Friday, August 24, 2018

PRO/AH/EDR> Rocky Mountain spotted fever - Mexico: (BN) genetic confirmation

ROCKY MOUNTAIN SPOTTED FEVER - MEXICO: (BAJA CALIFORNIA) GENETIC
CONFIRMATION
*****************************************************************************
A ProMED-mail post
<http://www.promedmail.org>
ProMED-mail is a program of the
International Society for Infectious Diseases
<http://www.isid.org>

Date: Tue 21 Aug 2018
Source: Veterinary Practice News [edited]
<https://www.veterinarypracticenews.com/rocky-mountain-spotted-fever-epidemic-us-border-says-cdc-report/>


A study published by the Centers for Disease Control and Prevention
(CDC) says ticks are causing a deadly Rocky Mountain spotted fever
(RMSF) epidemic in Mexico, and health officials are concerned it could
spread to the US. Dr Luis Tinoco-Gracia, a research professor in the
School of Veterinary Medicine at Universidad Autónoma de Baja
California and director of the Laboratory of Veterinary Public Health
Sciences, in Mexicali, Mexico, and colleagues from the University of
California, Davis published the report in the September 2018 issue of
Emerging Infectious Diseases, the CDC's public health journal [1].

The RMSF epidemic began in 2008 in Mexicali, adjacent to the US border
in Baja California. In 2014, a fatal human case was reported in
Imperial County, California. In 2015, the Mexican Ministry of Health
declared an epidemiologic emergency, which as of 2018 has affected
approximately 4000 people. Since that time, 4 people who have been
carrying the disease and crossed the border to the US have died.

"Overall, since 2000, in the United States, the incidence of RMSF has
reportedly increased 4-fold; this dramatic increase may be caused in
part by increased transmission via the brown dog tick, but also by
changes in reporting and inclusion of false-positive test results in
case diagnoses."

RMSF, caused by _Rickettsia rickettsii_, is responsible for more human
deaths than any other tickborne disease in North America, according to
the authors, citing a total of 80 fatal cases reported from Sonora,
Mexico, during 1999 to 2007.

According to the authors, the brown dog tick (_Rhipicephalus
sanguineus_) has more recently emerged as a vector of _Rickettsia
rickettsii_, which increases the threat to humans because of _R.
sanguineus_' ability to adapt to indoor living.

The RMSF epidemic in Mexicali has not been contained and may be
spreading to other parts of Baja California and into the US, according
to the authors. "This large epidemic in a major city will require a
far greater and more creative public health response," the authors
continued. "Studying this epidemic offers an opportunity to understand
the origin and dynamics of this epidemic and can inform response to
emerging tickborne diseases in general."

[1. Tinoco-Gracia L, Lomelí M, Hori-Oshima S, et al. Molecular
confirmation of Rocky Mountain spotted fever epidemic agent in
Mexicali, Mexico. Emerg Infect Dis. 2018; 24(9): 1723-5;
<https://dx.doi.org/10.3201/eid2409.171523>.]

--
Communicated by:
ProMED-mail
<promed@promedmail.org>

[The journal article referenced in the news report above is extracted
below (<https://wwwnc.cdc.gov/eid/article/24/9/17-1523_article>):

Abstract
--------
"Since 2008, a large epidemic of Rocky Mountain spotted fever has been
emerging among humans and dogs in Mexicali, adjacent to the United
States in Baja California, Mexico. We molecularly confirmed the
causative agent; this information can be used to study the origin and
dynamics of the epidemic.

