Infectious diseases – AIDS

ACQUIRED IMMUNODEFICIENCY SYNDROME (AIDS)

• caused by HIV;
• the virus infects and destroys cells of the body‘s immune system (T-cells that control the body‘s immune response to infection) so that their numbers gradually decrease;
•  when their numbers are low, the body is unable to defend itself against infection, so allowing a range of parasites to cause a variety of different infections (known as opportunistic infections);
• AIDS is not a disease but it is a collection of rare opportunistic diseases associated with immunodeficiency caused by HIV infection;
• since HIV is an infective agent; AIDS is called an acquired immunodeficiency to distinguish it from other types, for example an inherited form;

 

Structure of the HIV virus

• the outer envelope contains two glycoproteins gp120 and gp 41;
• the protein core contains the genetic material (RNA) and two enzymes, protease and reverse transcriptase;
• reverse transcriptase uses the RNA as a template to produce DNA once the virus is inside a host cell;

Transmission

• in semen and vaginal fluid during sexual intercourse;
• infected blood or blood products;
• contaminated hypodermic syringes;
• mother to fetus across placenta;
• mother to infant in breast milk;
• HIV is a virus that is spread by intimate human contact: there is no vector and the virus is unable to survive outside the human body;
• sexual intercourse is the main method of transmission;
• the initial epidemic in North America and Europe was amongst male homosexuals who had many sex partners and practised anal intercourse;
• the mucus lining of the rectum is not as thick as that lining of the vagina;
• it is often damaged during intercourse and the virus passes from the semen to the blood;
• as many homosexuals were blood donors and also had heterosexual relationships, the virus spread more widely;
• at high risk of infection were haemophiliacs who were treated with clotting substance (factor 8) isolated from blood pooled from many donors;
• the transmission of HIV by heterosexual transmission is rising world wide

 

Viral Replication/Multiplication

• the virus binds to receptors present in the surface of the T4 lymphocytes;
• from here it enters the lymphocytes by endocytosis or by fusing with the cell surface membrane and injects its viral RNA directly into the cell;
• the viral RNA is then copied into DNA by the activity of the enzyme reverse transcriptase;
• the viral DNA enters the lymphocyte nucleus and becomes incorporated into the cell‘s own DNA;
• thus it becomes a permanent part of the cells of an infected individual;
• every time the human cell divides, so does the viral DNA, and thus spread of the viral genes is rapid;
• the viral DNA may remain dormant for at least six years, the so-called latency period;
• however suddenly, for some unknown reason, the lymphocytes begin to make some copies of the viral genes in the form of mRNA;
• these then migrate from the nucleus into the lymphocyte cytoplasm and direct the synthesis of viral proteins and RNA;
• these assemble to form the new HIV viruses which leave the lymphocyte by budding out from underneath the cell surface membrane;
• the viruses spread and infect many other lymphocytes and brain cells;
• eventually the cells in which the virus has multiplied and killed;

 

HIV and Immunity

• lymphocytes are very important white blood cells in the maintenance of normal immunity
• there are 2 types of lymphocytes in circulation- T and B lymphocytes
• B-lymphocytes are responsible for cellular immunity
• T- lymphocytes have a cluster of differentiation (CD) molecules receptors and co-receptors
• HIV attacks and destroys CD4 T- lymphocytes
• HIV also attaches to CNS, gut, and lymph nodes
• with the fall in CD4 lymphocyte count the individual becomes prone to opportunistic infections

 

HIV infection progression

–    the phases of HIV infection  include;

1. HIV infection.
2. Window period
3. Seroconversion
4. Asymptomatic HIV
5. HIV /AIDS related illnesses
6. AIDS

 

 

1. HIV Infection

• initial infection with HIV

2. Window period

• time lag between infection and detection of antibodies;
• rapid multiplication of virus;
• person highly infectious;
• no signs and symptoms of disease and no detectable HIV antibodies;
• last 2-6 weeks or occasionally months;

 

3. Seroconversion (antibody – positive phase/ HIV-positive phase)

• the development of antibodies to HIV;
• part of the immune response;
• when people develop antibodies to HIV, they “seroconvert” from antibody-negative to antibodypositive;
• a brief phase occurring 2-6 weeks up to a few months of exposure;
• develop;
• may be accompanied by flu-like illness, such as fever, head ache, muscle and joint aches, sore throat, rash and diarrhea or rarely encephalitis with severe headache;
• may be called ACUTE HIV SYNDROME;

 

4. Asymptomatic HIV

• lasts from one year to 10-15 years or more;
• antibodies present but no apparent symptoms;
• this is the incubation period which may be accompanied by persistent generalized lymphadenopathy (PGL) lasting for a long time without other disease symptoms;

