Tuberculosis and HIV

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Mycobacterium tuberculosis and Human Immunodeficiency Virus are both diseases that plague many developing countries. In fact, data from 2003 shows that there are approximately 11 million people worldwide infected with both diseases [[1]. Currently there is an extensive discourse on the relationship between the two diseases, and whether or not there is a correlation between their effects and multi-drug resistant tuberculosis. A closer look at this discourse may reveal new information about how to control and treat these diseases, and how to combat drug resistant strains of tuberculosis from developing.

Tuberculosis

Tuberculosis is caused by the bacteria called Mycobacterium tuberculosis. This bacterium is nonmotile and rod-shaped, 2-4 micrometers in length and 0.2-0.5 um in width (SEE FIGURE). Because this bacterium is classified as an obligate aerobe, it is commonly found in the lungs, however, complications in the kidneys, spine, and brain can arise [[2] Additionally,Mycobacterium tuberculosis has a generation time of 15-20 hours, and is an acid-fast bacteria due to its unique cell walls, which contain a high concentration of lipids, including mycolic acids. This high concentration of lipids allows the bacterium to be impermeable to many stains and resistant to antibiotics, acidic and alkaline compounds, osmotic lysis, and lethal oxidations. Multidrug-Resistant tuberculosis, otherwise known as MDR TB, develops when the bacterium is resistant to two or more of the common anti-tuberculosis drugs such as, isoniazied and rifampin [[3]. Tuberculosis is highly contagious and spreads through the airborne transfer of Mycobacterium tuberculosis from an infected individual to others (i.e. through coughing and sneezing).There are two distinctions, latent infection and disease, that are ascribed to tuberculosis. Latent infection means that an individual has been exposed to the bacterium, but the immune system is able to control the bacterial growth by releasing macrophages that prevent the bacteria from spreading, and consequently the disease from developing [[4]. These individuals are not contagious and do not experience any tuberculosis related symptoms, but will still test positive for tuberculosis. Tuberculosis disease, or active tuberculosis, occurs when the bacterium continues to multiply beyond the control of the immune system. White blood cells form granulomas, which then grow to form nodules. The bacteria grow in these granulomas, and eventually breach the granulomatous wall, from which the bacteria enter the lungs and divide rapidly [[4]. Individuals with the disease experience coughing up blood and sputum, coughing for three or more weeks, night sweats, pleurisy, weight loss, fatigue, fever, pain in the chest, and loss of appetite. Left untreated, tuberculosis can be fatal. Over 10,000 bacteria per ml of sputum are required in order to determine the presence of Mycobacterium tuberculosis in a sputum sample under 1000X magnification [[5]. In order to diagnose tuberculosis, a mantoux skin test is conducted, however additional diagnostic tools such as, chest x-rays and sputum cultures, are needed to determine if the infection is latent or not. Since the generation time of tuberculosis is lengthy, treatment includes a combination of antibiotics prescribed for 6-12 months. Certain antibiotics, such as rifabutin, are not used to treat individuals who also have HIV, especially those who are taking protease inhibitors (saquinavir) and non-nucleoside reverse transcriptase inhibitors (delavirdine) [[1]. Individuals who have latent tuberculosis and HIV are treated with isoniazid. This particular treatment prevents the tuberculosis from developing into a disease, however it can have adverse side effects on the liver. Individuals infected with tuberculosis disease receive a combination of antibiotics, including isoniazid, rifampin, ethambutol, and pyrazinamide. This combination decreases the chance of antibiotic resistance from developing.

Electron micrograph of the Ebola Zaire virus. This was the first photo ever taken of the virus, on 10/13/1976. By Dr. F.A. Murphy, now at U.C. Davis, then at the CDC.