"Rocky Mountain spotted fever (RMSF), caused by the bacteria
_Rickettsia rickettsii_, is responsible for more human deaths than any
other tickborne disease in North America (1). During 1999-2007, a
total of 80 fatal cases were reported from Sonora, Mexico, alone (2).
Recent epidemics in Arizona (USA) and Sonora have been associated with
the brown dog tick (_Rhipicephalus sanguineus_) (3,4), whereas most
cases in the United States have been transmitted by bites of infected
_Dermacentor_ spp. ticks (5). The risk to humans is heightened by the
epidemiologic cycle of the brown dog tick, a cosmopolitan tick that
prefers the dog as its host and can live its entire life cycle in a
periurban setting, often spending its off-host time indoors. _R.
sanguineus_ ticks, in addition to being vectors of _R. rickettsii_,
are probable or confirmed vectors of _Leishmania_, _Coxiella
burnetii_, and _R. conorii_ (6).

"The study
----------
"In 2008, an epidemic of RMSF began in Mexicali, adjacent to the US
border in Baja California, Mexico. In 2015, the Mexican Ministry of
Health declared the epidemic an epidemiologic emergency, which as of
2018 has affected [about] 4,000 persons. In 2014, a fatal human case
in Imperial County, CA, USA, was probably associated with the Mexicali
epidemic. Overall, since 2000, in the United States, the incidence of
RMSF has reportedly increased about 4-fold (7); this dramatic increase
may be caused in part by increased transmission via the brown dog tick
but also by changes in reporting and inclusion of false-positive test
results in case diagnoses.

"Local response to the ongoing epidemic in Mexicali has involved the
Secretariat of Health and doctors and researchers at the Universidad
Autónoma de Baja California schools of medicine and veterinary
medicine. During 2008-2009, in the impoverished neighborhood of Los
Santorales in Mexicali, at least 13 persons died of RMSF. Under
agreement with the Sector Salud de Mexicali, the Universidad Autónoma
de Baja California veterinary team documented 81% seroprevalence among
local dogs and confirmed active _R. rickettsii_ infection in a human
resident by conducting PCR of kidney tissue (8). Of 120 persons from
Mexicali with clinical signs compatible with RMSF, 30 were positive by
PCR for the gene gltA, according to an unpublished method (9). In
2014, the local team partnered with researchers at the University of
California, Davis (Davis, California, USA), to further molecularly
characterize the strains of _R. rickettsii_ and _R. sanguineus_ ticks
from Mexicali. We provide definitive molecular confirmation of the
identity of the disease agent causing the Mexicali epidemic.

"The University of California, Davis, laboratory received DNA
extracted by use of QIAGEN Blood and Tissue Kits (Valencia, CA, USA)
from 16 cases from Mexico. Initial _R. rickettsia_-specific real-time
PCR for the citrate synthase gene (10) was positive for 10 samples. To
obtain products for DNA sequencing, we performed traditional PCR for
the ompA and 17kDa genes as published (11,12).

[...]

"We successfully obtained ompA and 17kDa products from 5 samples and
compared the sequences with those in the GenBank database by using
BLAST (<http://blast.ncbi.nlm.nih.gov/Blast.cgi>). For ompA, the
resulting 472-bp amplicons from the 5 products from Mexicali were 100
percent similar. For this gene, numerous accessions in GenBank also
have 100 percent homology with 100 percent coverage, including strains
Sheila Smith, Hauke, Hilo, Colombia, and Arizona. Sequences of 17kDa
spanned 206 bps and were also completely homologous among them. This
gene did not differentiate to species but was 100 percent homologous
with _R. rickettsii_, _R. parkeri_, and others in the database.
Representative sequences from Mexicali were submitted to GenBank
(accession nos. KY689935 for ompA and KY824575 for 17kDa).

"Among sequence-confirmed samples, data were not available for 1
sample. The other 4 samples were collected in June, July, and
September 2013 and April 2014. 2 samples were from men (41 and 25
years of age) and 2 from women (18 and 29 years of age); all patients
had dogs with ticks. Signs and symptoms were fever and headache for
all; for 1 patient, a rash and convulsions also developed. The 2 men
died and the 2 women survived with treatment. All patients had home
addresses in various parts of Mexicali, including central west,
southwest, and southeast bordering agricultural land. Clinical data
were not available for patients for whom samples were considered PCR
positive but not sequence confirmed, although inclusion of such
clinical data and risk factors could bias interpretation if they were
false positive or only weakly positive.

