Chair of Microbiology, Virology, and Immunology

Lecturer Prof. S.I. Klymnyuk

Retroviridae. Human Immunodeficiency

Virus

The first indication of new disease – Acquired Immunodificiency Syndrom (AIDS) began in the summer of 1979, when reports came from great city of USA (New York, Los Angeles, San Francisco) of a sudden increase in the incidence of two very rare diseases Kaposi's sarcoma (before registrated only at elderly Africans) and Pneumocystis carinii pneumonia (before described as epidemics at the closed children’s establishments) in young adults who were homosexuals or addicted to heroin or other injected narcotics. They appeared to have lost their immnune competence, rendering them vulnerable to overwhelming and fatal infections with relatively avirulent microorganisms, as well as to lymphoid and other malignancies.

Pneumocystis carinii

StatisticsStatistics

• The latest statistics on the world The latest statistics on the world epidemic(UNAIDS/WHO) - 2005epidemic(UNAIDS/WHO) - 2005

• People living with HIV/AIDS 36,6 millionPeople living with HIV/AIDS 36,6 million• Adults living with HIV/AIDS 36,3 millionAdults living with HIV/AIDS 36,3 million• Women living with HIV/AIDS 17,3millionWomen living with HIV/AIDS 17,3million• Children living with HIV/AIDS 2,3 millionChildren living with HIV/AIDS 2,3 million• New infections with HIV/AIDS 4,1 millionNew infections with HIV/AIDS 4,1 million• AIDS deaths in 2005 2,8 millionAIDS deaths in 2005 2,8 million

Every day in the world infect with HIV 14.000 people, about 6.000 – young men and women 15 - 24 years old.

New infections

Adults and children estimated to be living with Adults and children estimated to be living with HIV/AIDS (2003)HIV/AIDS (2003): 34 – 46 million total

Western Europe520 000 – 680

000North Africa &

Middle East470 000 – 730

000Sub-Saharan Africa25.0 – 28.2 million

Eastern Europe & Central Asia1.2 – 1.8 million

South & South-East Asia4.6 – 8.2 million

Australia & New Zealand

12 000 – 18 000

North America790 000 – 1.2 million

Caribbean350 000 – 590

000Latin America

1.3 – 1.9 million

East Asia & Pacific700 000 – 1.3

million

HIV: A Global PandemicHIV: A Global PandemicHIV: A Global PandemicHIV: A Global Pandemic

Further statisticsFurther statistics

• 48% of adults living HIV/AIDS are women and 59% in the Sub-Saharan Africa

• 24,5 million of adults and children living with HIV is in the Sub-Saharan Africa

• Although the Sub-Saharan has just over 10% of the worlds population but it is close to two thirds of those who live with HIV/AIDS

NOTE:NOTE:

• More than 25 million people died of AIDS since 1981 and AFRICA has more than 12 million orphans

HIV, the etiologjcal agent of AIDS, belongs to the lentivirus subgroup of the family Retroviridae. The lentivirus subgroup (L. lentus = slow) includes the causative agents of the slow virus diseases visna/maedi in sheep and others. Besides HIV, the related animal immunodeficiency viruses also are assigned to this group.

Types of HIV Virus

• HIV 1– Most common in sub-Saharan Africa and

throughout the world– Groups M, N, and O– Pandemic dominated by Group M

Group M comprised of subtypes A - J

• HIV 2– Most often found in West Central Africa, parts

of Europe and India

Viral genes and antigens. The genome of HIV contains the three structural genes (gag, pol and env) characteristic of all retroviruses, as well as other nonstructural and regulatory genes specific for the virus. The products of these genes, both structural and nonstructural, act as antigens. Sera of infected persons contain antibodies to them. Detection of these antigenes and antibodies is ofgreat value in the diagnosis and prognosis of HIV infections.

Possible Infections

Virus travels through Bloodstream

Proteins cut and packaged with RNA

Budding new viruses

AIDS virus attaches to a CD4 receptor

Killer t-cells destroy affected cells

Transcription

HIV attacks t-cells

Reverse Transcription

The pathogenesis of AIDS is dependent on the biology of HIV, e.g:

'Trojan horse' mechanism - virus escapes recognition by replication inside monocytes, from where it can spread to other tissues and other hosts. Latency - Lentiviruses do not show true latency (unlike Herpes viruses or lambda) but do have the capacity to control the expression of their genome by means of virus-encoded trans-acting regulatory proteins (tat and rev). Antigenic variation - new variants continually arise. In other Lentiviruses such as CAEV, each new antigenic variant results in a flare up of disease. May also occur in HIV and contribute to decline of immune system - 'ratcheting' mechanism due to increasing virus load?

