| Objective,Scrub typhus is a zoonosis caused by Orientia tsutsugamushi which is transmitted by chigger mites.At present,the endemic regions of scrub typhus tends to move northward in China.In this process,the epidemic characteristics,vectors,reservoirs and genotypes of scrub typhus have changed compared with the southern provinces.The first outbreak of scrub typhus in Fuyang City,Anhui Province,was last sustained from September to November 2008.Afterwards,there had been an outbreak of unknown fever causes from September to November every year,which was clinically diagnosed as scrub typhus.The number of cases has been increasing every year,endangering human health seriously;nevertheless,the epidemic characteristics and genotype of scrub typhus are still unclear.This study makes a series of researches on these problems.Methods We carried out the pathogen study of epidemic diseases on the blood samples of clinical patients,including the isolation and culture of Orientia tsutsugamushi,nucleic acid detection and antibody detection of two pairs of serum ascariasis,then further verified their genotypes;582 rodents and 1784 chigger mites were conducted for the host and vector research;epidemiological analysis of 4547 cases of clinical diagnosis scrub typhus in Fuyang City from 2008 to 2015 was inverstigated;combined with agricultural data,188 patient questionnaires learn to determine the risk factors for the development of tsutsugamushi disease.Results The pathogen of Orientia tsutsugamushi was isolated with Kawasaki type as the main genotype.The original study indicated that patients in Funyang City had 36.43%(204/560)positive rate of blood nucleic acid detection,and 74.40%(125/168)specimens of IgG detection increased or decreased in four or more times.Epidemiological studies have found that scrub typhus is distributed in every county under the jurisdiction of Fuyang City(x~2=659,P<0.05).For occupational characteristics,farmers were the high-risk group(x~2=52.568,P<0.05).The incidence was higher in females than in males(x~2=46.588,P<0.05).The high risk age was from 60to 69.For risk factor analysis,a total of 6,690 traps or cages were used in spring and autumn to capture 582 rodents during the period of 2008-2015.The t-test confirmed that the rodent density in autumn in Fuyang City was higher than in spring,which from April to June was 1.03%,1.50%and 2.16%,and from September to December was7.89%,14.43%,9.57%and 3.04%.A total of 1784 chigger mites were collected from rodent ears,of which 87.05%(1553/1784)were Leptotrombidium scutellare chigger mites.The Leptotrombidium deliense was 72.85%(424/582)of all the captured rodents and infection rate was 41.98%,0,0,9.52%from April to June,19.12%,52.84%,55.36%,30.77%from September to December.From April to June,The chigger mite infestation rate(Ir)and the infested indices by chigger mites(Ii)were 25%,0.125,23.08%,0.154,23.81%,0.667,54.41%,2.029,73.30%,4.199,60.71%,5.688,26.92%,and 0.815,respectively.Orientia infection chigger mites from September to December,respectively 16.22%,45.47%,44.12%and 28.57%,the rest of the month Leptotrombidium scutellare chigger mites do not carry pathogens.The trend of the density,Ir and Ii of Apodemus agrarius was the same as the number of Orientia tsutsugamushi infection.The incubation period of 188 patients with scrub typhus was7.11±3.24 days.According to the epidemiological analysis of 188 questionnaire,the earliest case occurred on September 11,and the number of cases in September was very small(please indicate how small it is).The number of cases increased in October,basically reached a peak in early November,and then decreased,and a few cases were seen occasionally in December.According to the statistics of living environment,157among 188 patients lived near the tenable or trench,and there were rat holes and rats frequently emerged in their homes.Correlation analysis indicated that there was a positive correlation between the cultivated area of autumn crops and the occurrence of scrub typhus(r=0.856,P<0.05).In Fuyang City,the main crops in autumn were corn,soybean,sweet potato and a small amount of rice.Both sweet potato field and soybean field were harvested manually,corn field was harvested semi mechanically,and rice field was harvested by mechanization.Linear regression showed that the main way for patients to contract scrub typhus was manual harvesting.Before the onset of disease,185among 188 patients had a field work history,mainly working in corn field,soybean field and sweet potato field,a total of 183 people(97.34%),and 141 people(76.22%)were infected by artificial harvesting of soybean and sweet potato.Discussion The clinical diagnosis of the fever of unknown origin in autumn and winter in Fuyang City was scrub typhus.The laboratory diagnosis has confirmed the tsutsugamushi disease.The popular genotype of Orientia tsutsugamushi in Fuyang City is mainly Kawasaki type.The epidemiological characteristics of the incidence of scrub typhus in autumn and winter in Fuyang City were described in details for the first time.It proves that scrub typhus is widely epidemics in Fuyang City,and it is outbreak in autumn.The peak incidence is from October to November.Farmers are at high risk,with a high incidence of 60~69 years old,and the incidence of women is higher than men.Combined with the investigation of the incubation period of tsutsugamushi disease,the risk factors of scrub typhus were analyzed for the first time.It is considered that the annual rodent survey in September is of great significance.It is proposed that the density of Apodemus agrarius in autumn is higher than or equal to 7.89%,and the rate of banding is higher than or equal to 54.41%.The infested indices by chigger mites is higher than or equal to 2.029,the infection rate of Apodemus agrarius reaches 19.12%,and the positive rate of the Orientia tsutsugamushi of Leptotrombidium scutellare reaches 16.22%,which is an early warning indicator for the outbreak of scrub typhus;Analysis shows that living near the tanabe or trench,because of increased opportunities to contact with rodents,the chance of infection with Orientia tsutsugamushi has also increased,and artificial harvesting has increased the chance of contracting Orientia tsutsugamushi.Pathogenic research has been guiding significance for clinical diagnosis and treatment,and helps to reduce the misdiagnosis rate and missed diagnosis rate of scrub typhus.The scientific data of epidemiological investigation and risk factor analysis provides the scientific and theoretical basis for the prevention and control of autumn-winter type scrub typhus in the plain north of the Yangtze River in China. |
PDF Full Text Request