during august 2010december 2012 , we recruited all patients who had clinically suspected m. ulcerans infection and had attended a clinic in the buruli ulcer  endemic asante akim north district in ghana .
age- and sex - matched household contacts of patients were also asked to participate ; all study participants were > 5 years of age .
the study protocol was approved by the ethics review committee of the school of medical sciences , kwame nkrumah university of science and technology ( chrpe/91/10 ) .
whole blood samples were taken at baseline , at week 6 , and at week 12 from 66 patients in whom the diagnosis of buruli ulcer disease had been confirmed by pcr for the is2404 repeat sequence specific for m. ulcerans ( 8) ; samples were also obtained from 20 household contacts at the same intervals .
the samples were heparinized , and peripheral blood mononuclear cells were separated from 10-ml samples .
filarial infection was confirmed on a blood film stained with giemsa and delafield hematoxylin and examined for microfilariae at 10 and 40 magnification ( the knott technique ; 10 ) .
m. perstans nematodes were distinguished from l. loa and w. bancrofti nematodes by their small size and the absence of a sheath ( figure 1 ) .  
m. perstans nematodes can be distinguished from loa loa and wuchereria bancrofti nematodes by relative small size , detection in blood samples obtained during the day , and lack of a sheath .  
patients in whom m. ulcerans infection was found were treated with 10 mg / kg oral rifampin and 15 mg / kg intramuscular streptomycin , administered daily at village health posts under direct observation for 8 weeks ( rs8 treatment ) .
the patients were followed up every 2 weeks in the clinic and monitored for complete healing or recurrence of skin lesions .
we compared the proportion of household controls versus the proportion of buruli ulcer patients infected with m. perstans nematodes and the time to complete healing of m. ulcerans lesions in co - infected versus monoinfected patients .
categorical variables such as sex , clinical form of m. ulcerans lesion , and category of m. ulcerans lesion were compared by using the fisher exact test , and cumulative healing was compared by using the log - rank test .
we found all forms of m. ulcerans disease among the group of patients ; proportions of each type and category are shown in the table .
of 66 patients with m. ulcerans disease , 15 ( 22.7% ) were co - infected with m. perstans nematodes , whereas 4 ( 13% ) of 30 household controls had m. perstans infection ( p = 0.4 by fisher exact test ) .
three patients in the co - infected group and none in the m. ulcerans  monoinfected group reported pruritus .
no other clinical signs of m. perstans infection were found . * na , not applicable . 
comparison of combined m. ulcerans monoinfected and m. ulcerans co - infected with m. perstans versus household contacts , determined by 2-tailed fisher exact test . 
comparison of m. ulcerans co - infected with m. perstans versus m. ulcerans monoinfected group , determined by 2-tailed fisher exact test . all 66 patients completed rs8 treatment , but 9 were lost to follow - up during the 12-month follow - up period .
buruli ulcer lesions healed completely in 14 co - infected patients by 58 weeks ( median 20 weeks , 95% ci 14.630.2 ) and in 43 monoinfected patients by 50 weeks ( median 21 weeks , 95% ci 16.725.5 ) .
we found no difference in cumulative time to healing for co - infected versus monoinfected patients ( p>0.05 by log - rank test ) ( figure 2 ) .
buruli ulcer patients who had m. perstans nematodes co - infection were treated with doxycycline ( 200 mg ) and ivermectin ( 150 g / kg ) daily for 6 weeks , starting during the second to fourth week of rs8 treatment .
viable microfilariae were still visible in peripheral blood mononuclear cell cultures from all co - infected patients after ivermectin and doxycycline treatment , but pruritus subsided in the 3 patients who had reported it .
survival analysis curve of cumulative healing for patients with mycobacterium ulcerans infection who were co - infected with mansonella perstans nematodes compared with those who had m. ulcerans monoinfection , ghana , august 2010december 2012 .
no difference in cumulative healing was found between the 2 groups ( p = 0.93 by log - rank test ) .
we found co - infection with m. perstans in 23% of buruli ulcer patients in a disease - endemic district in ghana , but this prevalence was not significantly difference from prevalence among household contacts who served as controls ( 13% ) .
as with buruli ulcer , m. perstans filariasis is predominantly found in rural populations and infection begins in childhood ; the highest infection rates are found in children 1014 years of age ( 11 ) , similar to those for children at highest risk for m. ulcerans infection .
m. perstans infection occurs in ghana and was seen in the volta region of ghana around hohoe during the 1990s , but its prevalence is unknown ( 12 ) , and no information is available about the average number of worms per infection . in uganda ,
prevalence of m. perstans infection has been found to range from 0.4% to 50% ( 13 ) .  
m. perstans nematodes are transmitted by the bites of culicoides midges , but it is not known whether m. perstans  infected midges can be co - infected with m. ulcerans . in a guinea pig model , skin penetration was shown to be a requirement for establishment of m. ulcerans disease ( 14 ) , and it has been postulated that mosquito bites cause m. ulcerans disease in australia ( 6 ) . these organisms might share a common route of transmission , but our findings in this small study do not support this concept .  
our findings suggest that m. perstans nematodes are common in rural ghana and coincidentally infect patients with m. ulcerans disease , necessitating the consideration of these organisms in the management plan of buruli ulcer patients .
although often asymptomatic , m. perstans infection may cause eosinophilia , subcutaneous swellings , aches , pains , and skin rashes in a considerable proportion of patients ( 9 ) .
because filarial nematodes are known to polarize the host immune responses from t - helper type 1 cells needed for protection against mycobacterial infections , toward humoral and t helper type-2 mediated immunity , we plan to undertake a study to investigate this interaction .
 during august 2010december 2012 , we conducted a study of patients in ghana who had buruli ulcer , caused by mycobacterium ulcerans , and found that 23% were co - infected with mansonella perstans nematodes ; 13% of controls also had m. perstans infection . 
 m. perstans co - infection should be considered in the diagnosis and treatment of buruli ulcer . 