Tanzania Journal of Health Research Health User's Trust Fund (HRUTF) ISSN: 1821-6404 Vol. 12, Num. 1, 2011

Tanzania Journal of Health Research, Vol. 12, No. 1, January, 2010

Spatial and temporal distribution of rabies in the northern zone of Tanzania in the period of 1993-2002

E.S.SWAI*, W.E.MOSHY, J.E.KAAYA and P.F.MTUI

Veterinary Investigation Centre, P.O. Box 1068 Arusha, Tanzania

* Correspondence: Dr. E.S. Swai; E-mail: ESwai@gmail.com

Received 27 September 2009
Revised 16 December 2009
Accepted 17 December 2009

Code Number: th10010

Abstract

A retrospective study was carried out to investigate the occurrence and distribution patterns of rabies cases in northern Tanzania. Data on laboratory confirmed brain samples and associated case reports submitted to the Arusha Veterinary Investigation Centre, for a period of ten years (1993-2002) was retrieved and reviewed. A total of 98 suspected rabies brain specimens from different animal species and geographical areas were submitted and processed during the period under review. Rabies was confirmed using Fluorescent Antibody Technique test. Of the 98 brain specimens processed, 65(66.3%) were confirmed to be rabies cases. Canine rabies accounted for 73.8% of the cases and was in diagnosed in dogs (43), jackals (4) and hyenas (1). Rabies in wildlife accounted for 5 out of 48 canine confirmed cases. Most of the cases were from Arusha (20) followed by Arumeru (19), Ngorongoro (9) and Moshi (8) districts. Rabies positive cases in other animal species were in the following order of frequencies: bovine (9 out of 11); feline (5 out of 10); equine (1 out of 2); caprine (2 out of 2). One porcine brain specimen was rabies negative. The high proportion of rabies positive cases confirmed suggests the level of their endemicity in the northern region of Tanzania. Moreover, the findings highlights the need for sustained surveillance and institution of control measures among dog population and awareness creation particularly among general public and children whom are at high risk of contracting rabies because of their close contact with dogs.

Key words: rabies, spatial, temporal, pattern, fluorescent antibody test, rabies, Tanzania

Introduction

Rabies is a highly fatal neurological zoonotic disease of all warm-blooded animals caused by viruses of the genus Lyssavirus in the family Rhabdoviridae (Pringle, 1991).  Humans are usually infected when they are bitten by an infected animal or exposed to its saliva or central nervous system tissues (WHO, 2008). The disease is invariably fatal if post-exposure prophylaxis is not administered prior to the on set of severe symptoms (Nigg & Walker, 2009). Globally, it is estimated that more than 55,000 people die of rabies each year, with 97% of these deaths been associated with dog bites (WHO, 2008). The disease is present on nearly every continent of the world, but most human deaths occur in Asia (54%) and Africa (41%) (WHO, 2008). India has been reported as having the highest rate of human rabies in the world, primarily because of stray dogs (Nigg & Walker, 2009). In Tanzania, the mean number of officially reported human rabies deaths from 1990 to 1996 was 10.8 per year (Cleaveland et al., 2002).

Rabies is endemic in Tanzania (Rweyemamu et al., 1973; Magembe, 1985; Loretu, 1988; Majuva, 1988; Cleaveland & Dye, 1995).The disease was first reported in North Mara and Loliondo areas having been introduced from an outbreak in Kenya (Rweyemamu et al., 1973).  Rabies constitutes a serious public health problem in the northern regions namely Arusha, Manyaara, Kilimanjaro and Tanga and probably in Tanzania as a whole (Shayo et al., 2004). Currently rabies is endemic in most districts of the northern Tanzania, with over 70% of the districts reporting dog/animal bites cases in 2002 alone (Anon, 2002). Disease reporting and diagnosis is inadequate and the magnitude of rabies in the northern regions is not fully understood. 

Rabies is a zoonotic condition of public health importance especially in high risky groups such as veterinarian, paravets, public health workers and livestock keepers/handlers. Moreover, rural people and in particular children under  the age of 15 years are at  a higher risk of rabies, due to their close contact with dogs, and are more likely than adults to suffer multiple bites and scratches to the face and head, both of which carry a higher risk of contracting rabies. Furthermore, children are often unaware of the danger that dogs transmit rabies and may not tell their parents when a bite, lick, or scratch has occurred from an infected animal.

