**2. Epidemiology and immunization**

### **2.1 Measles virus detection strategies and sero-surveillance in Africa**

Following a successful polio laboratory platform, The Global Measles and Rubella Laboratory Network (GMRLN) was developed. As at 2018, there are presently 723 laboratories established in 164 countries. It was proposed that in all districts in WHO AFRO surveillance performance should target ≥2 cases of nonmeasles febrile rash illness per 100,000 population and ≥1 suspected measles case investigated with blood specimens in ≥80% of districts [16]. Case-based surveillance with laboratory confirmation of suspected measles cases is in place in many developing countries. Integrated Disease Surveillance and Response (IDSR) was established for aggregate reporting of 18 infectious diseases, including measles. Through the IDSR, aggregate numbers of suspected measles cases and deaths are reported weekly from districts to national level. Through measles case-based surveillance, suspected measles cases were investigated using case investigation form and laboratory testing of blood specimen. Specimens are tested using standard enzyme-linked immunosorbent assays for measles-specific immunoglobulin M (IgM) antibodies. Suspected measles case was defined as an illness with maculopapular rash and fever and one or more symptoms of cough, coryza or conjunctivitis, or where clinician suspects measles. Laboratory-confirmed measles case on the other hand is defined as suspected measles case with positive laboratory test result for measles specific IgM in the absence of measles vaccination within 30 days of specimen collection. An epidemiologically-linked case is suspected measles case having contact (or living in same district) with laboratory-confirmed measles case whose rash onset was within preceding 30 days. Clinically-compatible case is suspected measles case without laboratory test result or established epidemiological link. PCR detection is carried out in specific laboratories with technology for confirm hemagglutinin (H) and nucleoprotein (NP) gene of measles virus.

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*Measles in Developing Countries*

*DOI: http://dx.doi.org/10.5772/intechopen.84188*

widely in northern Africa [17, 26–28].

**2.4 Vaccination and herd immunity**

**2.3 MV complications in developing countries**

**2.2 Circulating genotypes and clades in Africa**

Measles virus is monotypic; however, genetic variations occur in the H and NP genes. Currently, the WHO recognizes 8 clades, A-H which consists of 24 genotypes and an additional provisional genotype, D11. Clades B, C, D, G and H each contain multiple genotypes (B1-3, C1-2, D1-10, G1-3 and H1-2) while clades A, E and F each contain single genotype (A, E and F) respectively [17, 18]. Epidemiological findings reveal circulation of several genotypes in Africa. Genotype A has been detected in South America, parts of China and South Africa over the last 40 years [19], and recently in a 3 year old child in Nigeria West Africa [20]. The most endemic genotype circulating in Africa is B3. Studies have shown clade B to be endemic in sub-Saharan Africa [21] with B3 genotype reported in Ghana, Gambia, Nigeria, Libya and Tunisia [20, 22, 23]. The measles viruses isolated in 1983 from Yaoundé, Cameroon, were designated as B1 genotype. However, in 2001 viruses belonging to B3 genotype were found in the country. B3 genotype has been reported in the Gambia. The B3 genotype (2001) in Cameroon were related to B3.1 subgroup, whereas the Gambian (1993) isolates corresponded to B3.2 subgroup. Geographical distribution for period 1993–2001 of these two viruses shows that B3.1 is found from Sudan to Nigeria and Ghana extending to Cameroon, whereas B3.2 genotype is found in West Africa. In Nigeria and Ghana, the viruses co-circulate [3, 14]. Nucleotide sequence analysis show strains from Senegal clustered in B3.1 and B3.3 sub-genotypes. Measles virus detected in Tunisia and Libya from 2002 to 2009 belonged to genotype B3. Viruses isolated from 2002 to 2007 and 2009 were subtype B3.1. Seven of isolates during 2008 and 2009 epidemic were divergent from the B3 isolates and can represent a new subtype of genotype B3 [21]. B3 strain circulates in Addis Ababa, Bahir Dar and possibly elsewhere in Ethiopia [24]. In a 2014 outbreak among refugees from Central African Republic in Cameroon, the genotype B3 found were similar to those circulating in Northern Cameroon in 2010–2011 [25]. Clade B viruses is reported to be endemic in central and western parts of sub-Saharan Africa while genotypes D2 and D4 has been continually detected in southern and eastern parts of Africa. D10 in Uganda is represented by Clade MVi/Kampala. UGA/51.00.1 with accession number AY923185.1. Genotype C2 is found to circulate

