Rift Valley fever – Mauritania

Between 30 August and 17 October 2022, a total of 47 confirmed cases of Rift Valley fever (RVF), mostly among animal breeders, including 23 deaths, have been reported from nine of Mauritania’s 15 wilayas (regions). Circulation of the virus that causes RVF in animals (small ruminants, camels and cattle) has been confirmed in eight wilayas of Mauritania. Altogether, 12 wilayas have reported confirmed human or animal cases, including nine that share borders with three neighboring countries—Mali, Senegal and Algeria. A One Health approach is being used to manage the epidemic response.

There has been a constant circulation of RVF virus in Mauritania with the country experiencing previous outbreaks in 1987, 2010, 2012, 2015 and 2020. Regional spread of the outbreak cannot be ruled out given the proliferation of the vector in the majority of wilayas, the animal density, and high human population and animal movement to neighboring countries.

Description of the outbreak

On 30 August 2022, the Ministry of Health (MoH) of Mauritania notified WHO of an outbreak of Rift Valley fever (RVF) following laboratory confirmation of a case by polymerase chain reaction (PCR) at the National Institute for Public Health Research on 29 August. The case was a 25-year-old male who was an animal breeder from Tintane moughataa (also known as district), Hodh El Gharbi wilaya (also known as region). He initially presented to a health center on 25 August with hemorrhagic syndrome (epistaxis) with severe thrombocytopenia and was transferred the following day to a regional hospital, where he died two days later on 29 August.

As of 17 October 2022, a total of 47 confirmed cases including 23 deaths (CFR 49%)—mostly among animal breeders— have been reported from nine of Mauritania’s 15 wilayas (Figure 1, Table 1). Among the 47 confirmed cases, there are more men than women (sex ratio of M:F cases = 4.4:1). The median age of the cases is 22 years, ranging from 3 to 70 years. Among the 23 deaths, nearly all occurred in hospitals and had symptoms that included severe thrombocytopenia and fever associated with the hemorrhagic syndrome (petechiae, hematemesis, gingivorrhagia).

Figure 1. Geographical distribution of confirmed human cases of Rift Valley fever (n=47) and deaths (n=23) from nine affected wilayas in Mauritania, 30 August – 17 October 2022. 
Table 1. Number of confirmed human Rift Valley fever cases and deaths, per the nine affected wilayas, Mauritania, 30 August – 17 October 2022.

Figure 2. Confirmed cases (n=47) and deaths (n=23) of Rift Valley fever by confirmation date, Mauritania, 30 August to 17 October 2022. 

Animal cases of Rift Valley fever

While human cases of RVF have been reported in nine wilayas as of 17 October 2022, confirmed and suspected animal cases have been reported in 12 wilayas (eight confirmed; four suspected) (Table 2).

An alert of potential animal RVF cases resulted from sentinel herd monitoring which notified animal deaths and abortions in Aioun moughataa, Hodh El Gharbi wilaya. The outbreak of RVF in animal populations was subsequently identified in Hodh El Gharbi and additional seven wilayas: Adrar, Assaba, Guidimakha, Hodh Echargui, Tagant, Tiris Zemmour, and Trarza. Between 18 August and 10 October 2022, a total of 1148 samples of animal origin—cattle, camel and small ruminants—were analyzed. Overall positivity was 24.1% (277/1148). Test positivity by animal group: 5.2% (5/96) were positive by ELISA IgM in cattle; 25.8% (113/438) were positive by RT-PCR in camels; 25.9% (159/614) were positive by ELISA IgM in small ruminants.

Table 2. Number of animals (cattle, camels and small ruminants) tested for RVF and results, by the 12 wilayas with reported cases, Mauritania, 18 August to 10 October 2022. 

Epidemiology of Rift Valley fever

RVF is a viral disease most commonly seen in domesticated animals in sub-Saharan Africa, such as cattle, sheep, goats and camels. RVF primarily affects animals but also has the capacity to infect humans.

While some human infections have resulted from the bite of infected mosquitoes, most human infections result from contact with the blood or organs of infected animals. Occupational groups such as herders, farmers, slaughterhouse workers and veterinarians are at higher risk of infection.

Humans may also become infected by ingesting the unpasteurized or uncooked milk of infected animals. No human-to-human transmission of RVF has been documented.

Although RVF often causes severe illness in animals, in humans, the disease ranges from a mild flu-like illness to severe haemorrhagic fever that can be lethal. Most people with RVF have either no symptoms or a mild illness (fever, weakness, back pain, and dizziness). However, a small percentage (8-10%) of people with RVF develop severe symptoms, including eye disease, hemorrhage and encephalitis (swelling of the brain).

