Rift Valley fever ‘may strike again’ soon

As fears have been growing that Rift Valley fever could hit East African countries again in early 2009, a research-based 'toolkit' is helping the Kenya Government to manage the risk to human and animal lives.

Songs of PraiseThe Government of Kenya and its partners are preparing for a Rift Valley fever outbreak if the short rains of this East African region are unseasonably heavy or prolonged in high-risk areas during December 2008 and January 2009 (FEWSNET: 11 December 2008). Livestock keepers are being urged to report unusually high numbers of animal deaths or sick animals with increased rates of abortion, low milk yields, yellowing of eyes, blood-stained nasal discharges or blood in faeces.

In September 2008, EMPRES WATCH, the newsletter of the Emergency Prevention System for Transboundary Animal and Plant Pests and Diseases, a unit of the United Nations Food and Agriculture Organization (FAO), issued a chilling warning to countries in Africa and the Arabian Peninsula that Rift Valley fever could strike again soon.

ILRI veterinary epidemiologist Christine Jost says: 'While heavy rains in northern Kenya and elsewhere generated concerns that Rift Valley fever might reappear in the rainy season (October–November 2008), there have been no outbreaks of the disease reported yet in Kenya. A reported outbreak in Saudi Arabia is being controlled.'

The last outbreak of Rift Valley fever in East Africa, in late 2006 and early 2007, killed more than 300 people in Kenya, Tanzania and Somalia and severely disrupted the local and regional livestock trade and associated livelihoods. In Kenya alone, economic losses were estimated to have exceeded US$30 million, with the country’s poorest pastoral peoples bearing the brunt of the losses.

The EMPRES warning was based on climatic models that track anomalous sea-surface temperatures in the Indian and Pacific oceans. With or without accompanying El Ñino events, these have been shown to be associated with abnormally prolonged and heavy rainfall in East Africa.

Rift Valley fever is spread initially by mosquitoes feeding on livestock; unusually heavy rainfall and subsequent widespread flooding provide ideal conditions for the generation of vast swarms of these insects. Very unusually, this year a ‘positive Indian Ocean Dipole’ has been detected for the third consecutive year. This phenomenon was associated with serious outbreaks of Rift Valley fever in East Africa in 2006/07, in Sudan in 2007 and in Madagascar in 2007/08.

Over the past 70 years or so, Rift Valley fever outbreaks in East Africa have occurred on average every 10 years; before 2006, the last outbreak had occurred in 1997/98. The apparent increase in frequency of outbreaks in the region starting in 2006 may indicate that climate change is already impacting this and other diseases associated with specific climatic conditions

What is Rift Valley fever?

Rift Valley fever is a viral disease that mostly affects cattle, sheep, goats and camels and sometimes also infects people. In arid and semi-arid part of East Africa, it is associated with abnormally heavy rainfall and flooding, which provides ideal conditions for mosquitoes to emerge and breed. Livestock bitten by mosquitoes infected with the virus that causes Rift Valley fever can themselves become infected, after which a wide range of biting insects transmit the disease further.

The females of one group of mosquitoes (Aedes) can pass the virus to their eggs, which can survive for long periods of time in the soil. When flooding occurs in an area, the eggs in the soil hatch and those carrying the virus quickly develop into adult mosquitoes already infected with virus, which then transmit the virus to livestock.

It is thought that people become infected with Rift Valley fever mostly through close contact with infected livestock: animal health workers and those involved in slaughtering and butchering infected animals are at most risk. The general public is at little risk so long as people thoroughly cook any meat they eat.

Although most human Rift Valley fever cases are mild and present as flu-like conditions, the disease can be much more severe and lead to death.

Lessons learned from the 2006/07 outbreaks
In late 2006, pastoralists in northeastern Kenya observed unusually heavy rainfall and flooding, the emergence of swarms of Aedes mosquitoes and the first cases of the livestock disease they recognized as Rift Valley fever—all before an international Rift Valley fever warning was issued. Although the pastoralists reported the situation to local authorities, the flooded roads and heavy rains, in addition to the region’s remoteness and generally poor infrastructure, made acting on the reports problematic. Many roads became impassable, for example, and much of the affected region lay outside areas with mobile phone coverage. Official action in the affected and at-risk communities was taken only with the first reports of human cases, by which time it was already too late to contain the outbreak in livestock and prevent human deaths.

  • ILRI and the Kenyan and Tanzanian veterinary departments worked together to conduct a series of studies of the 2006/07 outbreak, from which several lessons emerged.
  • A government-approved contingency plan to control outbreaks of Rift Valley fever should be in place well before a possible outbreak.
  • A system should be established to make emergency funds available at an early stage of an outbreak (before human cases occur).
  • International early warning systems should be supplemented with local systems that enable pastoralists and other people in the affected areas to report unusual weather and mosquito occurrences and suspected cases of Rift Valley fever in both animals and people. The widespread availability of mobile phones and increasing mobile phone coverage now make such an approach more feasible than in the past.
  • Existing vaccines for livestock are difficult to use effectively in East Africa because:

    • the disease occurs in remote areas with poor infrastructure
    • neither manufacturers nor veterinary authorities routinely maintain large stocks of vaccine for Rift Valley fever
    • vaccine manufacturers need several months’ warning to produce sufficient new batches of the vaccine to enable sufficient populations of at-risk animals to be vaccinated
    • the existing vaccine is not ideal; it causes abortion in pregnant animals
    • vaccinating animals after cases of Rift Valley fever have been detected in a herd risks spreading the virus further via the needle used for the vaccinations
    • the long intervals between outbreaks of Rift Valley fever make routine vaccination of large numbers of livestock against the disease appear prohibitively expensive.
  • Effective communication is vital to managing outbreaks of Rift Valley fever; all those in close contact with livestock, for example, should be informed of the risks associated with slaughtering livestock and handling carcasses. Clear, authoritative messaging is perhaps the single most important action that can be taken to prevent loss of human as well as animal life.
  • Because the disease is transmitted between livestock and people, it is essential that medical and veterinary authorities collaborate closely with each other to prevent and control outbreaks.

A decision-support tool is used for contingency planning
Once an outbreak of Rift Valley fever occurs, the disease spreads rapidly, leaving little time for authorities and affected communities to weigh options and make decisions. And due to the on-average decade-long interval between outbreaks, many of those with firsthand experience of an outbreak are no longer in their posts to tackle the next.

To address this, FAO and ILRI worked with multiple stakeholders to improve control of Rift Valley fever by developing a ‘decision-support’ tool. Targeted at directors of veterinary services in the East Africa region, the tool divides an outbreak of Rift Valley fever into a sequence of 12 key events, including the normal inter-epidemic period. For each event or period, the tool recommends a set of actions to facilitate timely, evidence-based decision-making.  The tool helps decision-makers act early for prevention and control, based on an increasing levels of outbreak risk, rather than waiting for an outbreak to occur before action is taken.

Recently, in response to the Rift Valley fever warning issued by FAO, the decision-support tool was used by the Kenyan Veterinary Department to inform the drafting of a Rift Valley fever contingency plan. 

Leave a Reply

Your email address will not be published.