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Legend/credit: Electron micrograph of the Ebola Zaire virus. This was the first photo ever taken of the virus, on 10/13/1976. By Dr. F.A. Murphy, now at U.C. Davis, then at the CDC.
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HIV

Human Immunodeficiency Virus, or HIV, attacks the immune system by destroying immune cells with the CD4 receptor protein on their cell surfaces. A normal CD4 cell count is between 600 and 1,200 cells per microliter of blood. Individuals with HIV will have a CD4 cell count of less than 600 cells per microliter of blood. When HIV progresses to AIDS, individuals will have a CD4 cell count of less than 200 cells per microliter of blood. Similarly to TB, HIV has a latency period where individuals appear asymptomatic. This period can last for several years, but symptoms that develop include swollen lymph nodes, fatigue, weight loss, frequent fevers and sweats, and persistent yeast infections and skin rashes. HIV is spread through bodily fluids such as, blood, semen, vaginal secretions, and breast milk [[1]. Contraction of the disease is likely to occur during unprotected sex, breastfeeding, vaginal births, and by sharing needles with an infected individual [[1]. This attack on the immune system highly increases the risk of individuals developing other infections [[1]. In fact, HIV is the biggest predisposing factor for tuberculosis, with 10 percent of HIV positive individuals infected. HIV significantly increases the risk of latent tuberculosis developing into active disease. According to the CDC, tuberculosis the leading causes of death among HIV infected individuals. HIV infected individuals who also have TB commonly experience extrapulmonary symptoms in the bones, joints, nervous system, and urinary tract when the infection spreads to other organs [[1]. If treatment is started early, HIV infected individuals have a good chance of recovering from TB. HIV treatment usually includes a combination of highly active antiretroviral therapy, fusion inhibitors, nucleoside reverse transcriptase inhibitors, protease inhibitors, and nucleoside reverse transcriptase inhibitors. Although treatment can suppress the virus, HIV is not yet curable.

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Studies on the Relationship Between Mycobacterium tuberculosis and HIV

The Natural Standard supports that tuberculosis causes HIV to replicate faster and exacerbates HIV infection whereas other studies contend that there is no significant relationship between HIV infection and tuberculosis [[1]. A sample of these studies will now be presented. Most of these studies rely on the examination of clustering, which is defined as “DNA fingerprinting analysis of insertion element IS6110 of the genome Mycobacterium tuberculosis [[6]. Individuals who are part of a cluster are infected with strains with identical DNA fingerprints [[6]. Sputum and blood samples obtained from 2100 patients in Chandigarh, India indicated a significant association between multidrug resistant tuberculosis and HIV. After applying a multivariable regression analysis, which controlled the effects of previous treatment status, age, and sex, the study revealed that there was a high number of MDR Mycobacterium tuberculosisin the HIV seropositive group compared to the HIV seronegative group, with a p-value of 0.05. This suggests that there is indeed a correlation between the two diseases. Additionally this study offers valuable information about the high prevalence of drug resistance Mycobacterium tuberculosis, which will be further discussed in section four [[7]. Furthermore, a large population-based molecular epidemiological study of tuberculosis in Northern Malawi, an area with high HIV prevalence, confirmed that HIV significantly increases the risk of developing tuberculosis after recent infection. This is founded on the association between HIV and clustering, which refers to patients with identical tuberculosis isolates. These isolates were genotyped using restriction-fragment-length polymorphism patterns. Not only were clustering rates found to be the highest in the world, which suggests high rates of recent tuberculosis transmission, but clustering was also common in patients who were also infected with HIV. The study concludes that HIV has a great impact on recently transmitted tuberculosis compared to its effect on reactivated tuberculosis [[8]. Another study also analyzed the correlation between TB clustering and HIV in order to determine whether HIV is associated with tuberculosis in individuals who were recently infected or in those who experienced reactivation of latent TB. This was done via a systematic review, which identified all studies focusing on TB clustering and HIV infection in communities with high HIV prevalence. The results of the review showed that clustering patterns were associated with recently transmitted tuberculosis rather than reactivated latent infection. This finding is important because it can impact how tuberculosis is treated in HIV endemic populations [[9]. Finally, an additional study revealed that there is a significant presence of HIV co-infection, of approximately 14.2%, in patients tested positive for tuberculosis. This study exposes the impact of this co-infection on antibiotic resistance and development of MDR TB (see section four) [[10]. Studies that examine the relationship between HIV and TB offer valuable insight on the impacts on drug resistance development. In contrast, other studies reveal that there is no significant difference in culture analysis between HIV positive or negative individuals with tuberculosis [[11]. Similarly to the studies presented in section 3, these studies used DNA restriction fragment length polymorphism analysis of Mycobacterium tuberculosis isolates in order to assess clustering in HIV positive and negative individuals. However, this study yields that there is no significant relationship (p value of 0.615) between clustered isolates and HIV status. Researches found minimal discrepancies in the level of DNA fingerprint diversity between HIV positive and negative individuals. This contrasts with other studies that show that individuals that are co-infected with HIV and TB do no associate with clustering compared to individuals who are only infected with TB. (page 13/20) [[12].
Include some current research in each topic, with at least one figure showing data.

