September 2018

Emerging Infectious Diseases

Highlights: Emerging Infectious Diseases, Vol. 24, No. 9, September 2018

Important Note: Not all articles that EID publishes represent work done at CDC or by CDC staff. In your stories, please clarify whether a study was conducted by CDC (“a CDC study”) or by another institution (“a study published by CDC in the EID journal”). Opinions expressed by authors contributing to EID do not necessarily reflect the opinions of CDC or the institutions with which the authors are affiliated.

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1.      Molecular Confirmation of Rocky Mountain Spotted Fever Epidemic Agent in Mexicali, Mexico, Luis Tinoco-Gracia et al.

Rocky Mountain spotted fever (RMSF) is a bacterial disease spread through the bite of an infected tick. RMSF can be deadly if not treated early with the right antibiotic. Most cases in the United States have been transmitted by bites of infected Dermacentor spp. ticks; however, recent epidemics along the US–Mexico border have been associated with bites of brown dog ticks (Rhipicephalus sanguineus). Although the brown dog ticks prefer to live and feed on dogs, they are capable of surviving indoors and will bite people. Beginning in the early 2000s, areas of northern Mexico, including Mexicali, began experiencing epidemic rates of RMSF, with case counts in the thousands and case fatality rates approaching 40% in some areas. Outbreaks in these areas are driven by large populations of brown dog ticks, free-roaming dog populations, and are concentrated in poorer communities. Since 2008, a border epidemic of RMSF has caused the deaths of 134 people in Mexicali and one in the United States. Human diagnostic samples from this outbreak were recently tested using molecular methods and confirmed the presence of Rickettsia rickettsii, the bacteria that causes RMSF. This effort, led by UC Davis School of Vet Med and Autonomous University of Baja California, produced the first sequencing of human diagnostic samples resulting from the 2008 outbreak in Mexicali. Efforts to prevent spread of RMSF in smaller, localized outbreaks include decreasing dog populations through spay and neuter programs, treating houses for ticks, and using long-acting tick collars on dogs. However, the large epidemic in a major city like Mexicali will require a far greater and more creative public health response.

Contact: Kat Kerlin, UC Davis News and Media Relations, (530) 752-7704, kekerlin@ucdavis.edu

2.    Travel-Associated Zika Cases and Threat of Local Transmission during Global Outbreak, California, USA, Charsey Cole Porse et al.

In less than a year after cases of Zika virus infection were reported from Brazil, the virus spread across South America, Central America, the Caribbean, and parts of Mexico. As is common for other mosquitoborne diseases, infections were eventually detected in Florida and Texas, USA. Another state where public health officials are concerned about Zika virus infection is California. Because California has a growing number of the mosquitoes that transmit this virus (Aedes mosquitoes), and because California borders Mexico, where Zika virus is common, researchers explored the extent of infection in this state. Their review of all cases reported to the California Department of Public Health during November 2015–September 2017 found 588 cases associated with travel to Zika virus–affected areas (especially Mexico and Central America). They also used mosquito surveillance data to map mosquito locations and found that Aedes mosquitoes had expanded into 12 additional counties in California. Although Zika virus transmission and Zika case numbers have decreased across the Americas, continued, limited, local transmission is expected. The risk for transmission in California, albeit low, is a continuing threat. Healthcare providers should be aware of the possibility of this infection in travelers and pay special attention to pregnant women returning from Zika virus–affected areas.

Contact: California Department of Public Health, Office of Public Affairs, email:cdphpress@cdph.ca.gov phone: (916) 440-7259

3.      From Culturomics to Clinical Microbiology and Forward, Grégory Dubourg et al.

Culturomics is the combined use of 3 components of microbiological research to discover new species of bacteria. The first component consists of high-throughput culture techniques, which are the use of automation equipment to grow cultures from a vast number of microorganisms—a feat that had proven impossible with the use of conventional techniques. The second component is matrix-assisted laser desorption/ionization time-of-flight mass spectrometry, better known as MALDI-TOF mass spectrometry, which is an extremely fast and cost-effective way of genetically identifying the bacterial colonies produced by high-throughput culture. The third component is a technique called 16S rDNA gene sequencing, which is used to confirm novel or unusual findings of MALDI-TOF mass spectrometry. By using culturomics, microbiologists in France were able to add 672 previously unidentified bacteria to the known number of bacteria in the human microbiome (i.e., the bacteria inhabiting the human mucosa, which consists primarily of mucus membranes in the nose, mouth, and gut). Because some of these otherwise harmless bacteria living in humans might also be involved in opportunistic infections, expanding the “bacterial repertoire” associated with humans could considerably increase the number of bacteria associated with human diseases. During the 5-year study period, in fact, the researchers found that without the use of culturomics, nearly 3% of all identified bacteria associated with human infections would not have been identified. Culturomics has promise for improving the accuracy of diagnosis of infectious diseases involving bacteria and for prompting appropriate medical interventions directed at the human microbiome.

Contact: Didier Raoult, IHU Méditerranée Infection, 19-21 Boulevard Jean Moulin, 13385 Marseille CEDEX 5, France; email: didier.raoult@gmail.com.

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