In Tanzania, the disease burden is largely unknown because patients with encephalitis following dog bites are rarely hospitalized and die at home. As a result, reliable data indicating the true public health impact of the disease are sparse or non-existent in many districts and regions (Cleaveland et al., 2002). That fact contributes to rabies often being considered insignificant by policy makers, and ultimately results in little motivation to implement disease control measures. Laboratory confirmation of rabies in domestic and wild animals is essential for a better understanding of the magnitude of the rabies problem, optimizing the use of human rabies post-exposure prophylaxis, and for evaluating the impact of control measures. The objective of this study was therefore, to review and report the findings of rabies cases as diagnosed and confirmed at the Veterinary Investigation Centre (VIC) in Arusha, Tanzania, during a ten-year period (1993-2002).

Materials and Methods

Study sites

Suspected rabies brain specimens were drawn from 5 animal species and 9 districts of the Arusha, Manyara and Kilimanjaro regions, north Tanzania. These nine districts which covers an area of 56,852 km² lies between latitude 2^o11’ and 6^o14’S and longitude 35^o11’ and 38^o26’E. The area receives an average annual rainfall of 1100mm which is bimodal in distribution. The long rains fall from March-May and the short rains fall from October–December. Temperatures vary between 13^oC and 31^oC throughout the year, the coldest month being July and warmest months being October and March, prior to the rains.

Collection, source and analysis of samples

Data on laboratory results of suspected rabies brain specimens that were collected and submitted to Arusha Veterinary Investigation Centre (VIC) and accompanied case reports from January 1992 to December 2002, were retrieved and reviewed. At the Arusha VIC, submitted brain samples were preserved and processed according to standard procedure i.e. preserved in 50% glycerol solution or on ice and examined by the fluorescent antibody test (FAT) for confirmation of rabies (Bourhy et al., 1989; Jayakumar et al., 1989; OIE, 1996, 2000). Due to laboratory capacity, histopathological investigation aimed at establishing presence of Negri bodies was not undertaken.

Data analysis

Laboratory results kept over the years under review were manually extracted from the centre record books. Retrieved information included source, animal species, case history, date of submission and laboratory results. Retrieved data were entered, managed and analysed using Microsoft Excel. Descriptive statistics generated included counts and frequencies. Graphical results were developed using Excel software programme (Microsoft Inc., USA).

Results

There was a total of 98 specimen submitted during the ten-year period 1993-2002. Highest submissions of 19 were in 2000 and the lowest of 3 were in 1996. Submissions were above average in 1993, 2000 and 2001, respectively (Figure 1). The majority of specimens were submitted from Arumeru (n=26) and Arusha Municipality (n=25). Others were from Ngorongoro (n=17), Moshi Municipality (n=10), Serengeti (n=9), Babati (n=4), Monduli (n=3), Simanjiro (n=3) and Hai (n=1).

There were 65 (66.3%) confirmed rabies positive cases for the ten year period with an average of 6.5 rabies cases per year. The lowest positive cases of only 50% were in 1993, 1994 and 1997 and in most cases coincided with the year with lowest submission. The highest rabies cases were in 1995 and 1999. Rabies positives were above average in 1996 and 1998 up to 2002 and this increase was due to different animal species (Figure 1; Table 1).

Table 1:  Confirmed cases of rabies in different host species from 1993-2002

Of 65 confirmed rabies cases, 48 (73.8%) were from canines (domestic dogs, jackals, hyena and wild dogs). This represents an average of 4.8 cases per year. In feline, a total of five brain specimens out of ten submitted over the period under review were positive, whereas in bovine, a total of nine out of twelve submitted were confirmed positive rabies cases. Rabies positive cases in other species were in the following order of frequencies: equine (one out of two) and caprine (two out of two). One porcine brain specimen was rabies negative. Ninety-four (96%) of all case histories were either associated with incidence of human or animal bites. Four (4%) of the specimens submitted had no history.

Table 2: Positive rabies diagnosis by district, 1993-2002

Most cases of rabies were diagnosed from specimens submitted from Arusha Municipality and Arumeru district (Table 2). The annual average submission rate was 2.5 and most of the case was from dogs. Of the submitted cases, 20(76.9%) were rabies positive. Nineteen (73%) of the twenty five submitted from Arumeru district were rabies positive. With the exception of Hai local government authority, Serengeti and Simanjiro districts had the lowest (<50%) rabies positive cases.

