leprosy is the clinical manifestation of infection with mycobacterium leprae .  with a slow growth rate of division every 12 - 13 days at an optimum temperature of 30c , m. leprae bacteria infect macrophages and schwann cells . infection of schwann cells predisposes infected individuals to nerve damage , rendering leprosy , a chronic disabling infection with insidious onset typically characterized by the early involvement of skin and peripheral nerves the response can limit bacterial growth and dissemination , resulting in few localized skin lesions and the definition of such patients as paucibacillary ( pb ) . in cases where the response does not control bacterial growth , high bacterial burden arises , infection becomes systemic and many disseminated lesions and significant nerve function impairment can be observed ; these patients are defined as multibacillary ( mb ) . although early detection is recommended by world health organisation ( who ) , diagnosis is currently achieved only upon the recognition of clinical symptoms by skilled clinicians . as leprosy is usually associated with low socioeconomic development , patients often have limited access to medical care and evade early detection . estimates are that patients are misdiagnosed an average of 2 times , resulting in a substantial amount of time passing from the onset of clinical signs to proper diagnosis and treatment [ 47 ] . these issues can have a devastating impact on the patient , as the longer a patient goes untreated the greater their chance of developing irreversible nerve damage [ 810 ] . in addition , untreated mb leprosy patients are likely transmitting m. leprae and inadvertently generating new cases . labor - intensive physical examination for skin and peripheral nerve involvement can be conducted at regular intervals ( typically every few months and/or at annually ) in recognized leprosy - endemic regions to detect suspected cases before advanced clinical symptoms and disabilities are established . while new cases do still arise from the general population , surveillance campaigns are often streamlined by focusing screening for possible preclinical infections in household contacts of diagnosed cases , as these individual , are at an elevated risk of developing leprosy [ 1113 ] . the application of specific , simplified diagnostic methods within surveillance campaigns could expand the number of individuals analyzed or increase the frequency of analyses . for example , quantitative measurement of antibodies against the phenolic glycolipid ( pgl)-i and leprosy idri diagnostic-(lid- ) 1 antigens has previously been instructive for diagnosis of mb leprosy [ 1416 ] . more importantly , antibody levels against either of these antigens have previously been reported to rise prior to the attainment of clinical diagnosis [ 16 , 17 ] . despite the pronouncement of the elimination of leprosy at a national level at the 15th international leprosy conference , beijing 1998 , leprosy remains prevalent in some of the difficult - to - access mountain regions of south west china [ 18 , 19 ] . although labor - intensive and logistically complicated , clinical surveillance teams visit residents in several of these regions on a regular basis . this program facilitates the relatively early recognition of patients and the prompt provision of multidrug therapy ( mdt ) . in this study , we applied simple elisa to sera collected from suspected leprosy cases in honghe prefecture , yunnan province , to quantify antibodies against the pgl - i and lid-1 antigens and evaluate the utility of these within active surveillance programs for leprosy . sera were obtained from patients with leprosy ( mb and pb ) or pulmonary tuberculosis ( tb ) and healthy household contacts ( hhcs ) of mb leprosy patients within a hyperendemic site in south west china . mb and pb leprosy patient sera used in this study were derived from recently diagnosed , previously untreated individuals ( table 1 ) . sera from healthy individuals residing in a leprosy nonendemic region served as additional controls ( nc ) . within an active surveillance program , hhcs of 9 mb and 1 pb patients from a leprosy - endemic village ( coded as a3 - 1 * ) were first assessed for leprosy by physical examination in early 2008 . additional samples were collected during a follow - up trip in february 2009 and when leprosy onset was suspected ( i.e. , the appearance of suspicious lesions and/or rising antibody responses ) . a third visit to reexamine the hhc antibody responses were assessed by elisa using the well - known glycolipid ( nd - o - bsa ) and the specific protein antigen ( lid-1 ) [ 1416 ] . polysorp 96 well plates ( nunc , rochester , ny ) were