Historical Perspective of Arboviruses in Mozambique and Its Implication for Current and Future Epidemics

Abstract

Mozambique is a tropical country situated in the Southern part of Africa, a region where data on the burden and epidemiology of arbovirus is presently quite scarce although the frequency of outbreaks caused by arboviruses is rapidly increasing. Outbreaks of dengue fever have been reported in Mozambique, Angola and Tanzania and a recent unprecedented outbreak of Yellow fever has been recorded in Angola. These new outbreaks collectively suggest that arboviruses, and specifically flavivirus infections, are endemic in Mozambique.

Although recent data on arbovirus activity is scarce, the work of Kokernot et al. [R.H. Kokernot, K.C. Smithburn, A.F. Gandara, B.M. Mc’Intosh and C.S. Heymann Anais Inst Med Trop (1960), 17:201–230] describes seroepidemiological and entomological studies carried out in several parts of Mozambique during the 1950s. Complementary seroepidemiological investigations on arboviruses that were conducted in the early 1980s also found serological evidence of several arboviruses which included Dengue, Chikungunya, Zika, Rift Valey Fever, Sinbdis virus, Wesselsbron, Bunyamwera, Pongola and Bawamba Fever and Yellow Fever.

Notably the first description of Chikungunya virus in 1952–1953 in Tanzania also included reported cases in northern Mozambique. Furthermore, DENV serotype 3 was for the first time described in northern Mozambique in 1984 and 1985. Since several arboviral infections result in acute self limiting fever they have remained unsuspected for several decades. However, it is well known that during the 1980’s intensive malaria control initiatives which included massive distribution of bed nets, community education and indoor and outdoor spraying campaigns were implemented. It is possible that these measures may have influenced the epidemiology of arboviruses. However, the impact of these interventions in controlling the spread of arboviruses is not known.

In conclusion, the old literature on arboviruses in Mozambique is relevant for assessing the gaps and current risk of occurrence of these pathogens at the region, particularly in a time in which they are spreading worldwide.

Discussion of Chapter 2 in Dengue and Zika: Control and Antiviral Treatment Strategies

This discussion was held at the 2nd Advanced Study Week on Emerging Viral Diseases at Praia do Tofo, Mozambique.Transcribed by Hilgenfeld R and Vasudevan SG (Eds); approved by Dr. Eduardo Samo Gudo.

• Aravinda de Silva: Just a quick comment about those Dengue 3 strains from the mid 1980s and their importance for Mozambique, because we showed subsequently that those strains were first described in Mozambique. I think some of those isolates came from Chinese workers in Mozambique and they spread it to the Indian subcontinent. In fact, the first major epidemic of severe Dengue caused by serotype 3 in the Indian subcontinent was very closely related to those strains from Mozambique. And then subsequently, those same strains were introduced into Panama and Nicaragua. And the severe Dengue epidemics in Latin America were also caused by a very close relative of the Mozambique viruses and so this highlights the importance of the circulating strains here in Mozambique. What kind of work is going on in terms of looking at enzootic cycles? For Dengue 3, we still do not know the sylvatic cycle – the non-primate cycle. Also for Chikungunya virus, you indicated that very early isolates came from this part of the world. Is there any work being done in this area?

• Eduardo Samo Gudo: Not yet. This is the first and only description of Dengue 3 in Mozambique as you can see in the map in my presentation. So nothing happened after that and it’s unclear and we do not know if we eliminated DENV3 from Mozambique.

• Aravinda de Silva: In terms of understanding the enzootic cycles of Dengue and Chickungunya – it may be an important area to focus in terms of non-human primate studies.

• Gao George: So where did the strains in Mozambique come from?

• Aravinda de Silva: That strain was first described in East Africa in Mozambique. It was subsequently described in Kenya, it went up to Somalia. It moved into the Indian subcontinent, where the very first description of the 1985 isolates came from.

• Subhash Vasudevan: So you said it came from China?

• Aravinda de Silva: No, I thought the Mozambican isolates came from Chinese workers in Mozambique, who got very sick, who got something like severe Dengue. But they were here working in Mozambique.

• Maurice Demanou: It is incredible, because the figures you presented are similar to the picture in Cameroon. But in the 60’s there was a lot of research on arboviruses done by medical research institutes. Later on in the 80’s, probably because of the outbreak of HIV, the arbovirus surveillance ceased. Even though there were some surveillances on yellow fever, nothing at all was done for other arbovirus research. In the year 2000, with the spread of epidemic arboviruses worldwide, people started to be interested. I think we have the same problem in Cameroon, but I do not know how you explain the 40 years’ gap in the attention.

• Félix Rey: Is there a political will now to change the situation and focus more on arboviruses?

• Eduardo Samo Gudo: Arboviruses are seriously neglected in Mozambique, as malaria, tuberculosis and HIV are the leading cause of morbi-mortality in the country and will for sure be the focus of intervention for many decades to come. Not just in Mozambique, this is similar in many countries in Africa. When we raise the issue of arboviruses, we are simply asked the question “How many people die per year because of Dengue and other arboviruses and how many from malaria, tuberculosis and HIV?” The fact is that it is much less than malaria, tuberculosis and HIV, so that is the end of he conversation.

• Subhash Vasudevan: What about co-infections of malaria with Chickungunya or Dengue?

• Eduardo Samo Gudo: There is high coinfection rates between malaria and arboviruses. This actually is something that we are very interested in, but I did not show any data here in the talk. If you are familiar with asymptomatic malaria infection – it’s a problem that is mostly being ignored. We did some research in Mozambique, back in 2005, where we went to our primary schools in areas of high transmission for malaria. We took blood samples from the children – otherwise healthy looking children – and we tested for malaria not using rapid tests, but by using blood smear. We found that 55% of the children showed parasitemia in the blood and then there were some with high parasitemia in their blood. So coming back to your question of coinfection: People that have immunity against malaria, because of the continous exposure, can have parasitemia and not be sick. Imagine now if they got fever and they go to the hospital. The hospital will test first for malaria and 55% of the children that go to the hospital will be positive but mainly have other causes of fever. So that means that they will never be picked for other possible infections. It is not bad that the patients are treated for malaria because of their parasitemia, because at some point they can develop malaria or they can transmit. But other diseases would be ignored and arbovirus problems will expand. It is amazing that in several parts of Mozambique where we have carried our vector survellence studies, the population of Aedes is high, but the control is based on Anopheles. So arborviral diseases are ignored and have been ignored for very long because of these reasons.

• Félix Rey: Is there any interference between the circulating parasites and arboviruses? Nobody knows?

• Eduardo Samo Gudo: That’s right, nobody knows.