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Letter
Typhus Group Rickettsiae Antibodies
in Rural Mexico
Virginia E. Alcantara,* Esperanza G. Gallardo,† Chao Hong,* and David
H. Walker*
*WHO Collaborating Center for Tropical Diseases, University of Texas Medical
Branch, Galveston Texas, USA; and †Instituto de Salud del Estado de Mexico,
Toluca, Mexico
Suggested citation
for this article:
Alcantara VE, Gallardo EG, Hong C, Walker DH. Typhus group rickettsiae
antibodies in rural Mexico. Emerg Infect Dis [serial online] 2004 Mar
[date cited]. Available from: http://www.cdc.gov/ncidod/EID/vol10no3/03-0438.htm
To the Editor: In 2002, the risk of transmission of epidemic typhus
in the state of Mexico was assessed by analyzing serum specimens from
393 residents of previous typhogenic areas for immunoglobulin (Ig) G antibodies
against Rickettsia prowazekii. Louseborne typhus has been a historic
scourge in Mexico. In 1576, in a population of 9 million, 2 million deaths
were attributed to epidemic typhus (1). These illnesses
primarily affected indigenous peoples, who called the illness cocolixtle
and matlazahuatl (2).
In 1951 a national campaign against louseborne typhus was begun by using
newly developed technologic approaches, antibiotics, and insecticides,
resulting in decreases in the incidence and case-fatality rate. In 1951
>1,000 cases and 737 deaths caused by epidemic typhus were reported
in 18 states, and 6,781 localities were identified as at risk (3).
By 1965, only 36 cases and no deaths were reported from 12 states with
4,841 localities at risk. Most cases occurred during the cold months of
November–April. One third of cases occurred in persons 19–29 years of
age with nearly 40% of the deaths in patients aged 15–44 years. In 1979,
10 years had passed without any cases of epidemic typhus reported in Mexico.
In the 1980s, three outbreaks of typhus occurred in rural communities,
two in Chiapas and one in the state of Mexico (4).
In the state of Mexico, during the period 1893–1907, 7,353 epidemic typhus
deaths were reported (annual mortality rate, 52.4/100,000 population);
from 1939 to 1943, 1,220 cases were reported with 707 deaths (annual mortality
rate, 12.1/100,000 population); and from 1959 to 1963, 64 cases were reported
with 14 deaths (annual mortality rate, 0.1/100,000 population) (3).
In 1967, Atlacomulco, a county in the state of Mexico that had been free
of typhus for 5 years, experienced an outbreak of louseborne typhus associated
with a case of Brill-Zinsser disease in a 76-year-old man who had a history
of epidemic typhus. Forty cases were diagnosed and one death occurred
(3). The last outbreak in the state of Mexico occurred
in 1983 in San Juan Cote in San Felipe del Progreso County, with 22 ill
persons and one death (4). Since then, a public health
program against Pediculus humanus corporis has been conducted in
five counties with epidemiologic surveillance for cases of reactivation
of latent infection. At the beginning of the 1980s, the rate of infestation
with P. humanus corporis (mazahua) in the indigenous population
of the state of Mexico was 100%; in 1988, 58%; and in 1990, 15%. In 1999,
indices of infestation between 5% and 12% were detected in this population
(5).
In 2002, personnel from the office of the Secretary of Health of the
State of Mexico evaluated the risk to the population who lived in previously
typhogenic areas to measure the impact of their programs (5).
In a cross-sectional study, 393 human serum specimens were analyzed by
immunofluorescence assay (IFA) for IgG antibodies against R. prowazekii,
and a titer of 64 or higher was considered positive (6).
Antibodies against R. prowazekii were detected in 74 serum samples
(seropositivity, 18.8%; 26% for males and 18% for females). The prevalence
of antibodies to R. prowazekii increased with age; 1–14 years of
age (seropositivity 0%), 15–24 years (14%), 25–44 years (17%), 45–64 years
(24%), and >65 years (48%). Thirty-three (45%) of the serum
specimens had a titer of 64, 25 (34%) had a titer of 128, and 16 (22%)
had a higher titer. All eight serum specimens with a titer of >512
were from persons >45 years of age.
The high seroprevalence suggests that this population had extensive exposure
to the agent of typhus and its louse vector in the past. The finding of
two subjects aged >65 years with a titer of 1,024 and four subjects
aged >45 years with a titer of 512 suggests reactivation of
latent R. prowazekii with a resulting boost in their antibody titers.
These possible cases of Brill-Zinsser disease were likely not severely
ill and recovered either with antimicrobial treatment that was effective
against R. prowazekii or by immune control of the infection without
a specific diagnosis.
That IgG antibodies against R. prowazekii are absent in young
persons suggests that this rickettsia has not been circulating in this
population during recent years. The high seroprevalence suggests a human
reservoir of latent R. prowazekii in this population. The presence
of human body lice in this population indicates that there is risk of
spreading R. prowazekii from an index patient with Brill-Zinsser
disease to persons in contact with the patient.
Although the general lack of attention to R. prowazekii by scientists,
physicians, and public health agencies would lead one to believe that
typhus has been eliminated as a public health concern, the recent occurrence
of a large epidemic in Burundi (7), infected lice in
Rwanda, an outbreak in Russia, a documented case originating in Algeria,
and outbreaks every year in Andean Peru (8) indicate
that global attention should be directed to surveillance, risk assessment,
diagnostic capability, and planning for rapid epidemic control to avoid
establishing a large reservoir of latent infection for future epidemics
originating from recrudescent typhus in louse-infested populations. Typhus
likely poses a similar threat in other parts of the world including the
Himalayas, Andes, Afghanistan, and highlands of Africa. Even in industrialized
countries, the diagnosis of typhus is likely to be delayed or missed.
The potential threat of bioterrorist-disseminated, aerosol-transmitted
typhus emphasizes that enhanced attention to and knowledge of typhus are
needed throughout the world (9). The requirement concerns
not only physician awareness but also wide availability and application
of the most appropriate diagnostic laboratory methods.
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