (DEN 1, DEN 2, DEN 3 and DEN 4). Symptoms appear in 3–14 days (average 4–7 days) after the infective bite. Dengue fever is a flu-like illness that affects infants, young children and adults.

There is no specific treatment for dengue fever. Severe dengue is a potentially lethal complication but early clinical diagnosis and careful clinical management by experienced physicians and nurses often save lives.

More than 70% of the disease burden is in South-East Asia and the Western Pacific. In Latin America and the Caribbean, the incidence and severity of disease have increased rapidly in recent years. The African and Eastern Mediterranean regions have also recorded more outbreaks of the disease in the last ten years. Since 2010 indigenous transmission of dengue has also been reported in Europe. Urbanization, rapid movement of people and goods, favorable climatic conditions and lack of trained staff have all contributed to the global increase of dengue.

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Editor : M. Shamsur Rahman

Published by the Editor on behalf of Independent Publications Limited at Media Printers, 446/H, Tejgaon I/A, Dhaka-1215.
Editorial, News & Commercial Offices : Beximco Media Complex, 149-150 Tejgaon I/A, Dhaka-1208, Bangladesh. GPO Box No. 934, Dhaka-1000.

Editor : M. Shamsur Rahman
Published by the Editor on behalf of Independent Publications Limited at Media Printers, 446/H, Tejgaon I/A, Dhaka-1215.
Editorial, News & Commercial Offices : Beximco Media Complex, 149-150 Tejgaon I/A, Dhaka-1208, Bangladesh. GPO Box No. 934, Dhaka-1000.

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