"Conclusions
------------
"The RMSF epidemic in Mexicali has not been contained and may be
spreading to other parts of Baja California and into the United
States. More data are needed before we can understand why this
epidemic emerged, where the specific areas of high risk for exposure
to infected ticks are located, and whether the particular _R.
rickettsii_ strain or relationship with this _R. sanguineus_ tick
strain is likely to be particularly invasive or virulent. Pockets of
RMSF have occurred in Mexico since at least 1947, when cases
attributable to the brown dog tick in Sonora, Sinaloa, Coahuila, and
Durango were described (13). Given the very limited phylogeographic
resolution available for _R. rickettsii_ in many of the commonly used
PCR products (14), it is not known whether the bacteria in the
Mexicali epidemic originated from Sonora or more distantly. Next steps
include obtaining a culture of the bacteria from Mexicali, studying
bacterial virulence in vitro or in animal models, and assessing vector
competence of the Mexicali _R. sanguineus_ tick strain for _R.
rickettsii_. Epidemiologic data on the spatial distribution and
prevalence of infection in dogs are needed.

"Aggressive intervention achieved partial and temporary resolution of
the Arizona and Sonora epidemics, which were localized and relatively
small; these interventions included dog spay and neuter programs,
treatment of houses against ticks, and use of a long-acting tick
collar (Seresto; Bayer, Shawnee Mission, KS, USA) directly on the dogs
(15). However, the dog collars were initially donated and are
prohibitively expensive and not feasible for the scope of the Mexicali
epidemic. This large epidemic in a major city will require a far
greater and more creative public health response. Studying this
epidemic offers an opportunity to understand the origin and dynamics
of this epidemic and can inform response to emerging tickborne
diseases in general."

The full journal article, including the references, is available at
the source URL.

Rocky Mountain spotted fever (RMSF) is a tickborne rickettsiosis,
caused by _Rickettsia rickettsii_. RMSF is distributed through much of
the USA, parts of southern Canada, and Central and South America.

The following is extracted from my moderator comments in a prior
ProMED-mail post Rocky Mountain spotted fever - Mexico: (SO, BN)
fatal, susp, RFI http://promedmail.org/post/20130831.1915146:

"The primary ticks that transmit _R. rickettsii_ in the United States
include the American dog tick (_Dermacentor variabilis_), Rocky
Mountain wood tick (_D. andersoni_), and brown dog tick
(_Rhipicephalus sanguineus_) (<http://www.cdc.gov/rmsf/>). A female
_D. variabilis_ (the American dog tick) can be seen at
<http://www.cdc.gov/mmwr/preview/mmwrhtml/rr5504a1.htm#fig1>. _R.
rickettsii_ is passed transovarially from adult females to their
progeny
(<http://www.sciencedirect.com/science/article/pii/0014489463900195>).

"In 2003, investigators in Mexicali, Mexico were reported to have
conducted an entomologic survey to determine the prevalence of the
brown dog tick _R. sanguineus_ among 94 stray and privately owned dogs
in the city and determined that 60 per cent of these animals were
infested with _R. sanguineus_, a prevalence far greater than reported
in other areas of Mexico and other parts of the world (Paddock CD,
Telford SR III. Through a glass, darkly: The global incidence of
tick-borne diseases. Available at:
<https://www.ncbi.nlm.nih.gov/books/NBK57015/>

"Subsequently, a large urban outbreak of RMSF that involved over 1000
cases occurred in Mexicali, Mexico in 2009. The Mexicali outbreak was
linked to transmission by the brown dog tick, and spread through
infected ticks by stray and free-roaming dogs. In 2009, surveys for
_R. sanguineus_ identified these ticks in all 14 districts of
Mexicali, where 96 per cent of the cases occurred
(<https://www.ncbi.nlm.nih.gov/books/NBK57015/>).