Effects on Antibiotic Resistance

Although there is contention about the effects that tuberculosis and HIV have on each other, there is little dispute about the dire consequences of antibiotic resistance. The CDC states that drug resistance develops in individuals who don’t take their medications regularly or correctly, develop tuberculosis after having taken medication for it in the past, and are in close contact with people who have drug-resistant tuberculosis (i.e. in hospital settings). Aside from multi-drug resistant tuberculosis, there is also extensively drug-resistant tuberculosis, otherwise known as XDR TB [[13]. XDR TB is more severe than MDR TB, and occurs when individuals are resistant to the most potent first and second line TB drugs available [[13]. These conditions highly increase the risk dying in individuals who are HIV positive. HIV positive individuals are predisposed to developing TB and to fast disease development due to their weakened immune systems [[3]. In addition to antibiotic resistance developing, studies show that co-administration tuberculosis and HIV medications may have adverse effects on individuals due to pharmacokinetic interactions, toxicity, and immune reconstitution inflammatory syndrome [[14] Pharmacokinetic interactions include how well the drugs are absorbed by individuals with advanced HIV and how the drugs interact together. Drug absorption is problematic because studies show that individuals who absorb a lower concentration of drugs such as, rifabutin and isoniazid, are more likely to develop rifamycin resistance. Additionally, other studies show that HIV co-infection is associated with rifampicin resistance [[10]. Further research suggests that HIV is closely associated with HIV, with a significant number (p value of 0.05) of MDR TB isolates found in cultures from HIV positive individuals (27.3%) compared to the number found in HIV negative individuals (15.4%) [[7]. However, some studies show that HIV does not have significant effects on MDR TB development based on there being no difference found in sputum cultures of HIV positive and negative individuals with MDR TB [[15]. Instead, these studies propose that MDR TB is greatly impacted by previous antibiotic treatment, with individuals who have had previous treatment being five times more likely to develop MDR TB [[11].

Concluding Remarks

The discourse on the interactions of tuberculosis and HIV yields that more research needs to be done in order to more thoroughly assess the impacts the diseases have on each other and on antibiotic resistance. So far, there is significant evidence that HIV affects recently transmitted tuberculosis more that latent infection. This means that greater care needs to be taken to prevent HIV patients, especially those with high viral loads, from being exposed to Mycobacterium tuberculosis. This can be difficult because there are high rates of coexistence of these diseases in developing countries, and HIV patients are often exposed to the bacterium in hospital settings. Additionally, there is a high prevalence of multi-drug resistant tuberculosis in HIV positive patients, which further implicates the interactions of these diseases in adverse drug interactions and resistance. More research could reveal what drug combinations could be most effective for the patient by limiting these drug interactions and resistance. Although there is contention amongst this discourse, each study offers invaluable insights into these serious, life-threatening diseases, which will only further the efforts to treat and eventually eliminate them.

Further Reading

[1]-National Center of Allergy and Infectious Diseases

References

[Sample reference] Takai, K., Sugai, A., Itoh, T., and Horikoshi, K. "Palaeococcus ferrophilus gen. nov., sp. nov., a barophilic, hyperthermophilic archaeon from a deep-sea hydrothermal vent chimney". International Journal of Systematic and Evolutionary Microbiology. 2000. Volume 50. p. 489-500.

Edited by (your name here), a student of Nora Sullivan in BIOL168L (Microbiology) in The Keck Science Department of the Claremont Colleges Spring 2014.