Human Ehrlichioses and Rickettsioses in Cameroon

Human ehrlichioses and rickettsioses are important arthropod borne infectious diseases which are transmitted by ticks, mites, lice and fleas. Infections result in mild to fatal outcomes, with clinical presentations that resemble other tropical infectious diseases such as malaria making clinical diagnosis difficult. Despite recognition as important causes of lifethreatening diseases in the United States, the geographic distribution of these diseases worldwide remains undefined due to their recent emergence, challenges in diagnosis and lack of comprehensive epidemiological studies needed to determine incidence in developing countries. Recently, the transfer of technological developments to other parts of the world especially developing countries has encouraged basic epidemiological inquiry and generated scientific interest in understanding the epidemiology of these tick borne diseases and their role as causes of undifferentiated febrile illnesses. In this chapter, we review the current knowledge of human monocytotropic ehrlichiosis (HME) and spotted fever rickettsiosis (African tick bite fever) in Cameroon.


Introduction
Human ehrlichioses and rickettsioses are important arthropod borne infectious diseases which are transmitted by ticks, mites, lice and fleas. Infections result in mild to fatal outcomes, with clinical presentations that resemble other tropical infectious diseases such as malaria making clinical diagnosis difficult. Despite recognition as important causes of lifethreatening diseases in the United States, the geographic distribution of these diseases worldwide remains undefined due to their recent emergence, challenges in diagnosis and lack of comprehensive epidemiological studies needed to determine incidence in developing countries. Recently, the transfer of technological developments to other parts of the world especially developing countries has encouraged basic epidemiological inquiry and generated scientific interest in understanding the epidemiology of these tick borne diseases and their role as causes of undifferentiated febrile illnesses. In this chapter, we review the current knowledge of human monocytotropic ehrlichiosis (HME) and spotted fever rickettsiosis (African tick bite fever) in Cameroon.

Etiologic agents
Ehrlichioses are diseases caused by small (approximately 0.4-1.5 μm diameter) Gram negative, obligately intracellular bacteria belonging to the genus Ehrlichia of the family Anaplasmataceae, Order Rickettsiales and the alpha sub-division Proteobacteria (Dumler et al., 2001). Although they have a characteristic Gram negative cell wall structure, they lack the necessary enzymes to synthesize cell membrane components such as lipopolysaccharide and peptidoglycan (Lin & Rikihisa, 2003). As intracellular pathogens, Ehrlichia reside in cytoplasmic membrane-bound vacuoles inside host cells (granulocytes or monocytes) forming microcolonies called morulae, derived from the Latin word "morus" for mulberry (Popov et al., 1995;Paddock et al., 1997;Ismail et al., 2010). These morulae (ranging in size from 1.0 to 6.0 µm in diameter) may contain 1 to >40 organisms of uniform or mixed cell types (Popov et al., 1995;Rikihisa, 1999). Organisms in the family Anaplasmataceae were first described in 1910 when Theiler described Anaplasma marginale, the etiologic agent of an economically important and severe disease of cattle (Mahan, 1995). This discovery was followed shortly thereafter by the description of E. ruminantium (formerly Cowdria ruminantium) by Cowdry in 1925; E. canis by Donatien and Lestoquard in 1935;and A. phagocytophilum (formerly E. phagocytophila) by Gordon in 1940. Hence, the genus Ehrlichia was established in 1945 in honour of the German microbiologist Paul Ehrlich (Uilenberg, 1983). Ehrlichia species cause significant diseases in their natural hosts (livestock and companion animals) and emerging zoonoses in humans . The first human ehrlichial infection (sennetsu fever) was reported in 1953 ( Rapmund, 1984;Dumler et al., 2007). Sennetsu fever, caused by Neorickettsia sennetsu, was identified in Japan and Malaysia (Dumler et al., 2001;Dumler et al., 2007). However, recent phylogenetic reclassifications based on molecular analysis revealed that E. sennetsu is not a member of the Ehrlichia genus (Dumler et al., 2001). Presently, the genus Ehrlichia consists of five recognized species including E. canis, E. chaffeensis, E. ewingii, E. muris, and E. ruminantium, all of which are at least 97.7% similar in 16S rRNA gene sequence (Perez et al., 1996;Paddock et al., 1997;Dumler et al., 2001;Perez et al., 2006). Ehrlichiae have relatively small genomes (0.8-1.5 Mb) with low G+C content and a high proportion of non-coding sequences but can synthesize all nucleotides, vitamins and cofactors (Dunning et al., 2006). They also have small subsets of genes associated with hostpathogen interactions (Ismail et al., 2010). E. chaffeensis have immunodominant outer membrane proteins (OMP-1/MSP2/P28) (Ohashi et al., 1998;Yu et al., 2000;Huang et al., 2008), and in infected macrophages ehrlichiae express the p28-Omp 19 and 20 genes as dominant protein products Peddireddi et al., 2009). Ehrlichiae also express several targets of the humoral immune response including tandem repeat and ankyrin repeat containing proteins (Yu et al., 1997;Sumner et al., 1999;McBride et al., 2003;McBride et al., 2007). E. chaffeensis, a human pathogen that was first recognised in the United States in 1986 and isolated in 1991 ( Maeda et al., 1987;Dawson et al., 1991) is the cause of human monocytotropic ehrlichiosis (HME) (Anderson et al., 1992), a moderate to severe disease with a case fatality rate of 3% (Fishbein et al., 1994;. E. chaffeensis is an obligately intracellular bacterium that primarily infects mononuclear leukocytes and replicates by binary fission. E. chaffeensis morulae can be detected in peripheral blood smears obtained from infected patient s w h e n o b s e r v e d w i t h a l i g h t m i c r o s c o p e (Rikihisa, 1991). When tissues (including clinical samples), mononuclear leucocytes or cell lines of mammalian origin infected with E. chaffeensis are viewed by electron microscopy, two distinct morphologic cell types are identified: a predominantly coccoid form which has a centrally condensed nucleoid DNA and ribosomes (dense-cored cells) measuring between 0.4 and 0.6 µm in diameter and reticulate or the coccobacillary form, which measures about 0.4 to 0.6 µm by 0.7 to 1.9 µm (Paddock et al., 1995;Popov et al., 1997).