Some of the immune abnormalities in HIV infection include:

Altered cytokine expression Decreased CTL and NK cell function Decreased humoral and proliferative response to antigens and mitogens Decreased MHC-II expression Decreased monocyte chemotaxis Depletion of CD4+ cells Impaired DTH reactions Lymphopenia Polyclonal B-cell activation

It is not clear how much of the pathology of AIDS is directly due to the virus and how much is caused by the immune system itself. There are numerous models which have been suggested to explain how HIV causes immune deficiency:

Evolution of Antibodies

Window Period

Window Period

• Time from initial infection with HIV until antibodies are detected by a single test

• Usually 3-8 weeks before antibodies are detected

• May test false-negative for HIV antibodies during this time period

• Can still pass the virus to others during this period

Disease Progression

• Severity of illness is determined by amount of virus in the body (increasing viral load) and the degree of immune suppression (decreasing CD4+ counts)

• As the CD4 count declines, the immune function decreases.

-blood -semen -vaginal fluid -breast milk

ACQUIRED DEFICIENCY SYNDICOME (AIDS) Clinical features of HIV infection. AIDS is only the last stage in the divide spectrum of clinica features in HIV infection. The natural evolution of HIV infection can be considered in the following stages: I. Acute HIV infection. Within a few weeks of infection with HIV, about 10-15 per cent of persons experience low grade fever, malaise, headache, 1ymphadenopathy, sometimes with rash and arthropathy resembling glandular fever.

2. Asymptomatic infection. All persons infected with HIV, whether they experience seroconversion illness or not, pass through a phase of symptom1ess infection; lasting for several months or years. They show positive HIV antibody tests during this phase and are infectious. In some, the infection may not progress any further, while in others it may lead to full brown AIDS, either directly or through cytopenias, minor opportunistic infection, persistent generalised lympnadenopathy or AIDS related complex (ARC) as described below.

3. Persistant Generalised Liphadenopathy (PGL).

This has been defined as the presence of enlarged lymph nodes, at least 1,0 cm, in diameter, in two or more noncontiguous extrainguinal sites, that persist for at least three months, in the absence of any current illness or medication that may cause lymphadenopathy. This by itself is benign but a proportion of the cases may progress to ARC or AIDS.

4. AIDS Related Complex (ARC). This group inc1udes patients with considerable immunodeficiency, suffering from various constitutional symptoms or having minor opportunistic infections. The typical constitutional symptoms are fatigue, unexplained fever, persistent diarrhea and parked weight loss of more than 10 per cent of body weight. The common opportunistic infections are oral candidiasis, herpes zoster, salmonellosis or tuberculosis. Generalized lyrnphadenopathy and splenomegaly are usually present. ARC patients are usually severely ill and many of them progress to AIDS in a few months.

5. AIDS. This is the end stage disease representing the irreversible breakdown of immune defense mechanisms, leaving the patient a prey to progressive opportunistic infections and malignancies. The clinical severity of AIDS varies with the type of infection or malignancy present. In early AIDS, many patients are ill only during episodes of infection which may respond to treatment. Between episodes they may be relatively well and able to resume normal life.

WHO HIV/AIDS Classification System

Stage I

Asymptomatic

Stage I

Asymptomatic

Stage IIMinor

Symptoms

Stage IIMinor

Symptoms

Stage IIIModerate

Symptoms

Stage IIIModerate

Symptoms

Stage IV

AIDS

Stage IV

AIDS

According to the system most affected patients present with various complaints, some of which are as follows:

A. The commonest presentation is with increasing dry cough, dyspnea and fever. In the USA and other Western countries, the characteristic pathogen initially was P. carinii but now M. tuberculosis or an atypical mycobacterium such as M. avium-intracellulare is more often responsible. In the developing countries, the most important pathogen is M. tuberculosis, with many strains being multidrug resistant. In fact the poor nations are facing a double epidemic, jointly with HIV and tuberculosis. Pneumonia may be viral (CMV) or fungal (cryptococcus, histoplasma). Recurrent pneumonia is considered to be indicative of AIDS.

Pneumocystis carinii

Histoplasma capsulatum

B. Gastrointestinal system. The mouth is often involved in AIDS, with thrush, herpetic stomatitis, gingivitis, Kaposi's sarcoma. Dysphagia may be due to esophageal candidiasis. A characteristic intestinal pathogen in AIDS is cryptosporidium. Salmonellae, mycobacteria, CMV or adenoviruses also frequently cause intestinal infections. Systemic strongyloidosis may occur. Chronic colitis is common in male homosexuals («gay bowel syndrome»), from which ameba, lamblia and a host of diarrheagenic bacteria have been reported.

Candidiasis

Cryptosporidium (intestinal epithelium)

Central nervous system: The typical CNS opportunistic infections are toxoplasmosis and cryptococcosis. Infections are also seen with CMV, herpes simplex, papovaviruses, mycobacteria, aspergillus and Candida. Lymphomas of the central nervous system are common. D. Malignancies: Kaposi's sarcoma is the characteristic lesion seen in male homosexuals. It is an indolent multifocal nonmetastasising is mucosal or cutaneous tumor, probably of endothelial origin. The other tumors commonly seen are lymphomas, both the Hodgkin and non Hodgkin types.

