A new study on Rift Valley fever in Kenya is pointing a finger at wildlife species such as African buffalo, black rhino, lesser kudu, and impala as the likely reservoir of this haemorrhage causing virus.

If the findings are proved to be true, then this research is going to demolish the widely held believe that only mosquitoes are reservoirs of the virus.

It will also provide new knowledge and approaches to management of the disease such as vaccinating wild animals and developing a human vaccine against the virus. At present, only a vaccine for animals is in existence.

The scientists behind the study believe that wild animals such as the buffalo maybe possessing the ability to coexist with the Rift Valley Fever Virus (RVFV) virus once infected, thus acting as reservoirs.

“What we found provides evidence that wild ruminants are infected by RVFV and the virus is likely to survive at very low levels inside the animal,” says Dr Kariuki Njenga, laboratory director at Centre of Disease Control, which is nested within the Kenya Medical Research Institute.

The scientists observed high prevalence of greater than 15 percent in black rhinos, lesser kudu, Thomson’s gazelle, impala, buffalo and waterbuck. Interestingly, these animals could maintain the virus at low levels without showing any symptoms of the disease.

Similarly, there are no reports that show severe disease, haemorrhage, deaths, or abortion cases in wild animals compared to those recorded in livestock whenever there is an outbreak of RVF.

According to Dr Njenga’s study, 896 serum specimens from 16 different wildlife species were collected from 19 districts across six of the eight Kenya’s provinces. Animals included in the study were African buffalo, black rhino, lesser kudu, impala, elephant, and giraffe, among many others.

After analysis of blood samples collected from these animals, some of them had detectable neutralizing antibodies against Rift Valley Fever virus. Animals that registered high levels of antibodies against the virus were: Thomson’s gazelle (87.5%), Impala (62.5 %), lesser kudu (50%), black rhino (32.6%), waterbuck (20%) and African buffalos (15.6 %).

The presence of these antibodies meant that these animals were infected by the virus and had responded by generating neutralising antibodies to fight the disease.

Even though they developed a protective mechanism, the researchers believe the virus might still be able to exist at low levels that would not result in disease development.

“The presence of neutralising antibodies in wildlife does not preclude these animals species from being reserviours of Rift Valley Fever Virus in a sylvatic cycle,” say scientists who did the study.

In Ijara district in North Eastern, 71.4 percent of the buffalos showed positive for neutralizing antibodies; 50 percent in Nakuru district; 37.5 percent in Nairobi and Laikipia districts; and 22.6 percent in Tana River districts, among others.

“One interesting thing about these figures is the two districts with the highest prevalence rates were not reported to be heavily affected in the rift valley fever outbreaks of 1997-1998 and 2006-2007, which affected humans and livestock,” says Dr Njenga.

Scientists are now recommending further studies to determine whether wild animals play a role in either virus maintenance between these outbreaks and virus amplification prior to a noticeable outbreak of Rift Valley Fever.

At the moment, this study is going to add to what scientists have been grappling with for many years: if wildlife can be infected with the Rift valley virus and if they act as reserviours.

Previous research had given conflicting reports on this relationship with a study on 281 black and white rhinos taken from Kenya, Namibia and South Africa between 1987 and 1997 showing lack of infections in wild animals.

Yet, another study in Zimbabwe suggested high levels of RVFV antibodies in black and white rhino, buffalo and waterbuck, proving the possibility of infection.

Scientists involved in the Kenyan study are upbeat with what they have found; it proves that wild animals are too infected with the virus.

They say identifying wildlife host and the vectors that maybe involved in Rift valley fever virus maintenance during an inter-epidemic period (when there are no outbreaks) could provide valuable information for the development of an effective surveillance and early warning system for potential outbreaks in humans and livestocks.

Another important finding about these wild animals failure to get sick or suffer abortions when infected as is the case with livestock is likely to push scientists to explore the possibilities of using the knowledge to develop an anti-Rift Valley Fever vaccine for humans.

Likewise, these findings may in future require the veterinary department to vaccinate not only livestock, but also wildlife within areas where there is an outbreak of Rift valley fever.

The findings further imply that during any outbreaks, wildlife meat from infected animals being sold in some restaurants may have to be tested to ensure the virus is not transmitted to human beings.

Rift valley fever is caused by a virus of the genus phlebovirus, which causes abortion and prenatal death in livestock and mild febrile sickness or sometimes death in human beings.

In animals, mortality among adult livestock is about 30 percent, while in young animals is up to 100 percent. Abortion cases are up to 100 percent in pregnant sheep, goat and cattle.

Epidemics always occur during seasons of heavy rainfall or flooding since the vector that carries the virus breeds in such environments. During the 1997-1998 El-Nino rains, more than 50,000 people were affected in Kenya, with over 400 of them dying.

In the recent Kenyan epidemic that happened between 2006 and 2007, close to 150 people died, with another over 600 reported human cases. Ijara district reported 131 cases and 27 deaths, while Garissa deaths stood at 59, with 176 reported cases in the 2006-2007 outbreak.

During the inactive period, the virus is maintained in the infected eggs of the mosquitoes belonging to the species Aedes. And when there are heavy rains, these eggs hatch into mosquitoes that are already infected with Rift valley fever virus.

The adult Aedes mosquitoes then transmit the virus to domestic animals, which replicate the viruses to high concentrations, making it readily available to Culex and other mosquito species for transmission to human beings and more animals.

The virus is also transmitted through bodily fluids when someone comes into conduct with an infected animal or person.

In another related research, Dr Njenga and other scientists have found use of portable diagnostic machines could significantly reduce the number of deaths whenever there is an outbreak of Rift Valley Fever.

Using a handy machine, quantitative real-time reverse transcriptase polymerase chain reaction (qRT-PCR), the scientists were able to determine the viral load of the people affected by Rift valley fever earlier enough than when other tests like ELISA are applied.

The test results were collected within three hours from the time the patient arrived at a health facility.

This was important as patients who were found to have a 4-fold viral load had a high death rate compared to those who survived the disease. Yet, they would have been saved if there load was known early enough to guide how such patients were to be managed.

Use of aggressive supportive therapy and antiviral drugs like ribavirin, could have been a viable option in such cases, the scientists say.

Although indicated for treatment of influenza’s and haemorrhagic fevers like Rift Valley, the antiviral drug, ribavirin, is not mostly preferred due to its adverse side-effects like liver toxicity.

Its high cost, side-effects and unproven efficacy in treatment of RVF cases, are other factors that make it less preferred in the treatment of the disease.

But researchers behind this study now recommend the use of the drug in cases identified as having high viral load and likely to turn fatal as the benefits will outweigh the costs associated with side-effects and price. 

“The findings suggest that estimates of Rift Valley Fever viral load may identify patients at risk for severe outcome, enabling them to be targeted for special or intensive clinical management,” say Dr Njenga et al. 

Unlike the other tests used, the ability of qRT-PCR to detect patients with Rift Valley fever was equally high than using the IgM antibody assay technique or ELISA, which usually used by hospitals whenever there is an outbreak.

For instance, during this study, the qRT-PCR detected RVF virus in two-thirds of the cases when the IgM machine did the same to slightly over a half of the samples. 

Another study involving 61 cases showed qRT-PCR test alone to be more sensitive than the ELISA, detecting as twice as many positive cases compared to the latter.

Dr Njenga argues that the beauty of this equipment is it ability to be used in difficult locations.

However, the use of the machine must be done in highly contained area to ensure the staff or surrounding environment is not endangered. The researchers had to undertake extreme safety measures as those used in biosafety level 4 laboratory when doing their study to ensure this does not happen.