Vectors and reservoirs
Investigative studies following the discovery of E. chaffeensis in the late 1980s revealed that the agent is transmitted to humans by the tick Amblyomma americanum, commonly referred to as the lone star tick which has a limited geographic distribution to the United States (Anderson et al., 1993). Molecular analysis (PCR) has demonstrated E. chaffeensis DNA in adult A. americanum ticks collected from different states. The increased recognition of E. chaffeensis as an emerging problem has evoked renewed interest in this and other tick borne diseases, and this has stimulated epidemiologic investigations of this pathogen and its vector in other regions where the tick A. americanum is not found. Results not only indicate www.intechopen.com that E. chaffeensis has a wider distribution than the United States (Ndip et al., 2010), but also indicates that the pathogen exists outside of the known range of A. americanum and is harbored by other tick species. These tick species include Ixodes pacificus in California (Kramer et al., 1999), Dermacentor variabilis in Missouri (Roland et al., 1998), Ixodes ricinus in Russia (Alekseev et al., 2001), Amblyomma testudinarium in China, (Cao et al., 2000), Haemaphysalis longicornis (Lee et al., 2003), and Ixodes persulcatus  in Korea. Studies carried out by Ndip and colleagues in Cameroon identified Ehrlichia chaffeensis in Rhipicephalus sanguineus ticks. R. sanguineus, commonly known as the brown dog tick ( Figure 1a) is a species that infests canids worldwide. In one study in Limbe, Cameroon, a very high prevalence of E. chaffeensis was detected in R. sanguineus ticks infesting dogs inhabiting one kennel (Ndip et al., 2010). E. chaffeensis DNA was detected in 33 (56%) of 63 R. sanguineus ticks collected from five dogs as opposed to 4 (6%) ticks infected with E. canis. Furthermore, co-infection with more than one pathogen was not uncommon. The E. chaffeensis strain circulating in Cameroon is similar to the North American strain AF403710 based on the analysis of the 378 bp fragment of the disulphide bond formation (Dsb) protein gene (Ndip et al., 2010). Earlier reports revealed E. canis, E. chaffeensis, and E. ewingii in R. sanguineus ticks collected from 51 dogs from different localities in Cameroon (Figure 2), suggesting that dogs could be a reservoir for E. chaffeensis and that R. sanguineus is the probable vector (Ndip et al., 2007). In the United States, the white-tailed deer (Odocoileus virginianus) has been recognised as the primary natural reservoir of E. chaffeensis (Dugan et al., 2000). However, animals such as goats, dogs, and coyotes have also been identified as reservoirs which could play a limited role in the transmission of the pathogen to humans (Breitschwerdt et al., 1998;Dugan et al., 2000;Kocan et al., 2000). Unlike rickettsial species, ehrlichial species are not transmitted trans-ovarially (ie., larvae are uninfected) suggesting that the pathogen is maintained transstadially after the infection is acquired (Ismail et al., 2010). Although the reservoirs for E. chaffeensis in Cameroon have not yet been conclusively identified, preliminary studies detected antibodies reactive to E. chaffeensis in 56% of goats analysed suggesting a probable role of goats in maintaining the pathogen in nature. Moreover, E. chaffeensis DNA was detected in 17% of ticks collected from these animals (Ndip, unpubished data). www.intechopen.com

