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Co-infection

It is not uncommon for people to be concurrently infected with more than one infectious disease. Co-infection with HIV and TB or malaria gained attention over the past decade, as public health experts have been working to prevent and effectively treat co-infections.

Of the countries burdened with neglected diseases, 74 percent are confronting two or more diseases; 28 percent grapple with six or more.¹
Sexually transmitted infections (STIs) can raise an individual’s chance of contracting HIV by 10-fold.^{2, 3}
Co-infection with visceral leishmaniasis and HIV is problematic in parts of southern Europe and is increasingly so in East Africa and Asia.¹
More research is needed to better understand how to treat individuals battling more than one infectious disease and about how to coordinate the distribution of multiple treatments to reduce logistical costs.

Embracing a more holistic view of infectious diseases is important for strengthening health systems. Training community health workers, nurses and doctors to simultaneously treat and screen individuals for multiple infectious diseases would reduce the cost of health care and improve the health of the world’s poorest people.

HIV & Tuberculosis
Since the early 1990s, the HIV/AIDS pandemic has transformed the tuberculosis epidemic. While people with latent TB (and no HIV infection) have a 10 percent lifetime risk of developing active TB, those with HIV and TB co-infection have a 50 percent lifetime risk of developing active TB. Yet, movements to integrate HIV and TB control have only appeared in recent years and scientists continue to investigate the intricacies of TB/HIV co-infection.^{5, 6}

In 2008, more than one-third of HIV infected individuals were infected with the TB bacteria. Of the 9.3 million new TB cases in 2007, 1.4 million were also living with HIV. In many parts of the world, TB is a leading killer of HIV infected individuals—500,000 HIV-positive TB patients died in 2007.^{4, 5}
The weakened immune system, caused by HIV, appears to be the main mechanism for the development of HIV-related tuberculosis – it activates the latent TB and allows it to flourish. Similarly, the presence of TB appears to increase the progress of HIV/AIDS.⁸

Estimated HIV Prevalence in Population
Newly Infected with Tuberculosis, 2006⁹

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Countries with high adult HIV prevalence typically have higher HIV prevalence among TB patients.⁵ Over the past two decades, HIV led to increases in new TB infections and deaths. In Africa, the recent decline of new TB infections in high-HIV prevalence countries may be related to the stabilization of the number of people living with HIV/AIDS.
- Twenty-two countries with 80 percent of the burden of TB have been designated high-burden countries (HBCs), many of which are African countries with high numbers of people living with HIV.
- Swaziland, Namibia, Lesotho, Zambia, Sierra Leone, Côte d’Ivoire and Malawi are among the top 15 countries with the highest rates of TB incidence, largely due to the susceptibility of HIV-infected individuals to TB.
TB/HIV co-infection is not only a concern for adults. In South Africa, nearly 25 percent of children with HIV in one study developed TB during the course of a year.⁶
Complications posed by TB/HIV co-infection underline the importance of having health systems that coordinate prevention and treatment of multiple diseases.
- Integrated services – the provision of TB skin tests and counseling to those newly diagnosed with HIV, and HIV tests for TB patients – are crucial to treating both diseases.
- In 2008, nearly 1.4 million TB patients were tested for HIV and accessed HIV prevention, treatment and care services.^{4, 9}
Treatment. Treatment of patients with TB/HIV is similar to patients with only TB, though it is increasingly difficult.¹⁰ One marked difference in treating TB is that thioacetazone is prohibited in patients with HIV. Treatment of children co-infected with TB/HIV requires more research.⁶
HIV and drug-resistant TB.¹⁰ Little is known about the intersection of HIV and drug-resistant strains of TB – beyond the difficulties in preventing co-infection, diagnosing both diseases and treating co-infected patients.
- Epidemiologists are currently gathering data on co-infection of HIV and drug-resistant forms of TB.¹¹ Research on drug resistance in children is also needed.
- Patients with HIV and drug-resistant TB have higher risks of adverse drug reactions and drug toxicity. Patients require increased monitoring by health providers.
- It is recommended that TB/HIV programs be well-established before adopting drug-resistant TB/HIV interventions.

HIV & Malaria
HIV and malaria cross paths in sub-Saharan Africa, the epicenter of both infections. Due to inadequate disease surveillance in this region, reliable estimates of those co-infected with HIV and malaria are not available.^{12, 13} HIV/AIDS weakens the body’s natural immune response to malaria; the biological response to malaria infection facilitates the advancement of HIV/AIDS.¹⁴

Children who contract malaria and develop anemia are at increased risk of contracting HIV through blood transfusions needed to treat the anemia. In Africa, 6 million units of blood are not properly screened for HIV/AIDS and up to 30 percent of potential donors may be HIV-positive.
In pregnant women, HIV infection increases the likelihood of becoming infected with malaria and of experiencing malaria-related anemia and illness. In addition, HIV infection can reduce the effectiveness of antimalarial drugs.
Unlike with TB, the effects of malaria on non-pregnant, HIV-positive adults are not as readily apparent and were not well understood until recently.¹⁵
- In regions with high malaria rates, most non-pregnant adults have become immune to further infection. However, those with advanced-AIDS are prone to malarial fevers and a higher presence of parasites.
- Outside of heavily malarious countries, those with HIV/AIDS are more vulnerable to severe and potentially fatal infection as adults, as their immune systems weaken.
- In Botswana, Zimbabwe, Swaziland, South Africa and Namibia, countries where malaria-related episodes are not common among children, the number of clinical malarious episodes have increased by 15–28 percent and deaths due to malaria by 52–114 percent.¹⁶