Discussion

The results show that the number of received brain specimen was lower and not comparable to the reported evidence of rabies basing on animal disease field report forms submitted regularly to the VIC in Arusha (Anon, 2002). The estimated submission rate of 9.8 brain samples per year is higher than the average of 5 recorded between 2000-2003 in Southern highland Zone in Iringa (Nsengwa & Maselle, 2004). The reason for the decrease in the number is difficult to explain, however, it appears to be multi-factorial in dimension. Difficulties in specimen collection; lack of equipment and reagents; poor storage, handling and transportation facilities; and inadequate financial resources are likely to be amongst potential reasons for this. Other potential reasons could be due to lack or little awareness from public on the importance of diagnosing rabies and the long distance range between area of rabies outbreak and the nearest veterinary investigation centre (Shayo et al., 2004). The observed high submission rates from Arusha Municipality and Arumeru is in part related to the closeness of these districts to the VIC. Arusha and Arumeru districts for the majority of the rabies positive cases in the zone. Most of the positive cases were in dogs. The low rabies positive cases in Simanjiro and Serengeti could be due to small sample size. The reasonably high submission rate from Ngorongoro and Serengeti was largely due to the efforts of Carnivore Project which has been operating in the two districts for the past 10 years. Almost all wild canine species samples came from these two districts in which the Ngorongoro Conservation Area and Serengeti National Parks, respectively, are located.

The apparent low submission rate detected in this study, justifies the importance of outreach programmes in order to increase community awareness and the need for laboratory diagnosis of rabies. Consistent with awareness creation, capacity building for field veterinary staff on the avenues of quality specimen collection, preservation and transportation deserve attention during routine field surveillance visits. Most of the district‘s based veterinary diagnostic centres are not well equipped with necessary tools to handle rabies suspected specimens (E. Swai, unpubl).

Of the submitted and examined specimen, two thirds were rabies positive. This apparently high rate of positive rabies confirms the magnitude of endemicity of this disease in the northern regions of Tanzania. Canine rabies accounted for the about three quarters of the cases and was in the dogs, jackals and hyenas. Canines, mostly dogs are known to be the main reservoir and source of infection (Rweyemamu et al., 1973; Cleaveland et al., 1998; Kitala et al., 2000). These findings underpin the fact and further confirm the perception that dog rabies predominates in parts of Africa, Asia, Middle East and Latin America (Mays & Aiello, 1998). The few cases of bovine, equidae and caprine and absence of porcine rabies, indicate that the species play a minor role in perpetuation of rabies in the region.

The dog and to a lesser extent cats are the main source animals for livestock infection. Cats are known to be susceptible to the rabies virus and often times, cases of cat rabies have outnumbered dog rabies in some countries (Mays & Aiello, 1998). Rabies in wild life accounted for 10.4% of 48 canine positives confirmed cases and a high proportion was due to jackal /hyena rabies.  The importance of wildlife in the spread of rabies has been reported in Tanzania (Mlengeya, 1999; Cleaveland et al., 2002). Cases of wild carnivore human bite are frequently reported in areas where wildlife co-exists with domestic animals and human beings (M. Kilewo, pers comm.).

Globally, rabies is considered to be a relatively insignificant human disease, accounting for only1% of deaths attributable to infectious diseases (Meslin et al., 1994). In Tanzania, only a few cases of rabies are reported annually, and most often are reported as animal bites due to inability of the health facilities to diagnose human rabies. Lack of diagnostic capacities is exacerbated by a poor Health Management Information System resulting into poor quality of data and under reporting of rabies cases (Rumisha et al., 2007). A new approach has recently been adopted in Tanzania to estimate human rabies deaths. A country-wide rabies DALY estimates has been extrapolated at 46,669 (Coleman et al., 2004).  However, the significant rabies positive samples revealed in this study suggest canine rabies is of great public health concern particularly to children who are comparatively at a higher risk. Some conservative estimate studies, based on official reported cases, have shown that the disability-adjusted life loss for rabies place the disease in eighty-sixth position with respect to public health burden (Fevre at al., 1999). The other negative impact of the disease is related to the high cost of human post-exposure treatment, fear and psychological trauma imparted to the disease victim and communities.

In Tanzania control of rabies has been based only on vaccinations, destruction of stray dogs and quarantines. Reproduction and habitat control have not been tackled.  Vaccination as a method of control has not been successful as annual rabies vaccination reports from 1980 to 1991 (MoAC, 1995) show immunisation coverage of 10% of the dog population, far below the WHO (1992) recommendations of 75%. Limitation of the current rabies control approaches include timely availability of vaccines, veterinary cost, poor compliance of dog owners in presenting their pet dog and cats for vaccination and inadequate reinforced legislation. Other potential limitation is impracticability of vaccinating wild carnivores and some of the available vaccines are contraindicated in cats.

In conclusion, this study has shown that rabies is still a serious public health problem in the northern regions of Tanzania. It is recommended that proper rabies control plans, surveillance and the current enforcement measures be revisited. The law pertaining to control of stray dogs and adherence to vaccination coverage should be put in place.

The permission of the Director of Veterinary Services, Tanzania to publish this work is gratefully appreciated. VIC colleagues are thanked for technical assistance.

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