Epidemiology
The epidemiology and ecology of HME worldwide is not well documented. Since its description in 1986 more than 1000 cases of HME from at least 30 U.S. states have been reported to the Centers for Disease Control and Prevention in Atlanta, Georgia with nearly all occurring in the southeastern and south-central United States where the vector, A. americanum is common (Paddock & Childs, 2003;Dumler et al., 2007). However, the evidence of the disease and/or the pathogen is increasingly being reported in other parts of the world. This includes Africa (Uhaa et al., 1992;Ndip et al., 2009;Ndip et al., 2010), Israel (Dawson et al., 1991;Keysary et al., 1999;Brouqui & Dumler, 2000), Latin America (Gongora-Biachi et al., 1999;Calic et al., 2004;) and Asia (Heppner et al., 1997;Cao et al., 2000;Heo et al., 2002;Kim et al., 2003;Park et al., 2003, Lee & Chae, 2010. In Cameroon, HME has been identified in patients along the coast of Cameroon, in Buea  Figure 2). HME was observed in both males and females as well as in children and adults although results suggested that older age was a risk factor for the disease (Ndip et al., 2009). The majority of the patients were adults which suggests that exposure to infected ticks may have occurred during outdoor activities such as farming. Another risk factor is that of owning a companion or domestic animal since most Cameroonian HME patients indicated they had tick-infested pets and domestic animals.

Microbiological diagnosis
The diagnosis of HME requires specialized microscopy equipment and skills which are not readily available in many diagnostic laboratories. Several methods have been proposed for the diagnosis of HME (Paddock & Childs, 2003;Ismail et al., 2010), including serologic tests such as immunofluorescent assay (IFA), western immunoblot employing specific proteins or ehrlichial whole cell antigens or the recently developed Ehrlichia recombinant protein or peptide ELISA for detection of the antibody Luo et al., 2010;O'Connor et al., 2010). Though these tests can be used to confirm diagnosis retrospectively, some patients may not sero-convert during the early days of the disease and cannot be diagnosed with serologic tests. However, collecting paired sera (at acute and convalescent phases of illness) is confirmatory as a four-fold rise in titer indicates current infection. However, this www.intechopen.com always presents a problem because patients who recover may not return to the hospital for follow up. Moreover, another issue with the interpretation of serological tests such as IFA is cross-reactive antibodies against other organisms, including Anaplasma species. PCR has also been employed to identify ehrlichial DNA in acutely ill patients when antibodies have not reached detectable levels. Several genes have been proposed and used including the VLPT gene (TRP32), TRP36, 16S rRNA, the TRP120, the Dsb, 28-kDa outer membrane protein gene have been used as genus or species specific targets (Yu et al., 1999;Doyle et al., 2005). IFA, western blot and PCR have been used to study the prevalence of ehrlichiae in blood of acutely ill patients, reservoirs, or in suspected tick vectors and anti-ehrlichial antibody in sera (Ndip et al., 2005;Ndip et al., 2007;Ndip et al., 2009;Ndip et al., 2010). Figure 3 shows IFA photomicrographs of whole cell of E. chaffeensis reacting with antibodies in an HME patient serum. A rapid method to detect E. chaffeensis is the observation of morulae in smears of peripheral blood buffy coat using the Diff Quik or Giemsa stain. However, this technique is very insensitive, and morulae are detected in leukocytes in only 10% of HME patients.

