Uganda, "birthplace" of the Zika virus, remains free from outbreak

On the edge of a thick forest, a cool breeze blowing from nearby Lake Victoria, sits a scientific research station that looks long abandoned, its makeshift buildings in need of repair.

A mobile wheelhouse that once served as a field laboratory now has flat tyres. A steel mast used for measuring how high mosquitoes fly towers above the buildings.

"This ... place has been neglected for long, but because of the Zika virus, it is now regaining attention," said Gerald Mukisa, caretaker of Zika Forest, where the research station is located, near the city of Entebbe in Uganda.

It is here that Scottish entomologist Alexander Haddow first isolated the Zika virus – now regarded as an international health emergency by the World Health Organization – in 1947.

Haddow headed the Yellow Fever Research Institute – later renamed Uganda Virus Research Institute (UVRI) – which had been set up with funding from the Rockefeller Foundation to research yellow fever. The disease was killing many people in Africa at the time, Julius Lutwama explained.

The senior virologist works at UVRI laboratories in Entebbe, not far from the old research station in the forest.

Haddow's team was testing blood samples from monkeys that had been bitten by mosquitoes when it discovered a new virus. But even though the Zika virus was first identified in Uganda, it is believed to have existed elsewhere in Africa and in Asia as well, according to Lutwama.

The virus, spread by mosquitoes and sexual contact, has now been found to cause microcephaly, a condition in which infants are born with abnormally small heads and which is linked with the development of intellectual disabilities.

About 6,500 babies with abnormally small heads have been reported in north-east Brazil alone, the centre of the outbreak. More than 850 cases have been confirmed.

In addition to microcephaly in newborns, the virus has been linked to inflammation of the spinal cord and brain tissue, as well as impaired hearing and sight.

In adults, the Zika virus is believed to cause the Guillain-Barre syndrome, a neurological disorder that can lead to paralysis.

But while concern is growing about the Zika virus in the Americas, Asia and the Pacific, no cases are being recorded in Uganda, where few doctors are knowledgeable about it.

The first human infected with the virus was not found until 1952, in Tanzania, Lutwama said. In the 1960s, it was found in humans in Nigeria and in the Ugandan village of Ssisa, south of Zika Forest.

The virus did not cause alarm at the time. "The people ... got mild illnesses. ... They felt feverish, weak, had joint pains and some flu. In seven to 10 days, these symptoms disappeared and they never got sick again," Lutwama said.

In Ssisa, where about 14 people were diagnosed with the virus at the time, none of the infected or their relatives could be traced.

"We really have not heard about that disease. That was long ago," said Mackson Ssekiwala, a 40-year-old resident.

"I only know about the disease from the internet," forest caretaker Mukisa said.

Uganda is home to Aedes africanus, the mosquito first found to transmit the Zika virus, as well as Aedes aegypti, the species responsible for spreading the virus in Brazil.

Ugandan researchers attribute the country's lack of Zika cases to the mosquitoes' feeding habits and the apparent immunity of local people.

"In Uganda, the Aedes africanus mosquito is largely confined to the forest, rarely gets out of there, and bites at night. It feeds on monkeys and other animals" rather than humans, said Louis Mukwaya, an entomologist with UVRI.

Zika outbreaks possibly linked to microcephaly in babies have not been reported in Africa, with the exception of the Cape Verde Islands.

African populations may have developed antibodies against Zika during epidemics of yellow fever, dengue fever and other viruses within the Flaviviridae family, which Zika belongs to, Lutwama said.

Ugandan researchers say the strain spreading in Brazil originated in Asia and may have mutated after having been introduced to South America.

"We have a theory that the virus in Brazil multiplies faster in humans than ... in other parts, like Uganda," Lutwama said.

If a mosquito bites a person infected with the Zika virus in Uganda, "there would not be enough virus for the mosquitoes to pick up to be able to transmit it to another person."

There is, however, concern that the South American strain of the Zika virus could spread to Africa.

"People travel from one place to another and they may spread it. Other means are through blood transfusion. The risk is there," Lutwama said.

The risk could increase if forests are cut down, because it would make mosquitoes likelier to bite humans, he added.

Last update: Tue, 10/05/2016 - 14:15

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