HIV, Malaria and TB Co-infection with Other Neglected Diseases
Infection with soil-transmitted helminthes, particularly ascaris and trichuris, and schistosomiasis, can weaken the immune response, rendering people more susceptible to HIV/AIDS, malaria and TB.^{17, 18} These parasitic worm infections can also exacerbate the gravity and occurrence of malarial fevers and increase the chances of developing anemia. Thus, controlling helminth infections can alleviate the burden of malaria and other infectious diseases, particularly for women and children.

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¹	World Health Organization. 2009. Neglected tropical diseases: hidden successes, emerging opportunities. Geneva: WHO. Available from: http://whqlibdoc.who.int/publications/2009/9789241598705_eng.pdf
²	World Health Organization. Sexually transmitted infections fact sheet no. 110.2007 (accessed January 2, 2008), Available from: www.who.int/mediacentre/factsheets/fs110/en/index.html
³	Chin J. 2007. The AIDS Pandemic: the collision of epidemiology with political correctness. Oxford: Radcliffe Publishing.
⁴	World Health Organization. 2009 Tuberculosis Facts (accessed November 18, 2009), Available from: www.who.int/tb/publications/2009/tbfactsheet_2009_one_page.pdf
⁵	World Health Organization. 2009. Global tuberculosis control: epidemiology, strategy, financing. Available from: www.who.int/tb/publications/global_report/2009/pdf/full_report.pdf
⁶	Bakare N, Miller V. 2007. HIV-TB co-infection: meeting the challenge. Report of the Forum for Collaborative HIV Research and TB/HIV Working Group of the Stop TB Partnership Symposium and Roundtable discussions on HIV/TB. July 22-23, 2007, Sydney Australia, report date: November 2, 2007.
⁷	2007 HIV/AIDS Implementers' Meeting Kigali, Rwanda. Available from: http://www.stoptb.org/wg/tb_hiv/assets/documents/MeetingDocs/Kigali%20Experience%20Sharing%20and%20follow-up%20meeting%20June%202007/Support%20documents/TBHIV%20roadmap%20Kigali%202007.ppt#257,1,Slide 1
⁸	World Health Organization. Frequently asked questions about TB and HIV. (accessed December 31, 2007), Available from: http://www.who.int/tb/challenges/hiv/faq/en/index.html
⁹	World Health Organization. TB/HIV Facts 2009 (accessed December 1, 2009), Available from: www.who.int/tb/challenges/hiv/factsheet_hivtb_2009.pdf
¹⁰	World Health Organization. 2006. Guidelines for the programmatic management of drug-resistant tuberculosis. Geneva: WHO.
¹¹	Aziz MA, Wright A, Laszlo A, De Muynck A, Portaels F, Van Deun A, et al. 2006. Epidemiology of antituberculosis drug resistance (the Global project on Anti-tuberculosis Drug Resistance Surveillance): an updated analysis. Lancet 368:2145-54.
¹²	UNAIDS, World Health Organization. 2007. AIDS epidemic update. Available from: http://data.unaids.org/pub/EPISlides/2007/2007_epiupdate_en.pdf
¹³	Breman J, Alilio M, Mills A. 2004. Conquering the intolerable burden of malaria: what's new, what's needed: a summary. American Journal of Tropical Medicine & Hygiene 71:1-15.
¹⁴	Hewitt K, Steketee RW, Mwapasa V, Whitworth J, French N. 2006. Interactions between HIV and malaria in non-pregnant adults: evidence and implications. AIDS 20(16):1993-2004.
¹⁵	Whitworth J. Malaria and HIV. HIV inSite knowledge base chapter. (accessed January 25, 2007), Available from: http://hivinsite.ucsf.edu/insite?page=kb-05-04-04
¹⁶	Korenromp EL, Williams BG, de Vlas SJ, Gouws E, Gilks CF, Ghys PD, et al. 2005. Malaria attributable to the HIV-1 epidemic, sub-Saharan Africa. Emerg Infect Dis 11(9).
¹⁷	Molyneux P, Hotez J, Fenwick A. 2005. Rapid-impact interventions: how a policy of integrated control for Africa's neglected tropical diseases could benefit the poor. PLoS Medicine 2(No 11 e336).
¹⁸	Brooker S, Akhwale WS, Pullan R, Estambale B, Clarke SE, Snow RW, et al. 2007. Epidemiology of plasmodium-helminth co-infection in Africa: populations at risk, potential impact on anemia, and prospects for combining control. Am J Trop Med Hyg 77(Suppl 6):88-98.

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