Treatment
The drug of choice for the treatment of E. chaffeensis infection is the tetracyclines (particularly doxycycline) and their derivatives. Generally, between 1 and 3 days after a patient with HME commences treatment with doxycycline, the patient becomes afebrile (Olano & Walker, 2002). However, treatment may continue for up to 10 days or at least 3 days after the patient becomes afebrile (Chapman et al., 2006). Clinical experience and invitro susceptibility testing of E. chaffeensis to some classes of antibiotics have revealed that fluoroquinolones, penicillins, aminoglycosides, macrolides and cotrimoxazole are not effective therapeutics (Dumler et al., 1993;Brouqui & Raoult, 1994;

The Genus Rickettsia
Rickettsial organisms are Gram-negative bacteria belonging to the order Rickettsiales, Family Rickettsiaceae and the Genus Rickettsia. They are strict intracellular parasites that are transmitted by arthropods including fleas, lice, mites and ticks (Kelly et al., 1992). These organisms are typically short rods (coccobacilli) measuring about 0.8-2.0µm in length and 0.3-0.5µm in diameter. They exhibit most of the biochemical and morphological characteristics of the Gram-negative cell (Gimenez, 1964;La Scola & Raoult, 1997). Based on antigenic characteristics, species of the genus Rickettsia have been divided into three groups; namely the typhus group (TG), the spotted fever group (SFG) and the transitional group (TRG). The TG has two members (R. prowazekii and R. typhi), which are mainly transmitted by lice and fleas, respectively (Raoult & Roux, 1997). The largest of the antigenic groups is the SFG that is made up of the tick-transmitted pathogens (except R. bellii and R. canadensis) (Parola et al., 2005). It has been grouped into several genogroups based on the 16S rRNA, the gltA, ompA, ompB and sca2 sequences. These groups include the R. rickettsii group, the R. massiliae group and R. helvetica group. The transitional group includes R. akari, R. australis, and R. felis. There are many ancestral organisms including R. canadensis and R. bellii (Parola et al., 2005), as well as numerous rickettsiae in herbivorous insects, and other hosts (leaches and amoeba). Also in the family Rickettsiaceae is Orientia tsutsugamushi, which is transmitted by Leptotrombidium deliense (Tamura et al., 1995). Rickettsial organisms are of worldwide occurrence, although species/vector differences may exist along various geographical lines. In Africa, several species have been reported. These include R. conorii Malish strain, the cause of Mediterranean spotted fever or "boutonneuse fever". It was first documented in Tunis (Conor & Bruch, 1910), and today the disease continues to be reported in Tunisia (Romdhane et al., 2009;Sfar et al., 2009) and South Africa. The infection has the characteristic of a papular rash, in addition to an eschar at the site of the tick bite (Anton et al., 2003). The pathogen is transmitted by R. sanguineus ticks, and is considered an urban disease (Font & Segura, 1983). Human infections with another strain of R. conorii (Israeli spotted fever strain) have been recently documented in Tunisia (Znazen et al., 2011). R. conorii Astrakhan strain is the cause of Astrakhan fever first detected in Astrakhan, Russia in the 1970s and transmitted by R. sanguineus and R. pumilio ticks (Parola et al., 2005). The Astrakhan strain has also been isolated from a patient in Chad . R. sibirica mongolitimonae strain was identified in Hyalomma truncatum ticks in Niger in 2001 (Parola et al., 2001) and the first human case in Africa was documented in South Africa (Pretorius & Birtles, 2004). Other cases have been reported to have been acquired in Algeria (Fournier et al., 2005) and Egypt . Another species, R. aeschlimannii, which was first isolated in H. marginatum ticks in Morocco (Beati et al., 1997) and later detected in H. marginatum rufipes in Mali and Niger, have been known to cause infections in tourists returning from Morocco and South Africa (Parola et al., 2001). R. massiliae, first isolated from R. sanguineus ticks in Marseille, France (Parola et al., 2005) was detected in R. muhsame, R. lunalatus and R. sulcatus from Central African Republic (Dupont et al., 1994) and in R. muhsame ticks collected from cattle in Mali 2001) and Ivory Coast (Berrelha et al., 2009). Rickettsia felis is a recently identified pathogen which was first detected in Ctenocephalides felis fleas (Bouyer et al., 2001). In Africa, the agent has been reported in Ivory Coast (Berrelha et al., 2009) andSenegal (Socolovsch et al., 2010), and human infections have been reported in Kenya (Richards et al., 2010). Rickettsia africae, the etiologic agent of African tick bite fever appears to be the most prevalent rickettsiosis in Africa. The disease was first reported in Mozambique and South Africa (McQuiston et al., 2004). The first isolate (R. africae strain ESF-5), was recovered from A. variegatum ticks in Ethiopia although it was only characterized as R. africae later . The agent was later isolated in A. hebraeum ticks in Zimbabwe in 1990, and in 1992, the first isolate from a patient was obtained Kelly et al., 1994). The pathogen has been detected in many other African countries including Senegal , Ethiopia (Stephany et al., 2009) and Cameroon (Ndip et al., 2004a;Ndip et al., 2004b). In the following, we give a synopsis of our current knowledge of African tick bite fever in Cameroon.

