Tag: Zika

Did African travellers introduce the zika virus to Brazil?

Researched by Sarah Wild

In Brazil, 404 babies were born with microcephaly in 2015 – a disorder in which a foetus’s brain does not develop properly in the womb — with thousands more cases under investigation.

Of those, 17 babies were infected with the zika virus, a mosquito-borne disease, and 76 have died. Due to these developments, the World Health Organisation declared the zika outbreak a “public health emergency of international concern” earlier this month.

Health authorities are investigating whether zika, which was first discovered in Uganda, is behind the rise in microcephaly, and fingers have been pointed at African tourists for bringing the virus to Brazil. NPR reported earlier this month that “some doctors speculate it could have come with African visitors during the [2014 Football] World Cup”.

Two doctors from the Saõ Paulo Institute for Tropical Medicine wrote that is was the “strongest hypothesis” for the outbreak of zika in Brazil.

Other media reports (from The Guardian, Reuters, and Mail & Guardian) ascribed blame to either a visitor from Africa or Oceania.

 

Why were Africans under suspicion?

The reports contain no sources for the statement and there is no mention of it on the Brazilian government’s official website or the ministry of health’s.

The Brazilian health authorities have not responded to numerous inquiries from Africa Check about whether they initially blamed African tourists for the zika outbreak, and whether they still do.

The closest that Africa Check could find was a statement by Brazilian president Dilma Rousseff: “The zika virus, transmitted by mosquito, has no nationality. It began in Africa, spread throughout Southeast Asia, the Oceania and is now in Latin America. And this was an exceptionally fast process, from last year.” (Note: This was translated using Google Translate, so excuse our Portuguese.)

 

First zika cases recorded in the 1950s

In reality, the migration of the zika virus from Africa to Brazil has taken decades, and it went the long way round, scientific literature shows.

The virus was first isolated in a rhesus monkey in Uganda’s Zika forest in 1947 while scientists were studying yellow fever. In 1952, a paper was published describing the disease in humans in Uganda and Tanzania.

Zika is a flavivirus, which is a family of viruses that are usually carried by ticks and mosquitoes, and is closely related to other diseases such as dengue, yellow fever and Japanese encephalitis (a viral inflammation of the brain).

Between 1952 through to 1981, zika infections were reported in numerous African countries, and then later in parts of Asia, including India, Malaysia, the Philippines, Thailand, Vietnam and Indonesia.

 

From Africa and Asia to Oceania

Until 2007 no one had been diagnosed with the virus outside of its endemic areas in Africa and Asia.

In that year, an outbreak was detected on Yap Island in Micronesia (which infected almost 75% of the population), which then spread to French Polynesia in 2013 and 2014 and a number of other Pacific islands.

Aedes mosquitoes — a genus of mosquito found all over the world — are considered the main carrier of the disease, as are other infected people. When mosquitoes bite a human who has the virus, they become infected too and transmit it to the next person they feed on. There have also been reported cases of zika being transmitted through sexual intercourse.

 

Different strains of zika virus

By analysing the evolutionary development of the zika virus, scientists believe that zika spread from Africa to Asia and not the other way around, Dr Petrus van Vuren from South Africa’s National Institute of Communicable Diseases told Africa Check.

“It is, however, not impossible that the virus might have been present in Asia long before it was detected eventually,” he said.

Because of this, three different genotypes, or collections of genes, of the zika virus developed: the African (east and west) and the Asian, Dr Anna-Belle Failloux, head of arboviruses and insect vectors at the Institut Pasteur in Paris, told Africa Check.

DNA tests showed that the zika virus that has struck Brazil is the Asian strain. The Centers for Disease Control and Prevention in the US told Africa Check that this made it unlikely that it came from an African country.

“The strain of zika virus detected in Brazil was most closely related to the Asian strain that had been circulating in French Polynesia,” they said.

 

How did the zika virus get to South America?

In a communique on the zika virus, the National Institute for Communicable Diseases says: “One could speculate that numerous introductions of either infected mosquitoes or infected travellers are necessary before a foreign arbovirus can become established in a new area, because the virus needs to be introduced into a capable vector population as well as host population.”

Asked how the virus could have arrived in Brazil, Failloux told Africa Check that it was more likely that it was brought by an infected traveller: “We cannot completely exclude an infected mosquito taking the plane [… but the] main and more realistic way to transfer the virus from one continent to another is through infected people.” The virus also causes no symptoms in 80% of cases, she said.

However, no countries from zika-virus-endemic Pacific countries competed in the 2014 Football World Cup, Didier Musso from the Institut Louis Malardé in Tahiti, French Polynesia, noted in a journal article.

Shortly thereafter though teams from the Pacific regions of French Polynesia, New Caledonia, Cook Islands and Easter Island – where the zika virus circulated in 2014 – competed in an international canoe sprint competition in Rio de Janeiro, Musso pointed out.

But even this is not a direct link to the current zika outbreak because it is possible that zika arrived in Brazil before that.

The first zika case in Brazil was confirmed with a laboratory test in May 2015, but “there were reports of ‘dengue-like syndrome’ occurring before this time,” the Centers for Disease Control and Prevention told Africa Check.

“It is more likely that the virus was already circulating and causing illness prior to May 2015, but had not been recognised as zika until later.”