"RMSF has also been reported along the US side of the border. During
2010, Arizona reported 41 cases associated with tribal lands,
transmitted by the brown dog tick _R. sanguineus_ and also involved
roaming dogs and heavy infestations of brown dog ticks that resulted
in peri-domestic transmission and clustering of cases (Buelow ML. The
epidemiology of rickettsial diseases on the US Mexico border: An
analysis of incidence rates, clinical presentation and risk factors
associated with _Rickettsia rickettsii_, _Rickettsia typhi_, and
_Ehrlichia chaffeensis_ infection. Available at:
<https://legacy-etd.library.emory.edu/view/record/pid/emory:92fnd>

"The Mexican _R. rickettsii_ have been reported to differ genetically
from isolates in other endemic regions of northern, central, and
southern Americas; _Rhipicephalus_ ticks in Mexicali are also said to
differ genetically from _R. sanguineus_ found in the United States
(Eremeeva ME, Zambrano ML, Anaya L, et al. _Rickettsia rickettsii_ in
_Rhipicephalus_ ticks, Mexicali, Mexico. J Med Entomol. 2011; 48(2):
418-21; abstract available at
<https://academic.oup.com/jme/article-abstract/48/2/418/894598>).

"Mexicali, with a population of 689 775 in 2010, is capital of the
Mexican state of Baja California
(<http://en.wikipedia.org/wiki/Mexicali>). The city of Mexicali is
located in the Mexicali Valley on the US-Mexico border adjacent to its
sister city Calexico, California, which is located in the adjacent
Imperial Valley of California, south of the Salton Sea; a map of this
area can be found at
<https://www.google.com/maps/place/Mexicali,+Baja+California,+Mexico>.
Mexicali is an important industrial, as well as agricultural, center.
- Mod.ML

HealthMap/ProMED-mail map of Mexico:
<http://healthmap.org/promed/p/4138>]

[See Also:
2017
----
Rocky Mountain spotted fever - Mexico: (BC) fatalities
http://promedmail.org/post/20170525.5061586
Rocky Mountain spotted fever - Mexico: (CH) fatalities
http://promedmail.org/post/20170430.5004696
2014
----
Rocky Mountain spotted fever - Mexico (02): (BN)
http://promedmail.org/post/20140629.2572528
Rocky Mountain spotted fever - Mexico: (CA)
http://promedmail.org/post/20140510.2461790
2013
----
Rocky Mountain spotted fever - Mexico: (SO, BN) fatal, susp, RFI
http://promedmail.org/post/20130831.1915146
2012
----
Rocky Mountain spotted fever - Mexico (02): (CA)
http://promedmail.org/post/20121114.1409214
Rocky Mountain spotted fever - Mexico: (BN)
http://promedmail.org/post/20120828.1268087]
.................................................sb/ml/mj/lxl
*##########################################################*
************************************************************
ProMED-mail makes every effort to verify the reports that
are posted, but the accuracy and completeness of the
information, and of any statements or opinions based
thereon, are not guaranteed. The reader assumes all risks in
using information posted or archived by ProMED-mail. ISID
and its associated service providers shall not be held
responsible for errors or omissions or held liable for any
damages incurred as a result of use or reliance upon posted
or archived material.
************************************************************
Donate to ProMED-mail. Details available at:
<http://www.isid.org/donate/>
************************************************************
Visit ProMED-mail's web site at <http://www.promedmail.org>.
Send all items for posting to: promed@promedmail.org (NOT to
an individual moderator). If you do not give your full name
name and affiliation, it may not be posted. You may unsub-
scribe at <http://ww4.isid.org/promedmail/subscribe.php>.
For assistance from a human being, send mail to:
<postmaster@promedmail.org>.
############################################################
############################################################

List-Unsubscribe: http://ww4.isid.org/promedmail/subscribe.php

0 comments:

Post a Comment