 

5. HIV related illnesses (AIDS –related complex)

• lasts months to years;
• signs and symptoms increase because HIV is damaging the immune system;
• the individual may contract a variety of conditions known as opportunistic infections;
• symptoms are not life-threatening but become more serious and long lasting;
• common bacterial, viral and fungal infections occur and are often noted for their persistence and virulence;
• oral and genital herpes or athlete‘s foot are common examples;
• if a person goes into ARC the duration of this type of infection is lengthened compared with that in a normal healthy person;
• loss of weight may be seen at this stage;
• a significant drop occurs in the number of T helper cells;
• appropriate nursing is required since this stage is the first real onset of the disease diagnosis;

 

6. AIDS

• lasts usually less than one year unless treatment is available;
• terminal stage;
• life threatening infections and cancers occur because the immune system is severely weakened and cannot cope;
• life expectancy depend on:
• the condition that develops;
• availability of treatment including ARVs, drugs for the treatment of other opportunistic infections; – good nutrition;
• availability of psychosocial support and holistic care;

 

Factors that affect progression

• infection with different types of HIV;
• natural genetic differences in individual immune system;
• stress on the immune system through a general lack of fitness and exposure to repeated or severe infections with different organisms;
• repeated STIs that keep the immune system highly active and so appear to speed up HIV replication;
• state of mind;
• other stressors such as overtiredness, poor diet, under nutrition and heavy drinking of alcohol;

 

Global distribution

• worldwide especially in Africa and South- East Asia;

 

Explain the possible reasons for the global distribution of HIV/AIDS

• is a pandemic  disease (globally distributed)
• an epidemic (always present)
• most prevalent in developing countries
• linked to TB
• some of the TB strains becoming more resistant
• AIDS pandemic
• partial treatment of due to inability to purchase ARVs
• poor medical facilities
• Highly confined in sub-Saharan Africa
• Rates of infection are lower in other parts of the world, but different subtypes of the virus have spread to Europe, India, South and South-East Asia, Latin America, and the Caribbean. Rates of infection have leveled off somewhat in the United States and Europe.
• In Asia the sharpest increases in HIV infections are found in China, Indonesia, and Vietnam.
• Both the cost of these therapies and the poor health care delivery systems in many affected countries need to be addressed before antiretrovirals can benefit the majority of people living with HIV/AIDS.

 

Prevention and treatment of HIV/AIDS

• AIDS is caused by a virus and while bacteria can be controlled by antibiotics, these are not effective against viruses;
• most treatments are therefore limited to relieving symptoms;
• present research on treatment and prevention is concentrating on three areas;
• restoring or improving the damaged immune system;
• developing drugs that will stop the growth of the virus and also treat the other infections and symptoms that result from HIV infection;
• developing a vaccine against the virus; (iv) development of drugs

 

The other obvious precautions which can be followed in trying to prevent the disease are:

• use of a barrier during intercourse can prevent the virus from infecting through blood or semen. Thus the use of sheath or condom is recommended.
• restriction to one sexual partner and the absence of promiscuity will also clearly reduce the risk of infection;
• use of clean needles and syringes by drug addicts;
• testing blood donated for the presence of antibodies to HIV which indicates whether or not the donor is infected; blood containing these antibodies is not used;
• educating people about the disease particularly in reassuring the public about the real risks.
• contact tracing
• needle exchange schemes operate in some places to exchange used needles for sterile needles to reduce the chances of infection with HIV and other blood borne diseases;
• in developed countries, blood collected from blood donors is routinely screened for HIV and heat treated to kill any virus;
• people who think they may have been exposed to the virus are not encouraged to donate blood;
• HIV+ women are advised not to breast feed their children because of the risk of transmitting the virus to their child because both viral particles and infected lymphocytes are found in breast milk ;

 

Social and economic factors in the prevention of HIV AIDS

• HIV transmitted by sexual intercourse with infected person/mother to child;
• education on ways of preventing transmission is important;
• education in work places on methods of preventing the spread of HIV;
• education on use of condoms to reduce risk of infection during intercourse
• sharing unsterilized needles among illicit drug users;
• injecting drug users can be advised not to share needles;
• sharp instruments like razors/shaving machines must not be shared;
• HIV+ not willing to disclose status/unwilling to go for testing;
• fear of stigmatization by society
• ARVs available but not affordable to all;
• prostitution due to poverty;
• polygamy/promiscuity;
• Government to inject more money in awareness campaigns;
• HIV+ women (in developing countries) can be advised not to breastfeed;
• HIV+ women to take antiretroviral drugs (navirapine) before delivery;
• Blood collected from blood donors routinely screened for HIV and heat treated to kill any viruses;