Rabies is endemic and priority zoonotic disease in Nepal. The death of 200 [1], human being and 300 animals [2], per year has been reported in this country. The disease has been confirmed in cattle, buffaloes, goats, alpaca, dogs and mongoose [3]. Rabies occurs throughout the year and dog is the principle vector for the transmission of disease. Rabies Vaccine Laboratory in Kathmandu produces 50, 000 doses of cell culture vaccine for animal use whereas vaccine for human use is imported from other countries [3]. Health authority purchased 300,000 doses expending 1 million USD every year to purchase inactivated cell culture rabies vaccine for human use (personal contact with EDCD). In 2012, 334,737 doses of cell culture rabies vaccine were purchased by Epidemiology and Disease Control Division, the Department of Health Service. Vaccine is not available to all victims at risk in country side therefore the case fatality is higher [4]. More than 45,000 people receive post exposure vaccination annually in Nepal. Number of dog bitten cases per month coming to Sukraraj Tropical Hospital (STH) for post exposure treatment is 1520 and in average 50 cases receives post exposure rabies vaccine daily in this hospital (Personal contact with STH Hospital).

Human or animal health workers, in contact with rabid animal or patient or rabies virus are at high risk of rabies infection. Therefore pre exposure rabies vaccine has been recommended by World Health Organization (WHO) for medical peoples, veterinarian and laboratory personals. The immunization protocol includes three injections, e.g. at days 0, 7, and 28. The serological evaluation of immunization is made 1-3 weeks after the last injection, and checked every 6 months in the case of laboratory workers or every 2 years for other diagnosticians. Booster vaccination must be given when the titer falls below 0.5 International Units (IU) per ml. In the absence of serological monitoring, the vaccination regimen should consist of a booster vaccination at 1 year and thereafter every 1-3 years [5,6]. Therefore the antibodies tire in response of rabies vaccine in vaccinated people or animal should be tested periodically by performing Rabies Fluorescent Focus Inhibition Test (RFFIT) after vaccination to avoid unnecessary vaccination and to reduce the risk of rabies infection. In this study we have measured antibody tire against rabies vaccine in professional people who have high risk hazard of Rabies.

Blood samples were collected from 44 persons (13 female and 31 male) after getting oral consent in 2014. Sampled persons were 21 medical professional and 23 veterinary professional having occupational risk of rabies. Among medical professional 4 were doctors and 17 were technicians (paramedical) working at Sukraraj Tropical Hospital, Kathmandu. Among veterinary professional 9 working at Central Veterinary Hospital, 7 working at Central Veterinary Laboratory and 7 working at Rabies Vaccine Production Laboratory in Kathmandu. All 44 samples person were 28-58 years old. Among 44 collected samples, 4 were from unvaccinated persons and rest was from vaccinated persons in different time. Serum was separated labeled accordingly and stored at -20°C in refrigerator. The description of samples was presented in table 1. Samples were packed and transferred to Centre of Disease and Prevention Rabies Laboratory, Atlanta USA according to IATA instruction. The serum samples were subjected to RFFIT according to protocol described by World Health Organization (1996).

Table 1: Result of RFFIT of human serum samples collected from Nepal in 2014.

The test revealed that 15.9% of tested samples had antibody titer 0.043 IU/ml below than WHO recommendation 0.5 IU/ml serum and 84.1% of tested samples had adequate titer ranging from 1.1 to 3316 IU/ml. Out of 40 sample collected from vaccinated person 7.5% had low antibody titer. The result of RFFIT has been presented in table 1. The variation of antibody titer was directly related to the number or frequency of dose, type of vaccine and duration between vaccination time and time of sample collection. Six medical professional and one veterinary professional had low level of titer. The low level of titer in 4 unvaccinated medical professional was normal and expected in control samples. Sample No. 1 revealed low titer because sampled person had taken nerve tissue post exposure vaccine 15 years ago. Low antibody titer of sample No. 8 (medical professional) and sample No. 29 (veterinary professional) might be due to lack of booster dose both of them had taken pre-exposure vaccination 1-3 years ago. However other factor such as host ability to immune response, quality of vaccine and health status may influence the production of antibody titer in host [7]. Sample No. 7 had highest titer 3396 IU/ml because

Sampled person had taken pre exposure cell culture inactivated vaccine and again booster dose 3 month ago. All 40 vaccinated people had taken inactivated cell culture vaccine except sample No. 1 and all sampled person with adequate antibody titer had taken booster in addition to pre or post exposure vaccine. This study showed that 15.9% of sampled professional were working at risk at Sukraraj Tropical Hospital and Central Veterinary Hospital were rabid patient were examined and treated. Among 7, 5 were female and 2 were male by sex. Therefore pre exposure vaccination and periodic sero-monitoring of antibody titer and administration of booster for person working at risk is urgent which is lacking in Nepal. WHO and World Organization for Animal Health has also recommended such preventive measures to be adopted by people at risk of rabies who work in medical and veterinary hospital or laboratories [4,8].

All medical or veterinary professional who are at risk of rabies infection are recommended to take pre-exposure inactivated cell culture rabies vaccine. Antibody titer in vaccinated persons should be tested periodically to ensure the antibody level of protection and to inject booster dose of vaccine accordingly.

Authors would like to acknowledge Dr. Todd Smith and Dr. Ashutosh Wadhwa, CDC, Atlanta, USA for their technical support and help conducting RFFIT test of Nepalese human serum samples at their laboratory and providing us result. Authors would like to thank CDC, Rabies Laboratory, Atlanta USA. The help of Sukraraj Tropical Hospital, Central Veterinary Laboratory, Central Veterinary Hospital and Rabies Vaccine Production Laboratory in Kathmandu for providing serum samples is highly appreciated.