coated with 1  g / ml recombinant protein or 200  ng / ml nd - o - bsa , the synthetically derived b - cell epitope of pgl - i conjugated to bsa , in bicarbonate buffer overnight at 4c and blocked for 1  hr at room temperature with pbst with 1% bsa on a plate shaker . plates were washed with buffer only , and horseradish peroxidase - conjugated igg or igm ( rockland immunochemicals , gilbertsville , pa ) , diluted in 0.1% bsa , was added to each well and incubated at room temperature for 1  hr with shaking . after washing , plates were developed with peroxidase color substrate ( kirkegaard and perry laboratories , gaithersburg , md ) , and the reaction was quenched by the addition of 1  n h2so4 . elisa was conducted against the nd - o - bsa and lid-1 antigens that have previously demonstrated the potential to diagnose ( or confirm diagnosis of ) leprosy . as previously reported , when compared with nondiseased individuals , mb patients had highly significantly elevated antibody titers against both nd - o - bsa and lid-1 ( figure 1 and table 1 ) . although pb patients as a group could not be discriminated from the various control groups incorporated in the study ( hhc , tb , and nc ) , a subset of pb patients did display elevated antibody titers ( figure 1 ) . sera collected during scheduled visits of leprosy patient households by the surveillance team were analyzed by elisa . the rising antibody responses in the successive sera obtained from hhc - c13 indicated a potential onset of leprosy , alerting the monitoring team to return and examine this contact . during a physical checkup by the surveillance team , hhc - c13 appeared with numerous oval - shaped punched out lesions , with diminished sensation , of varying size in both the abdomen and the back ( figure 2 ) . upon histological examination of a biopsy collected from the edge of a back lesion , epidermal atrophy , vascular dilation , and lymphocytic infiltration could be observed in the neurovascular bundle ( figure 3(a ) ) , and perineural and perivascular infiltration could be observed in the dermal nerve ( figure 3(b ) ) . as expected , acid fast bacilli ( afb ) were numerous , and the patient was determined to have a 3 + bacterial index ( figure 3(c ) ) . two serum samples had already been obtained from this individual , and a third sample was collected at the time of clinical diagnosis of leprosy . analysis of these sera revealed that igm levels against nd - o - bsa rose between the second and third collections ( table 2 ) . even more strikingly , igg levels against lid-1 were found to have risen between each collection . the most likely source of m. leprae infection in this patient was her grandfather , who was a confirmed mb leprosy case with whom she shared a residence . it is noteworthy that he died in 2006 , suggesting that this infection had been propagating for a minimum of 3 years . although the laboratory data mitigated a clinical examination that led to the diagnosis of mb leprosy and provision of treatment , our data indicate that in this particular case , diagnosis based upon this antibody response could have been made , at a minimum , 8 months earlier than that achieved by clinical examination and before the appearance of such distinct symptoms . regular clinical examinations of contacts of known leprosy cases are an effective , albeit labor - intensive , method of detecting new cases . our data indicates that this process could be streamlined , and even expanded , by the use of serologic assays to screen this population . we suggest that rising antibody titers could be used as a trigger of fulminant physical examination or increased monitoring of particular individuals .
leprosy is a disabling chronic infection , with insidious onset that often evades early detection . in order to detect new leprosy cases in a timely manner , we conducted surveillance visits in some difficult - to - reach mountain areas in south west china where the disease is still prevalent . 
 our data confirm that chinese multibacillary ( mb ) leprosy patients have strong antibody responses against mycobacterium leprae antigens nd - o - bsa and lid-1 . 
 contacts of clinically diagnosed patients were then monitored at regular intervals by both physical examinations and the laboratory determination of antibody responses in sera collected during these examinations . 
 elevations in antibody titers indicated the onset of mb leprosy in one of the contacts , and diagnosis was subsequently confirmed on physical examination . 
 our data indicate that rising antibody titers can be used as a trigger for physical examination or increased monitoring of particular individuals in order to provide early leprosy diagnosis .