It is early morning and a team of scientists are heading to the National Livestock Resources Research Institute to interact with scientists who are being visited by stakeholders including USAID who were on a fact finding

During the cause of the interaction one of the interesting technologies which the donor stakeholders were amazed of is the Insectary Laboratory were scientists have confined mosquitos spreading Rift Valley Virus in animals and humans.

Rift Valley fever is a viral disease most commonly seen in domesticated animals in sub Saharan Africa, such as cattle, buffalo, sheep, goats and camels.

Human beings can get RVF through contact with blood, body fluids or tissues of infected animals or through bites from infected mosquitoes.

In livestock, Rift Valley Fever infections are characterized by sweeping abortion storms in female animals and up to 100% mortality in calves.

Rif Valley Fever occurrences are prevalent in the animal husbandry sector in Uganda, the reason Scientists at the National Livestock Resources Research Institute (NaLRRI) Nakyesasa are conducting research studying the characteristics of the mosquitoes spreading the virus in a bid for farmers to use the right insecticides to eliminate them.

Background

Rift Valley Fever has a complex lifecycle involving humans, mosquitos, wild and domesticated animals and the environment.

The virus is transmitted from either mosquitoes or farm animals to humans but person to person transmission has not been documented.

In a 2021 publication in Journal of Environment and Health based in USA led by Doreen Birugi, Freda Loy Aceng, Dixon Denis Oipi and others about sporadic Rift Valley outbreaks in humans and Animals in Uganda from October 2017- January 2018, details are stated as below.

“The primary reservoir and vector for RVFV is the Ades mosquito though it can be transmitted by other mosquitoes such as Anopheles and Culex.  

These mosquitos can lay infected eggs that can stay in the soil for a long period in dry conditions and hatch during   wet months into infected mosquitoes.

Therefore, in flooding situations, the infected eggs can be transported to new locations hence spreading the virus to different geographical locations.

The infection can also spread due to animal movements introducing infected animals to new territories.

In the animals, transmission is mainly through bites of Aedes mosquitoes. However, the disease is mainly acquired in humans through contact with blood, body fluids, or tissue and consumption of raw or undercooked milk or meat from infected animals.

This is why persons who interact with animals such as veterinarians, herders and butchers are a high-risk population for RVF.

The virus was discovered in 1930 in the rift valley area in Kenya during an epidemic investigation on Sheep and it has caused multiple outbreaks in Africa and the Middle East.

Since it was reported then, many epidemics have occurred in various regions including Egypt in 1977, Kenya 1997–1998, Saudi Arabia 2000–2001, Yemen 2000–2001 and Kenya 2006-2007.

Historical reports of RVF in Uganda date back to 1944 when an RVF virus was first isolated from mosquitoes captured in forest in western Uganda in 1944

In East Africa, outbreaks often occur after prolonged and heavy rains and floods.

The research at NaLRRI

Dr Patrick Abila a research officer and entomologist at NaLRRI heading the research explained to the stakeholders that under a project “Mosquitos blocking boosting of Uganda’s investment in livestock development (build)” his team is studying the characteristics of two mosquito species spreading Rift Valley in animals.

This is a three year project done jointly with scientists at the International Livestock Research Institute (ILRI) based in Nairobi Kenya and Free University of Berlin in Germany.

How the virus is transmitted

Abila explains that much as Anopheles mosquitos spreads Malaria in humans, Aedes aegypti and Culex mosquitos spread Rift valley fever in animals.

The virus is spread from the mother mosquito to the laid eggs, to the larvae, pupa and back to grown mother and Aedes mosquito is a primary transmission vector.

Culex Mosquito is a secondary vector because it picks the virus from an infected animal thereby spreading it as it goes biting animals in the grazing land.

In humans in it can be transmitted in various ways including consumption of infected raw milk, beef of infected animal and infected mosquitos bites thereby causing haemorrhagic fever which may be mild and disappear or causing serious infection if not treated may lead to death depending on one’s genes.