Measles is characterized by fever of 38°C or more; maculopapular rash of 3 days or more; with one or combination of coryza, cough, conjunctivitis and Koplik spots in the oral mucosa of measles' victims [29]. Mortality rates can exceed 10% in parts of the developing world. Sequela of measles includes giant cell pneumonia, inclusion body encephalitis and sub-acute sclerosing pan encephalitis [SSPE] [30]. A study carried out in the largest children's hospital in Ibadan-Nigeria in West Africa observed several complications ranging from bronchopneumonia (60%), heart failure (12%), gastroenteritis (11%), protein losing malnutrition (8%), encephalitis (5%), croup (2%) and dehydration (2%) [10], whereas bacterial complication is the

After routine and catch-up vaccinations in 2005 and 2006, as well as follow-up vaccination by 2008 in Nigeria, remarkable level of protection was observed in children. This is attributed to immunological dynamics which is an after-effect of these campaigns [32]. Herd immunity varies between heterogeneous populations in

usual cause of death when measles kills malnourished children [31].

*Viruses and Viral Infections in Developing Countries*

**2. Epidemiology and immunization**

**2.1 Measles virus detection strategies and sero-surveillance in Africa**

glutinin (H) and nucleoprotein (NP) gene of measles virus.

Following a successful polio laboratory platform, The Global Measles and Rubella Laboratory Network (GMRLN) was developed. As at 2018, there are presently 723 laboratories established in 164 countries. It was proposed that in all districts in WHO AFRO surveillance performance should target ≥2 cases of nonmeasles febrile rash illness per 100,000 population and ≥1 suspected measles case investigated with blood specimens in ≥80% of districts [16]. Case-based surveillance with laboratory confirmation of suspected measles cases is in place in many developing countries. Integrated Disease Surveillance and Response (IDSR) was established for aggregate reporting of 18 infectious diseases, including measles. Through the IDSR, aggregate numbers of suspected measles cases and deaths are reported weekly from districts to national level. Through measles case-based surveillance, suspected measles cases were investigated using case investigation form and laboratory testing of blood specimen. Specimens are tested using standard enzyme-linked immunosorbent assays for measles-specific immunoglobulin M (IgM) antibodies. Suspected measles case was defined as an illness with maculopapular rash and fever and one or more symptoms of cough, coryza or conjunctivitis, or where clinician suspects measles. Laboratory-confirmed measles case on the other hand is defined as suspected measles case with positive laboratory test result for measles specific IgM in the absence of measles vaccination within 30 days of specimen collection. An epidemiologically-linked case is suspected measles case having contact (or living in same district) with laboratory-confirmed measles case whose rash onset was within preceding 30 days. Clinically-compatible case is suspected measles case without laboratory test result or established epidemiological link. PCR detection is carried out in specific laboratories with technology for confirm hemag-

Despite the comprehensive WHO and United Nations International Children Emergency Fund's (UNICEF's) measles-reduction strategy, and partnership of international organizations for measles mortality reduction, certain countries continue to face recurrent epidemics [5]. The optimal age for infantile measles vaccination is an important since maternal antibodies may neutralize the vaccine antigen before specific immune response develops. Delaying vaccination on the other hand may increase risk of complicated disease [6]. Measles vaccine effectiveness is 84% when administered at 9–11 months of age and 93% when given at ≥12 months of age [7]. First dose of measles-containing vaccine (MCV1) given at 9 months of age was introduced into the Expanded Programme on Immunization (EPI) in 1977 [8]. Since >93–95% population immunity is required to prevent measles epidemics, the WHO recommends all children receive two doses of measles vaccine [9]. In Nigeria just like in many developing countries, children are given monovalent measles vaccine at 9 months of age in the EPI [10]. In 2010 and continuing through 2014, DRC experienced the largest nationwide measles outbreak in Africa [11–13]. DRC is a key country for regional elimination efforts because of its large population, central location with nine international borders, and persistent reservoir of circulating measles viruses [14]. The Reaching Every District (RED) approach to strengthening immunization services has been implemented beginning in some developing countries like Democratic Republic of Congo (DRC). A second opportunity for measles vaccination, nationwide measles supplementary immunization activities (SIAs) using a phased approach intended to cover the country every 3 years [15].

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