Tropical rickettsial illnesses associated with adverse pregnancy outcomes

A recent study from the Thai-Myanmar border highlights the severe and previously under-reported adverse impact of readily treatable tropical rickettsial illnesses, notably scrub typhus and murine typhus, on pregnancy outcomes, finding that more than one third of affected pregnancies resulted either in stillbirth or premature and/or low birth weight babies.

Conducted by Prof Rose McGready and Assoc. Prof Daniel Henry Paris from the Shoklo Malaria Research Unit (SMRU) in Mae Sot, Thailand, and the Mahidol Oxford Research Unit (MORU) in Bangkok, affiliated to Oxford University, UK, in collaboration with Prof John Antony Jude Prakash of the Dept. of Clinical Microbiology, Christian Medical College, Vellore, India, the study, "Pregnancy outcome in relation to treatment of Murine typhus and Scrub typhus infection: a fever cohort and a case series analysis", will be published in the November 20th, 2014 issue of PLOS Neglected Tropical Diseases.

Caused by bacteria and often acquired by mite, flea or tick bites, tropical rickettsial illnesses - mainly scrub typhus and murine typhus - are a very common cause of undifferentiated fever in parts of South-East Asia. Until this study, there has been little information on the true burden of scrub typhus and murine typhus on in South-East Asia, largely because commonly used blood tests are generally unavailable and not very accurate.

The study reviewed nearly 20 years of published literature and included the results of a pregnancy fever cohort from the Thai-Myanmar border, which found that for pregnant women with rickettsial infections, the proportion of poor neonatal outcome was 36%.

Overall, the proportion of miscarriage and poor neonatal outcomes were unexpectedly high at 17% (14/81) and 42% (28/67), respectively and an association between increased adverse outcomes and longer duration of fever (p=0.050, linear trend) was noted. Poor neonatal outcomes were observed with all antimicrobials prescribed, and the use of azithromycin, the currently recommended anti-rickettsial drug, was not significantly associated with improved (p=0.610).

The authors conclude that more collaborative studies that follow women through to pregnancy outcome are required to accelerate the slow pace of improvement in the understanding of rickettsial illness in tropical pregnancies.

According to the authors, "Many infections that predominate in low-income countries, such as malaria, tuberculosis, hepatitis and rickettsiosis, fail to be counted in the causes of maternal and neonatal mortality in part due to the difficulty of making the diagnosis and weakness in data collecting systems. While maternal mortality from sepsis is reported to be on the decrease with recommendations for improved sanitation, death from 'sepsis' in tropical countries may be more complex than it first appears due to undiagnosed tropical disease."

About the authors

Associated with the UK's Oxford University and based at MORU's research unit SMRU in Mae Sot, Thailand, Prof Rose McGready is a senior research physician with extensive experience and a long scientific track record in pregnancy studies, with a focus on malaria and other tropical infections.

Associated with the UK's Oxford University and based at MORU in Bangkok, Associate Prof Daniel H. Paris is a senior research physician and the co-ordinator for rickettsial research projects across an Asia-wide network. His major interests include all aspects of diagnostics and immune-pathophysiology of tropical rickettsiosis.

Prof John Antony Jude Prakash, a senior faculty member and immunologist in the Dept. of Clinical Microbiology, Christian Medical College, Vellore, Tamil Nadu, India, has a strong track record highlighting diagnostic difficulties, immunological markers of severity and pregnancy outcomes of scrub typhus (and other infections).

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