 

Conclusion: Highly unlikely that an African traveller introduced zika to Brazil

Although the zika virus was first detected in Africa, three distinct strains of the virus now exist: the west and east African, and Asian. The Asian strain has been confirmed as the cause of Brazil’s zika cases.

It is possible that the virus was brought by an infected traveller – possibly from Oceania which had the first documented cases of zika outside of its endemic areas in Africa and Asia – during a sporting event, whether it was the 2014 Football World Cup or an international canoe sprint competition shortly thereafter.

It is, however, possible that the virus was present in Brazil before these events, and was misdiagnosed.

 

Additional reading

World Health Organisation: Microcephaly/Zika virus

Zika virus disease timeline

 

First published on Africa Check.

Do African countries have to worry about a zika resurgence?

Researched by Sarah Wild

The zika virus, which has been associated with cases of microcephaly in Brazil and nervous system disorders in Micronesia, was originally discovered in Africa in 1947.

“For 60 years, [zika] was seen as a mosquito-spread virus causing mild illness occasionally in African populations across the equatorial belt,” Prof Jimmy Whitworth, with the London School of Hygiene and Tropical Medicine, told Africa Check.

(Someone infected with zika may have a fever, rashes, conjunctivitis, muscle and joint pain and headaches, the World Health Organisation explains.)

Since it was neither fatal nor disfiguring, the virus has only recently come into the spotlight, following its association with brain growth disorders in Brazilian babies whose mothers were infected while pregnant. This causal link, however, has not been proven.

 

‘Virus appears to have changed in past decade’

Between 1952 through to 1981, zika infections were reported in numerous African countries, and then later in parts of Asia. In 2007, outbreaks were reported in Micronesia, and subsequently South America. Last year cases were detected in Cape Verde, the island nation off the coast of West Africa.

Because of its migration around the world, three different strains of the zika virus developed: the African (east and west) and the Asian.

The strain detected in Brazil was the Asian virus. The World Health Organisation (WHO) was unable to tell Africa Check whether Cape Verde’s zika was the Asian strain, but no neurological disorders have so far been reported in foetuses there.

It is unknown how the various zika strains differ, the WHO said. But the virus appears to have changed in the past decade, given the speed at which it has moved to new locations, Whitworth told Africa Check.

He said that its severity could be due to people lacking immunity to it in the new location, changes in the virus that could make it easier for mosquitoes to transmit it, or the possibility of previously missed infections in African countries where zika is not commonly found.

 

Do Africans in zika areas already have immunity?

African populations in areas where zika is prevalent will probably have some immunity to the virus, especially in countries which have had infections previously, Whitworth said.

“It might be there is enough immune protection [within African populations] to prevent an epidemic occurring in Africa, but we do not know that yet,” he said.

The WHO said that researchers have found some people in Africa who show traces of the antibodies that once fought off the zika virus, but they do not know whether these antibodies would protect them against a reinfection with a different strain of the virus.

A virology expert and fellow of the Academy of Science of Nigeria, Prof Oyewale Tomori, told Africa Check that it was difficult to say whether the Asian zika strain could reinfect African populations.

“Given the numerous other viruses related to zika in Africa — West Nile, Yellow Fever, Wesselsbron, and others — the reinfection in Africa may be as mild as previously reported in the 1940s and 1950s,” he said. “Note that zika is not the only virus that was originally isolated in Africa, causing mild infection, and had gone on to cause more severe infection in other parts of the world.”

Tomori was speaking of the West Nile virus and Chikungunya, also transmitted by mosquitoes. In 2012, a West Nile outbreak in the United States claimed 286 lives. A global outbreak of Chikungunya in 2013 resulted in 191 reported deaths.

 

No cases south of Uganda

Aedes mosquitoes, which are found all over the world, are considered the main carrier of the disease, as are infected people.

In Africa, these mosquitoes are found as far south as South Africa, but no case of locally-acquired zika has been reported in humans south of Uganda, South Africa’s National Institute of Communicable Diseases (NICD) said in a communique about the zika virus.

A number of elements have to be present for zika to move south: the virus needs to be introduced into a susceptible mosquito population as well as the human population.

The NICD said that its local “typical African subspecies tends not to bite humans and may well be less susceptible to zika virus when compared to the South American ones”.

While an infected traveller could introduce zika to Southern Africa, the short time that the virus is present in the blood means it is unlikely that the local Aedes mosquitoes will be very successful carriers, as they have a very limited flight range, measured in meters, and tend not to enter buildings, the NICD said.

Because of this zika is not giving him sleepless nights, South Africa’s health minister, Aaron Motsoaledi, reportedly told parliament after a Colombian businessman was diagnosed there with the disease in February.

 

Mosquito control the best prevention

In the end, prevention is better than cure, the WHO regional director for Africa, Dr Matshidiso Moeti said: “The most effective forms of prevention are reducing mosquito populations by eliminating their potential breeding sites, and using personal protection measures to prevent mosquito bites.”

She called upon African countries to “strengthen mosquito control, surveillance and laboratory detection of zika virus disease and neurological complications, as well as public awareness”.

This sentiment was echoed by Nigeria’s Tomori, who said: “Certainly we should prepare [for a possible new zika outbreak] and this will involve mosquito control, especially Aedes mosquitoes. This may also help with reducing the occurrence of other mosquito-borne diseases.”

 

First published in Africa Check.