MicrobiologyBytes

Extensively drug-resistant (XDR) tuberculosis (TB) is defined as TB that is resistant to at least rifampin and isoniazid (multidrug resistant [MDR]), as well as to any member of the quinolone family and at least one second-line anti-TB injectable drug: kanamycin, capreomycin, or amikacin. According to the World Health Organization (WHO), XDR-TB has been reported in 57 countries and is a major concern for global health. The WHO Global Task Force on XDR-TB has recommended laboratory-based surveillance to better understand the prevalence of XDR TB in developing countries. However, surveillance data on XDR-TB from China remain scarce. Shandong Province is the second largest province in China, with a population of 94 million. Shandong Provincial Chest Hospital (SPCH) is the only provincial-level hospital specializing in TB clinical service and control. In collaboration with the SPCH TB reference laboratory, researchers retrospectively analyzed the drug-resistance profiles of a group of clinical Mycobacterium tuberculosis isolates to estimate the prevalence of XDR-TB in China.

32% of isolates resistant to more than one first-line drug; 10% isolates were multidrug resistant, and 2% were XDR. XDR-TB is of major concern in China.

Laboratory-based Surveillance of Extensively Drug-Resistant Tuberculosis, China. EID 17(3) March 2011
To estimate the prevalence of extensively drug-resistant tuberculosis (XDR TB) in China, we retrospectively analyzed drug-resistance profiles of 989 clinical Mycobacterium tuberculosis isolates. We found 319 (32.3%) isolates resistant to >1 first-line drugs; 107 (10.8%) isolates were multidrug resistant, of which 20 (18.7%) were XDR. XDR TB is of major concern in China.

Related:

• Extreme drug resistant tuberculosis (XDR-TB)
• XDR tuberculosis – implications for global public health.N Engl J Med. (2007) 356: 656–659

We all know that China is changing – fast. With the largest population in the world and the speed of urbanization, the potential for the spread of human immunodeficiency virus (HIV) is worrying. By some estimates, over a million people in China could be infected with HIV, but reliable figure on the prevalence of HIV/AIDS in China have always been hard to come by. The most recent data from CDC estimates that in 2007, an estimated 700,000 people in China were living with HIV. An estimated 50,000 new HIV infections and 20,000 deaths related to acquired immunodeficiency syndrome (AIDS) occurred in 2007, and an estimated 71% of persons with HIV infection were unaware of their HIV status. In 2007, 40% of those living with HIV had been infected through heterosexual transmission and 38% through injection-drug use (HIV Infection – Guangdong Province, China, 1997-2007. MMWR 58(15) 396-400 April 24, 2009).

Guangdong Province in southeastern China is the country’s most heavily populated region, with an estimated 76 million permanent residents and 17 million migrants. Guangdong has undergone rapid economic development in recent years. The number of HIV infections in Guangdong increased from 102 recorded in 1997 to 4,593 in 2007, although this increase is partly due to increased testing and surveillance. Among males classified by HIV transmission category, 82% of newly diagnosed infections were attributed to injection-drug use, and among females, 53% engaged in high-risk heterosexual conduct.

During the ten years from 1997-2007, an aggregated total of 22,571 newly diagnosed HIV cases were reported in Guangdong, 82% in males and 18% in females. Every year, injection-drug use was the most commonly reported HIV transmission category.

The recent increase in reported HIV cases attributed to high-risk heterosexual contact and the decline in cases attributed to injection-drug use might suggest a shift in Guangdong’s HIV epidemic similar to the national trend, in which heterosexual transmission is the main transmission category in China. In the central region of Guangdong Province, where approximately 80% of the province’s HIV cases were reported in 2007, rapid economic growth has led to an influx of migrant workers. Migrant women who lack appropriate job skills might seek to supplement their income by becoming sex workers, and migrant men living apart from their spouses might become clients of sex workers.

The findings in this report are subject to at least three limitations. First, large percentages of the data were missing key elements. For example, in approximately 22% of cases, the patient’s age group was unknown, and approximately 38% of patients were not classified by transmission category. Second, because definitions for sex worker and injection-drug user were institution based, verification was not possible. Finally, because HIV-positive people in China are required by law to report their names and national identification numbers, those consenting to HIV testing likely represent a sample that is biased in unpredictable ways.

More community-based sampling of populations at high risk are being planned to provide a more complete picture of the HIV epidemic in Guangdong. Surveillance methods should be redefined so that they rely less extensively on institutions and more accurately represent those populations at greatest risk. Finally, because an estimated 71% of people with HIV infection in China are unaware of their status, more HIV counseling and testing should be urgently provided.

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Related:

• The changing face of HIV in China. 2008 Nature 455: 609-11
• HIV treatment reduces death rates in Africa
• Why is HIV a pathogen?
• How does HIV cause AIDS?

Human disease attributable to variola virus (VARV), the etiologic agent of smallpox, has been reported in human populations for more than 2,000 years. VARV is unique among orthopoxviruses in that it is an exclusively human pathogen. Because it has a large, slowly evolving DNA genome, researchers were able to construct a phylogeny of VARV by analyzing single nucleotide polymorphisms (SNPs) from genome sequences of 47 VARV isolates with broad geographic distributions. The results reveal two primary VARV clades, which are likely to have diverged from an ancestral African rodent-borne variola-like virus either 16,000 or 68,000 years before present (YBP), depending on which historical records (East Asian or African) are used to calibrate the molecular clock. One primary clade was represented by the Asian VARV major strains, the more clinically severe form of smallpox, which spread from Asia either 400 or 1,600 YBP. The other primary clade included both alastrim minor, a phenotypically mild smallpox described from the Americas, and isolates from West Africa. This clade diverged from an ancestral VARV either 1,400 or 6,300 YBP.
Observations of smallpox-typical skin rashes on Egyptian mummies dating from 1100 to 1580 B.C. gave credibility to theories that ancient Egypt was an early (and perhaps the earliest) smallpox endemic region. However, smallpox researchers noted that “The most striking thing about smallpox is its absence from the books of the Old and New Testaments, and also from the literature of the Greeks and Romans. Such a serious disease as variola major is very unlikely to have escaped a description by Hippocrates if it existed.” Historical records from Asia describe evidence of smallpox-like disease in medical writings from ancient China (1122 B.C.) and India (as early as 1500 B.C.). The earliest unmistakable description of smallpox first appears in the 4th century A.D. in China, the 7th century A.D. in India and the Mediterranean, and the 10th century A.D. in southwestern Asia. These early Asian descriptions could indicate that pandemic smallpox originated in East Asia. Sequence analysis indicates that divergence between VARV and rodent poxviruses occurred from 16,000 YBP to 68,000 YBP, and that VARV seems to have evolved from a pathogen of African rodents and subsequently spread out of Africa.
On the origin of smallpox: Correlating variola phylogenics with historical smallpox records
PNAS USA 2007 104:15787-15792

What does this all mean?

• In spite of concerns about bioterrorism, smallpox is no longer a major human pathogen, but understanding the origin of this disease, which has been of major importance for most of human history, offers glimpses into how we might rapidly understand new emerging diseases as they appear.
• For a long time it has been generally believed the the most probable origin for smallpox virus was in Asia, but as with yellow fever and HIV, this new research seems to show that smallpox originally came out of Africa.