Cryptococcus neoformans (nervous system)

E. Cutaneous. Besides Kaposi's sarcoma, herpes lesions, candidiasis, xeroderma, seborrheic dermatitis, prurigo, folliculitis, impetigo and molluscum contagiosumn are common cutaneous lesions. The definition of AIDS has since been broadened to include all seropositive persons (irrespective of clinical manifestations) with CD4 T cell counts of less than 200 per mm3.

Dermatomycosis Herpes zoster

Dermatitis Herpes

Kaposi's sarcoma Kaposi's sarcoma

Warts

Sarcoma

Herpetic infection

Еczema

6. Dementia. HIV may cause direct cytopathogenic damage in tire central nervous system. It can cross the blood brain barrier and cause encepfialopathy leading to loss of higher functions, progressing to dementia.

7. Pediatric AIDS. About one third to one half the number of babies born to infected mothers are infected with HIV. Many of them may not survive for a year. Children may also acquire the infection from b1ood transfusions or blood products.

Laboratory diagnosis Laboratory procedures for the diagnosis of HIV infection include tests for immunodificiency as well as specific tests for HIV.A. Immunological tests. The following parameters help to establish the immunodeficiency in HIV infection:l . Total leucocyte and lymphocyte count to demonstrate leucopenia and a lymphocyte count usually below 2,000 /c.mm. 2. T cell subset assays. Absolute T4 cell count will be usually less than 200/c.mm. T4: T8 cell ratio is reversed. 3. Platelet count will show thrombocytopenia. 4. Raised IgG and IgA levels. 5. Diminished CMI as indicated by skin tests. 6. Lymph node biopsy showing profound abnorma1ities.

B. Specific tests for HIV infection. These inc1ude demonstration of HIV antigens and antibodies and isolation of the virus. I. Antigen detection. The time course of appearance of detectable antigens and antibodies after VIIV infection is generally as follows: Following a single massive infection, as by blood transfusion, the virus antigens (p24) may be detectable in blood after about two weeks. IgM antibodies appear in about 4-6 weeks, to be followed by IgG antibodies (Fig. 2).

2. Virus isolation. Once infected with HIV, a person remains infected for life. The virus is present in circulation and body fluids, mostly within the lymphocytes but some are also cell free. Virus titres are high early in infection, about a week before antibodies start appearing. Antibodies do not neutralize the virus and the two can coexist in the body.

3. Antibody detection. Demonstration of antibodies is the simplest and most widely employed technique for the diagnosis of HIV infection.

Karpas’ test is a slide immunoperoxidase reaction. HIV infected cells fixed on teflon coated slide wells are treated first with the test serum and then with horseradish peroxidase labelled antihuman globulin. Finally, a suitable substrate is added which gives a colour reaction if the test is positive. The test is simple and inexpensive but the evaluation is subjective.

Collection of blood

Blood keeper

IMMUNOPROPHYLAXIS Several approaches are being used to develop a vaccine for HIV. At present, there is no safe and effective HIV vaccine.Types of HIV vaccines1. Attenuated vaccines are made from genetically engineered strains lacking some crucial genes, so that the resulting virus causes a harmless infection. This approach has been tried successfully with simian immunodeficiency virus (SIV)2. Killed virus vaccines do not induce protective anti-SlV immunity in animal trials. However, killed virus vaccines may prevent the emergence of clinical disease:- Monkeys vaccinated with killed SIV vaccines are less likely to develop disease.- In humans, it has been proposed that vaccination with low doses of killed HIV enhances cellular immunity and favors (lie development of cell-mediated cytotoxicity. The benefits of therapeutic immunization in humans are not known. Evaluation is difficult because the end-point is a disease-free interval that is long and variable.

3. Recombinant viral particles made by inserting HIV glycoprotein genes in, for example, vaccinia-virus genomes induce neutralizing antibodies in animals. The overall effectiveness of recombinant vaccinia virus vaccines in humans has not been established4. Component vaccines have been prepared from isolated gpl20, polymerized gpl20, or gpl20 peptides representing more conserved regions (such as the CD4-binding domain)

Therapy of HIV Infection:Several distinct classes of drugs are now used to treat HIV infection: Nucleoside-Analog Reverse Transcriptase Inhibitors (NRTI). These drugs

inhibit viral RNA-dependent DNA polymerase (reverse transcriptase) and are incorporated into viral DNA (they are chain-terminating drugs). Zidovudine (ZDV, Retrovir) first approved in 1987 Didanosine (ddI, Videx) Zalcitabine (ddC, Hivid) Stavudine (d4T, Zerit) Lamivudine (3TC, Epivir)

Non-Nucleoside Reverse Transcriptase Inhibitors (NNRTIs). In contrast to NRTIs, NNRTIs are not incorporated into viral DNA; they inhibit HIV replication directly by binding non-competitively to reverse transcriptase. Nevirapine (Viramune) Delavirdine (Rescriptor)

Protease Inhibitors. These drugs are specific for the HIV-1 protease and competitively inhibit the enzyme, preventing the maturation of virions capable of infecting other cells. Saquinavir (Invirase) first approved in 1995 Ritonavir (Norvir) Indinavir (Crixivan) Nelfinavir (Viracept)