the study was conducted in 100 households of 9 affected villages of engil district on the edge of herat city . households were included if they were located on 3 randomly selected transect lines and if members of the households owned either cattle or sheep . because there are no reliable estimates on seroprevalence of cchf in afghanistan , we estimated prevalence of immunoglobulin ( ig ) g to be 7% ( 2,3 ) . a sample size of 160 persons was required to detect this prevalence at the 95% confidence level . allowing for cluster sampling at the household level , 320 persons was the target sample size ( 90 households , assuming an average of 3.5 persons > 15 years of age per household ) . from each household , all members > 15 years were surveyed , if they gave consent . sheep and cattle were selected as livestock types , and 1 or 2 animals per household were randomly selected . inclusion criteria for humans were residing in a livestock - owning household , giving informed consent , being > 15 years of age , willing to answer the risk factor questionnaire , and willing to give 5 ml of blood . for collection of blood samples and vector specimens from sheep and cattle , permission was given by the head of household . a standardized , structured , and pretested questionnaire that covered individual data for each participant , including personal details , exposure variables , and self - reported disease history , was used . animal data were collected from each household and included each animal s origin , tick exposure , age , and sex . blood samples from human participants were collected by trained health workers according to standard procedures . blood samples were centrifuged at room temperature at the local laboratory on the day of collection . serum was separated , frozen , and transported to kabul for storage and onward shipment . a sandwich / indirect elisa detected specific igg at a 1:100 dilution for all human samples by using the vector - best diagnostic kit , ( vector - best , novosibirsk , russia ) . we have previously compared this kit with an in - house elisa ( us army medical research institute for infectious diseases , fort detrick , md , usa ) , and the results were comparable in all samples tested ( l. mustafa et al . , unpub . we used an in - house elisa using the ibar 10200 strain of cchf as antigen ( us army medical research institute for infectious diseases ) and anti - species igg horseradish peroxidase  conjugated ( kpl inc . , gaithersburg , md , usa ) to test for igg in all animal serum specimens . data were analyzed by using stata version 8 ( statacorp , college station , tx , usa ) . the primary outcome was seropositivity among household members , with secondary outcomes being seropositivity in animals and the presence of virus in ticks . exposure factors for seroprevalence were identified on an a priori basis and appropriate measures of statistical significance were applied to detect differences at the 95% confidence level . the study was approved by the ethics boards of namru-3 and the afghan public health institute , afghanistan . in total igg seroprevalence was 37/330 ( 11.2% , 95% confidence interval [ ci ] 8.015.1 ) . of all the potential explanatory variables , only 2 factors were associated with an elevated risk of igg positivity : daily contact with cattle ( 33/264 [ 12.5% ] vs. 1/52 [ 1.8% ] ;  = 5.1 , p = 0.02 ) and exposure to raw animal skins ( 24/144 [ 16.7% ] vs. 12/176 [ 6.8% ] ;  = 7.7 , p = 0.006 ) . self reported clinical illness ( fever ) occurred in 55% of participants over a 5-month reporting period . among the participants , 20.8% reported that they had had an illness involving bleeding from teeth , gums , and or other parts of the body , but this event was not associated with igg positivity or with age group . these results suggest that the risk for cchf exposure is uniformly high among the population . the oldest age group shows an approximate lifetime risk for exposure and seroconversion of 17% ( 95% ci 10.2%25.8% ) . ninety - two cattle and 40 sheep were included , and serologic analysis of their blood samples was conducted . seroprevalence was 79.1% ( 95% ci 69.0%87.1% ) among cattle and 75.0% ( 95% ci 57.0%88.5% ) among sheep . prevalence was uniformly high regardless of age , sex , or origin of the animals , suggesting that the disease is highly endemic in the livestock population . among our sample , ticks ( n = 259 ) from domestic animals were predominantly adult hyalomma marginatum ( 94.6% ) . engorged females were found more on cattle than on sheep ( 43% and 27% , respectively ) . seroprevalence in this population of animal owners is higher than in other reported studies from the region ( 3,4 ) , and the risk for exposure appears approximately uniform . the route of transmission to humans is either through the bite of ticks or through contact with infected animals or animal products . this second route of transmission is probably more important in iran and afghanistan than tick - borne transmission . control of cchf requires control of the disease vector , and surveillance is necessary to ensure optimum timing of interventions such as livestock dipping or sponging because tick abundance is highly seasonal . further research on rates of antibody acquisition among humans and animals , virus transmission dynamics , and effectiveness of disease control measures is required . cchf is a regional public health concern of larger than previously acknowledged significance and requires control mechanisms from both the health and agriculture sectors .
in response to an outbreak of crimean - congo hemorrhagic fever in western afghanistan , we measured immunoglobulin g seroprevalence among household members and their animals . seroprevalence was 11.2% and 75.0% in humans ( n = 330 ) and livestock ( n = 132 ) , respectively . 
 persons with frequent exposure to cattle had an elevated risk of being immunoglobulin g positive .