Rift Valley fever

Rift Valley fever (RVF) is a vector-borne viral disease that can cause severe illness in domestic animals and poses a significant zoonotic threat. The disease is named after the geographical area where it was first discovered in 1931. 
RVF is primarily spread by multiple mosquito species that can transmit the virus from infected animals to other animals and humans. Some mosquito species can pass the virus vertically (from adult to eggs), allowing the virus to survive in the environment for years under dry conditions. During periods of high rainfall or flooding, the eggs can readily hatch and transmit RVF virus to susceptible hosts, leading to an increase in animal and human infections. 

RVF can affect both domestic and wild ruminants. Clinical signs of RVF can vary in severity depending on the species and age of the infected animal and on whether the animal is pregnant or not. They include fever, listlessness, loss of appetite (anorexia), disinclination to move, and abortions. 

Infection in young animals (lambs, goats kids, calves, and camelids) is often the most lethal, with case fatality rates of 70-100%. Adult sheep and cattle are highly susceptible to severe disease, withcase fatality rates of 20-70%. Other animal species such as camels, goats, African buffalo, domestic buffalo, and Asian monkeys are moderately susceptible (with case fatality rates below 10%). Other species can be infected but do not show clinical signs. Pregnant sheep and cattle affected by RVF almost always abort (80-100%). Humans are infected at a different degree of severity. The impacts on the health of animals translate into serious economic losses for farmers. 

Most human RVF virus infections result from direct or indirect contact with the blood or tissues of infected animals. People at highest risk of infection include herders, farmers, slaughterhouse workers, and the veterinary workforce as the virus can be transmitted to humans through the handling infected animal tissue during slaughtering or butchering, assisting with animal births, conducting veterinary procedures, or from the disposal of carcasses or foetuses.  

In these cases, humans are infected by direct inoculation (i.e. via a wound from a virus contaminated knife, direct contact between infected blood or tissues and broken skin, or the inhalation of aerosols produced during the slaughter of infected animals). RVF virus may also be present in unpasteurised milk from infected animals. Humans have also been infected with RVF virus through the bites of infected mosquitoes.  

To date, there has been no evidence of direct human-to-human transmission of RVF virus and no transmission to health care workers has been reported when standard infection control precautions have been put in place. 

Rift Valley fever is a disease for which early detection in animals and early action can reduce human health risk. In fact, animal cases precede human cases. However, in practice, the disease is often detected in humans before it is detected in animals, because surveillance in humans is usually more sensitive. If it is detected in animals early, it can be better controlled and public health measures (including risk communication and protection of high-risk individuals with personal protective equipment, vector control, reduction of animal movements (see WHO guidance)) can be put in place to prevent or reduce the risk of RVF virus transmission to humans. This reduces human infections and saves lives. Therefore, early surveillance and detection of RVF are vital to reducing public health risks. 

Yes they can. Rift Valley fever outbreaks are usually limited to specific eco-regions where livestock, humans and RVF competent vectors are abundant at the same time. They often occur after heavy rains (wetter than normal conditions).  
Models that combine earth observation data, satellite data, and ground-based surveillance can help predict outbreaks. Such predictions is essential as it enables early implementation of surveillance and preventive measures, including vaccination. 
However, models are supportive tools and are not perfect. They do need to be trained with data from the ground, and their ability to predict outbreaks varies depending on the specific region.  
The Food and Agriculture Organization of the United Nations (FAO) and NASA have been using collaborative modeling to predict RVF risk in East Africa. 
The PROVNA project (“Defining Ecoregions and Prototyping on Earth Observation (EO)-based Vector-borne Disease Surveillance System for North Africa”), a WOAH initiative, aims to help countries in North Africa target their surveillance on RVF, by tapping into remote sensing and earth observation data. 

Yes, there are several types of vaccines for animals that can reduce mortality and help to prevent an outbreak’s spread. Both live attenuated and inactivated vaccines exist for animals. Live attenuated vaccines, whilst effective and providing a long duration of immunity, may have some side effects, such as causing abortions or foetal abnormalities when given to pregnant animals. Vaccines work best if administered before an outbreak, but it can be difficult to persuade livestock owners to have their animals vaccinated with a vaccine that may have side effects when there is no outbreak. Researchers are currently trying to develop more efficacious vaccines that are safer for animals. 

There are several types of vaccines currently in development for humans, some of them are in phase II clinical trials but none have yet been licensed. 

Targeted vaccination, accompanied by surveillance – especially when performed early – remains the primary option for RVF prevention in animals in endemic areas, however care must be taken when vaccinating during an outbreak to avoid iatrogenic spread of the virus and to minimise side effects (e.g., lives vaccines are not recommended for use in pregnant animals). Vaccine campaigns conducted during an outbreak must ensure good infection control practices so to avoid iatrogenic spread of the virus and minimise side effects. 
The crucial elements for prevention and control of RVF, in addition to vaccination, are:  
– Coordination between sectors, including the sharing of information between animal health and public health services 
– Systematic, ongoing surveillance in sentinel animals to monitor RVF virus infections in susceptible animals  
– Immediate notification of clinical cases upon detection of RVF 
– Controlling the mosquito population through spraying and management of mosquito breeding grounds especially during flooding when possible 
– Effective risk communication to prevent high risk workers from being exposed to the virus 
– Public education, livestock quarantine, animal movement restrictions, and slaughter bans during the pre-outbreak and outbreak phases 

Yes, the spread of RVF is influenced by climate change. Being a vector-borne disease, its prevalence is higher in specific ecoregions that favour the presence of vectors. Climate change can modify the distribution and density of these vectors within those regions. 
Because vectors need water to reproduce, human-made structures such as dams can also influence to RVF dynamics. 

Depending on the areas where they occur, RVF outbreaks tend to occur in cycles every 7-11 years. Animals exposed to the infection during an outbreak or vaccinated, develop immunity; however, this immunity decreases over time. In addition, new susceptible animals are continually introduced into the population through births or movement. This creates a challenging situation: during major outbreaks, there is an increased attention, investment, and action covering improved surveillance and preparedness. Unfortunately, over time, with the decrease in number of cases, both interest and funding tend to decrease, until the next outbreak occurs. 

In areas where the disease is known to occur, RVF may be suspected based on clinical signs, insect activity, concurrent disease in animals and humans, rapid spread of the disease and concurrent contributing environmental factors. Laboratory tests are required to confirm RVF virus infections (WOAH Manual of Diagnostic Tests and Vaccines for Terrestrial Animals). Current diagnostic methods include molecular assays such as RT-PCR for detecting viral RNA, serological tests (ELISA, virus neutralisation) for identifying antibodies or antigens, and virus isolation in cell culture. Because RVF virus is a Risk Group 3 pathogen, diagnostic work involving live virus must be performed under biosafety level 3 (BSL-3) containment.