In cattle and other animals, it causes abortion to the foetus and usually it leads to high rates of death in calves.

The disease has an incubation period of 2–6 days in humans and varies in severity; that is, some remain asymptomatic and others might experience mild illness whereas some may have severe disease.

Rift Valley fever virus patients may present with fever, generalized weakness, back pain, and dizziness which can clear within 2–7 days.

However, 8–10% can develop severe disease characterized with visual disease, encephalitis, or haemorrhagic fever.

About 50% of those that develop severe disease either die or remain with permanent disabilities.

In 2017–2018, the Uganda Ministry of Health through the Public Health Emergency Operational Centre received alerts of suspected viral haemorrhagic fever from Kiruhura, Buikwe, Kiboga, and Mityana districts.

Laboratory results from the Uganda Virus Research Institute (UVRI) indicated that human cases were positive for RVFV.

Outbreaks

Cases have been reported from districts of Kiboga, Mityana, Buikwe and Kiruhura districts in the cattle corridor of Uganda.

This is because the main economic activity carried out in these districts is livestock farming.

Certain environmental factors such as dense vegetation, temperature conditions that favour mosquito breeding and virus replication and presence of ruminants such as cattle, sheep and goats that can amplify transmission of the virus.

Areas with a flat topography, water retaining soil types and dense bush cover are important factors for flooding and mosquitoes breeding.

In 2006–2007, Kenya, Sudan, Tanzania, and Somalia experienced a major RVF outbreak involving large numbers of humans and livestock.

Uganda reported an RVF outbreak after a long interval in March 2016.

The isolate was later developed into Smithburn modified live virus vaccine. Another RVF occurrence was reported in 1968 in humans and livestock in Kabale district in south-western Uganda.

Since the Kabale case in 2016 outbreak, other sporadic cases have been experienced in different parts of the country.

Between August 2017 and August 2018, Uganda experienced frequent RVF outbreaks in the districts of Kiboga, Kyankwanzi, Kiruhura, Isingiro, Ibanda, Lyantonde, Sembabule, Mubende, Mbarara, Kasese, Sheema, Arua, Buikwe, Lwengo and Mityana.

A few cross-sectional surveys have been done in the country to estimate RVFV seroprevalence in selected areas.

A seroprevalence of 6.7% for anti-RVFV antibodies was reported among the domestic ruminant population in samples that were collected during a yellow fever outbreak investigation of 2010–2011 in the northern region.

During the 2016 outbreak in Kabale district, the seroprevalence of RVFV in southwestern Uganda was reported to be 27%, 7% and 4% and 12% in cattle, goats, sheep and humans respectively.

A survey that was conducted in goat farms in central Uganda in 2009 showed seroprevalences of anti-RVF in sheep and goats of 9.8% and 24.3%, respectively.

While the various seroprevalence studies that have been implemented have illustrated the burden and risk factors for RVF in various locations, more work is still needed to map the distribution of the disease risk across the country

Research Process

Dr Abila and his team are carrying out the research at the Mosquito Insectary Laboratory at NaLRRI. This is after they went collecting the two mosquito species in the districts of Isingiro, Nakyesasa Sembabule and Lyantonde among others.

Since most animals in these districts have been exposed to the virus, the research is to manage the mosquito population.

The scientists are keeping the mosquitos under temperature between 25-27 degrees Celsius and they are fed on born blood from the animals. It takes them ten days to lay eggs.

They have studied that most of these mosquito species resist insecticide spraying.

They are introducing specific insecticides to the mosquitos and the study the genes of those that die and those that resist.

In case of the later they introduce at least two or three types of insecticide and in case they die, then the farmer will be advised to combine insecticides for the species that resist one type of insecticide.

The good news is the mosquito species collected from various parts of the country are marked and the scientists know which one is resistant and which one is not.    This way farmers from the different regions can be advised accordingly.

The team has two years to go with the research work and thereafter they will recommend deliverable tools for intervention to Ministry of Health and Ministry of Agriculture for them to implement how to control mosquito population in the cattle corridor areas.