Lassa virus has thousand-year history in Nigeria

Lassa virus (LASV) genome sequences have revealed that the although the virus was only discovered in 1969, it originated more than a thousand years ago in present-day Nigeria and continues to undergo significant evolutionary change, according to a National Institutes of Health (NIH)–funded study yesterday in Cell.

LASV, which causes the highly lethal hemorrhagic Lassa fever in humans, is endemic in West Africa and causes several thousand deaths in the region each year. The prior availability of only 12 complete LASV genomes has limited study of the virus's origin, host-reservoir interactions, and ongoing evolution.

The present study's authors sequenced 183 LASV genomes obtained from Lassa fever patients admitted to Sierra Leone's Kenema Government Hospital and Nigeria's Irrua Specialist Teaching Hospital between 2008 and 2013, 11 genomes from the LASV rodent reservoir Mastomys natalensis (natal multimammate mouse), and 2 from laboratory isolates.

Molecular dating revealed that LASV originated in the area that is now Nigeria more than a thousand years ago and spread into present-day Sierra Leone, Guinea, and Liberia within the last several hundred years, undergoing significant evolutionary change during its migration.

In an analysis of 169 sequences of human genomic material, only 5 (3%) clustered on the phylogenetic tree, in comparison with 5 of 10 (50%) rodent sequences, indicating that human-to-human LASV transmission is probably the exception rather than the rule. Most LASV infections likely result from direct interactions between M natalensis and humans, and the virus's genetic diversity owes much to its persistence within the rodent reservoir.

Researchers also found evidence that LASV continues to undergo significant evolution within its rodent reservoir and in human hosts, noting that adaptation in one mammal leads to adaptation in the other. Mutations in the epitopes of viral surface proteins where antibodies bind indicate that LASV is evolving ways aimed at evading immune system recognition.

The study highlights the importance of monitoring LASV's genetic diversity, host-reservoir interactions, and mutational activity to develop better preventive and therapeutic methods for reducing illness and death from Lassa fever.
Aug 13 Cell study abstract

Lyme disease incidence high among young boys and older adults

The incidence of Lyme disease diagnoses and inpatient visits in the United States is likely higher than previous surveillance data have estimated, especially among young boys and older adults, according to a study in the September issue of Emerging Infectious Diseases.

Researchers from the Centers for Disease Control and Prevention (CDC) compared surveillance data to provider information on outpatient visits and inpatient admissions submitted to a national health insurance claims database between 2005 and 2010. The database represents about 27 million people under the age of 65 with employer-provided health insurance.

Providers reported 985 inpatient admissions and 44,445 outpatient diagnoses of Lyme disease during the time period. The annual incidence of Lyme disease was extrapolated to be 107 cases per 100,000 persons, resulting in approximately 329,000 cases annually.

Both inpatient and outpatient cases peaked in number during the summer months, comprising 62% and 50% of average annual Lyme disease cases. Fifteen states, all in the Northeast except for Minnesota and Wisconsin, reported 81% of Lyme disease cases.

Inpatient admissions were highest for boys 5 to 9 years old (1.8 admissions per 100,000 population) and men aged 60 to 64 (1.9 admissions per 100,000). Outpatient diagnoses were highest for boys 5 to 9 years of age (54.5 cases per 100,000) and women 60 to 64 (54.7 cases per 100,000).

Researchers also found that the incidence for Lyme disease diagnoses was higher than expected among women 15 to 34 years old when compared with national surveillance data.

Lyme disease is the fifth most commonly reported nationally notifiable disease in the United States, and variable incidence data submitted by providers and state health officials suggest that cases may be significantly underreported.
Sep 2015 Emerg Infect Dis study

Varicella outpatient visits, hospitalizations continue ebb as program matures

As immunization against varicella (chickenpox) has become routine and increasing numbers of individuals receive a 2-dose regimen, outpatient visits and hospitalizations for the illness as of 2012 decreased 84% and 93% over prevaccination rates, says a study published Aug 12 in the Journal of the Pediatric Infectious Diseases Society.

A 1-dose regimen was introduced in 1996 that met with a 59% decline in outpatient visits for varicella and an 88% decline in hospitalizations in 2002 over the prevaccination period (1994-95), note the authors, who are from the Centers for Disease Control and Prevention (CDC). The higher, new numbers include further declines since the introduction of the 2-dose regimen in 2007.

The researchers carried out a retrospective cohort study based on claims data in Truven Health MarketScan databases from 1994 to 2012. Overall varicella outpatient visits declined from an average of 215 to an average of 33 per 100,000 population from the prevaccination period to 2012 (84%, P < 0.001), with 78% and 22% of the decline occurring during the 1-dose and the 2-dose periods, respectively. Overall varicella hospitalization rates declined from an average of 2.35 to 0.16 per 100,000 (93%, P < 0.001), with 89% and 11% occurring during the 1- and 2-dose periods, respectively.

The largest declines in both outpatient visits and hospitalizations over the study period were seen in children and adolescents 1 to 19 years of age, which is the age-group targeted for vaccination, say the authors.

"After 16 years, the varicella vaccination program continues to mature and to provide increasing beneficial national impact," conclude the researchers.
Aug 12 J Pediatric Infect Dis Soc study abstract

Agreement clears way for Japan's first BSL-4 lab

Japan is upgrading an existing lab near Tokyo to create the country's first biosafety level 4 (BSL-4) lab, capable of handling the world's most dangerous pathogens, Nature reported yesterday. An agreement between Japan's health ministry and the mayor of the city of Musashi-Murayama was the final hurdle in 30 years of opposition to the lab, which is located about 18 miles west of Tokyo.

The agreement allows limited work to begin with BSL-4 pathogens such as Lassa and Ebola viruses, according to the Nature report. The country's National Institute of Infectious Diseases built a BSL-4 lab in 1981, but safety concerns limited the facility to BSL-3 work.

The agreement was partly triggered by Ebola concerns and stipulates that the work must be limited to diagnosing and treating patients, rather than broader research, Nature reported. However, some scientists said they hoped the step would lead to an expansion of BSL-4 basic research in the future and that plans are in the works for a more modern facility at Nagasaki University, where community members oppose the lab, the report said.
Aug 14 Nature news story