Causative organism
R. africae, a member of the SFG is the only species that has been detected in Cameroon. The organism which measures about 0.4 µm by 1.0 µm, has an outer slime layer and a trilaminar cell wall which contains immunogenic lipopolysaccharide antigens responsible for crossreactivity with the other SFG rickettsiae (Hechemy et al., 1989;Kelly et al., 1996). Like other Gram-negative organisms, rickettsiae have outer membrane proteins (dubbed OmpA and OmpB) present as species-specific antigens (Fournier et al., 1998;Roux & Raoult, 2000). The organism lives freely in the cytoplasm and usually infects endothelial cells. According to phylogenetic studies, this rickettsial species, which belongs to the R. rickettsii group is closely related to R. parkeri in North America and R. sibirica in northeast Asia (Parola et al., 2005).

Tick vectors and reservoirs
R. africae is a tick-borne pathogen, and ticks serve both as vectors and reservoirs. The pathogen is maintained in the tick through trans-stadial and trans-ovarial transmission, and this situation indicates the potential for transmission to humans by all stages (larvae, nymphs, and adults) of the feeding ticks. Ixodid ticks (hard ticks) of the genus Amblyomma have been recognized as the vectors (Kelly, 2001). In Cameroon, A. variegatum (Figure 1b) www.intechopen.com has been identified as the potential vector with about 75% of ticks (male and female) collected from cattle found to be infected with R. africae (Ndip et al., 2004b). Reports from other studies have indicated that R. africae infection in Amblyomma ticks frequently has a high prevalence (up to 100%) reported in ticks collected in some disease-endemic countries (Dupont et al., 1994;Parola et al., 2001). Like any other tick borne disease, the ecological characteristics of the vector influence the epidemiology of the disease. The ticks are usually found all year round, but they peak during and after the rainy season when humidity is very high . Ambylomma are predominantly cattle ticks, and infestation of cattle can be very high . A. variegatum, commonly found in central and west Africa typically enjoys a wide variety of different habitats although they have a preference for semi-arid and humid areas with tall grass, trees, and/or bush cover. These ticks usually quest on vegetation and would usually attack legs although they may crawl to other areas such as groin and perineum where they attach (Jensenius et al., 2003).

Clinical presentation
Since the description of ATBF in 1992, most of the knowledge available regarding the disease has been documented in travelers who become infected with R. africae during travel in Africa. After inoculation from a tick bite, the bacteria invade the vascular endothelial system causing a focal or disseminated vasculitis. Endothelial cells of small blood vessels become infected leading to the destruction of the endothelial cells (Toutous-Trellu et al., 2003) of the host where they have multiplied and eventually injured the host cells, leading to the disease symptoms. Multiple eschars typical of ATBF develop at the sites of tick bite, and following an incubation period between 5 and 7 days (up to two weeks in some cases), after the tick bite a febrile illness develops . In most cases, symptoms of ATBF are usually mild and include headaches, nausea, chills, myalgia, lymphadenopathy and prominent neck ache (Jensenius et al., 2003;Raoult et al., 2001). Although there have been some controversies over the differences in the clinical presentations of African tick bite fever, our study of acutely ill patients in Cameroon revealed that the some individuals may manifest severe symptoms while in others the symptoms are mild. However, symptoms reported include fever >38°C (100%), headache (71%), myalgia (71%), arthralgia (57%), rash (15%) and pulmonary signs (28%).

