Abstract:
Spotted fever group rickettsia (SFGR) can cause mild to fatal illness. The
early interaction between the host and rickettsia in skin is largely unknown, and the
pathogenesis of severe rickettsiosis remains an important topic. A surveillance of
SFGR infection by PCR of blood and skin biopsy specimens followed by sequencing
and immunohistochemical (IHC) detection was performed on patients with a recent
tick bite between 2013 and 2016. Humoral and cutaneous immunoprofiles were
evaluated in different SFGR cases by serum cytokine and chemokine detection, skin
IHC staining, and transcriptome sequencing (RNA-seq). A total of 111 SFGR cases
were identified, including 79 “Candidatus Rickettsia tarasevichiae,” 22 Rickettsia raoultii,
8 Rickettsia sibirica, and 2 Rickettsia heilongjiangensis cases. The sensitivity to detect
SFGR in skin biopsy specimens (9/24, 37.5%) was significantly higher than that
in blood samples (105/2,671, 3.9%) (P 0.05). As early as 1 day after the tick bite,
rickettsiae could be detected in the skin. R. sibirica infection was more severe than
“Ca. Rickettsia” and R. raoultii infections. Increased levels of serum interleukin-18 (IL-
18), IP10, and monokine induced by gamma interferon (MIG) and decreased levels of
IL-2 were observed in febrile patients infected with R. sibirica compared to those infected
with “Ca. Rickettsia.” RNA-seq and IHC staining could not discriminate between
SFGR-infected and uninfected tick bite skin lesions. However, the type I interferon
(IFN) response was differently expressed between R. sibirica and R. raoultii
infections at the cutaneous interface. It is concluded that skin biopsy specimens
were more reliable for the detection of SFGR infection in human patients although
the immunoprofile may be complicated by immunomodulators induced by the tick
bite.