Epidemiology
ATBF has been recognized as an emerging problem in sub-Saharan Africa, especially for international travelers to rural areas (Jensenius et al., 2003). Most of the victims reported are tourists who visit game reserves or participate in outdoor activities such as running, trekking and hiking in forested areas, usually inhabited by Amblyomma ticks. The patients acquire the disease in rural Africa, but most often symptoms manifest only after they have returned to their various countries in Europe and America. The first report suggesting that rickettsiosis could be prevalent in Cameroon was published in 1968 (Maurice et al., 1968). The report based on a serologic survey that used an unreliable technique demonstrated rickettsial antibodies in cattle and humans in the northern region of Cameroon and in other animals in the south of the country ( Maurice et al., 1968;Le et al., 1977). Efforts to determine the epidemiology and ecology later re-emerged in 2004 when anti-rickettsial IgM antibodies were detected in some Cameroonian patients along the coastal region of Cameroon (Ndip et www.intechopen.com al., 2004a). These results were further confirmed by detection of R. africae DNA in about 6% of acutely ill febrile patients (Ndip et al., 2004b). Human infections or the agent has been detected in all regions of southern Cameroon where epidemiologic investigations have been made (Figure 3). According to these studies, age appeared to be a risk factor of acquiring the disease, and it is suggested that activities such as game hunting usually constitutes a risk factor (Ndip et al., 2011). Other activities which could predispose to infection include cattle rearing and exposure to tick habitats. Cameroon is a sub-saharan tropical country with a vast equatorial forest providing a good habitat for ticks (especially A. variegatum ticks). Individuals residing in lowland rainforest habitats have a higher risk of acquiring ATBF probably because these habitats are ideal for A. variegatum ticks because of their moderate canopy cover, providing microclimates favoring tick survival (Ndip et al., 2011). Although ATBF has been shown to be prevalent in the southern part of Cameroon (Figure 2), the actual epidemiology of the disease through wider disease surveillance needs to be documented.

Diagnosis
Diagnosis of ATBF can be achieved by either serological analysis of acute and convalescent serum samples or molecular detection of the DNA of the bacterium by real-time or conventional PCR. Target genes that have been utilized include the rickettsial gltA and ompA genes. For serological diagnosis, the indirect immunofluorescent test has been used in conjunction with western blot assay to detect antibodies reactive with whole cells or specific proteins of cell lysates of R. africae. However, these tests are not very reliable in distinguishing species because cross-reactivity may be observed among the SFG rickettsiae. However, some authors have proposed that a fourfold or greater titer for R. africae compared to other species is confirmatory Ndip et al., 2004a). The western immunoblot assay can also be used to detect antibodies against species-specific OmpA and OmpB proteins.

Treatment
The drug of choice for the treatment of ATBF is doxycycline (100 mg twice daily) for 3-7 days. In-vitro studies also indicate that R. africae is susceptible to tetracyclines, fluoroquinolones, some macrolides and chloramphenicol (Rolain et al., 1998). Mild cases of ATBF have also been shown to recover naturally (Jensenius et al., 1999).

Prevention of ehrlichiosis and rickettsiosis
Studies in Cameroon indicate that one risk factor for contracting E. chaffeensis infection and ATBF appears to be exposure to potential tick vectors. Many reports involving acquisition of rickettsial diseases have also indicated that exposure to ticks during safari tours and visit to parks constitute an important risk factor. Therefore, an important method of preventing ehrlichiosis and rickettsiosis is by reducing contact with infected ticks. Personal protective measures are quite important, including wearing light colored clothes when walking in tick infested areas, using insect repellents and examination of clothing after a visit to a tick infested area, and prompt removal of attached tick can all reduce the risk of infection. Companion animals and other domesticated animals should be taken care of and tick infestation controlled.

Conclusions
These data emphasize the importance of ehrlichiosis and ATBF as prevalent diseases in an indigenous Cameroonian population. Although these diseases present as febrile illnesses, they are rarely considered when evaluating patients with acute, undifferentiated febrile illnesses. This situation can be attributed in part to lack of adequate knowledge of the epidemiology and ecology of the disease to prompt diagnosis; unavailability of specific laboratory tests, equipment, and expertise and also the limited economic resources. Sharing new knowledge on these diseases and techniques to facilitate diagnosis are important factors that can change the types and frequencies of diseases diagnosed in febrile patients and necessitate surveillance for these diseases. Future efforts will attempt to address other issues requiring investigations such as the full description of the clinical spectrum of these diseases in African patients and risk factors for severe illness.