An outbreak of RVF occurred in Mauritania from September to November 2020, which involved 78 reported human cases and 25 deaths (CFR 32%)^[1]. A total of 186 animal cases of RVF were reported: 94 camels, 89 small ruminants and three cattle.

A One Health approach is being used to manage the epidemic response, including the establishment of a One Health technical committee for a coordinated response at the national level. In the affected wilayas, coordination meetings bringing together the human health and animal health sectors are held weekly.

The following priority activities are being implemented:

• Organization of daily meetings of the One Health technical committee for the management of this epidemic under the coordination of the Ministry of Health.
• Organization of in-depth epidemiological and entomological investigations.
• Development of regular situation reports.
• Sensitization of affected communities, in particular at-risk populations (animal breeders and butchers), on preventive measures and what to do in the event of abortions and deaths within herds, or the occurrence of a haemorrhagic syndrome in a person and active search finding.
• Supplying drugs and personal protective equipment (PPE) to health facilities in affected areas.
• Reinforcement of diagnostic and management capacities of health facilities in affected areas.
• Mobilization of partners for material and financial support resources.

RVF is not unusual in Mauritania. The country previously experienced outbreaks in 1987, 2010, 2012, 2015 and 2020. Transmission can occur through carrier mosquito bites, contact with contaminated blood or tissues, and during the slaughter of animals. Confirmation of virus circulation in animals from several areas the majority of wilayas presents a significant risk of amplifying the disease in humans.

The precarious environmental conditions, inadequate sanitation services in the affected localities, and high animal density contribute to the proliferation of vectors and the spread of the virus. The abundant rainfall recorded this year and flooding in most of these wilayas, combined with the dumping of waste tires, used containers and garbage, enhances the proliferation of vector breeding sites.

The risk of spread at the regional level is moderate. Mauritania is an agro-pastoral country, and the movement of animals in search of water and pasture increases the risk of disease spread. Recurrent cross-border pastoral movements increase the risk of regional spread of the disease into neighboring countries. Fourteen of Mauritania’s 15 wilayas have reported either confirmed human, confirmed animal or suspected animal cases^[2], of which nine border Mali, Senegal or Algeria; specifically, the wilayas of Assaba, Adrar, Hodh El Chargui, Hodh El Gharbi, Guidimakha and Tiris Zemmour border Mali; the wilayas of Brakna, Gorgal, Guidimakha and Trarza border Senegal, and the wilaya of Tiris Zemmour borders Algeria. Moreover, RVF is not among the diseases subject to vaccination control of cattle at the borders; and transhumance— a practice characterized by pastoralism and movement of livestock under the care of herders —is frequent within Mauritania and across the borders into Mali and Senegal. Livestock markets in some countries in the sub-region are supplied from Mauritania.

The global risk is estimated to be low.

Rift Valley fever (RVF) is a zoonosis that mainly affects domestic animals, in particular cattle, sheep, camels and goats. Human cases often occur close to outbreaks in livestock, in an environment conducive for local transmission of the virus by mosquito vectors. Most human infections result from direct or indirect contact with the blood or organs of infected animals. Precautions should be taken when in contact with sick animals or patients, as well as with their products and laboratory samples. No human-to-human transmission of RVF has been documented.

Public health messaging. Information campaigns on the risk factors for RVF transmission as well as protective measures, such as vector control and protection against mosquito bites, are essential to reducing the number of infections and deaths among people. Public health messages aimed at reducing risk should focus on the following:

• Reduce the risk of animal-to-human transmission through safer animal husbandry and slaughter practices, including practicing hand hygiene, wearing gloves and other appropriate PPE when handling sick animals or their tissues, or when animals are slaughtered.
• Reduce the risk of animal-to-human transmission from unsafe consumption of fresh blood, raw milk, or animal tissues. In epizootic regions, all animal products (blood, meat, and milk) must be carefully cooked before being consumed.
• Implementation of vector control activities (e.g. elimination of larvae in breeding sites), and use of insecticide-treated bed nets and repellents.
• Wear light-coloured clothing (long-sleeved shirts and pants) and avoid outdoor activities during times when the vector species is most frequently active/biting.
• Restrict or prohibit the movement of livestock to reduce the spread of the virus from infected to uninfected areas.

Animal vaccination. When implemented before an outbreak, routine animal vaccination can prevent RVF epizootics. Vaccination campaigns are not recommended during an epizootic because this represents a risk to generate virulent reassortments. As RVF epizootics in animals precede human cases, the establishment of an active animal health surveillance system is essential to provide early warning to veterinary and human public health authorities.

Healthcare workers. Although no human-to-human transmission of RVF has been observed, there is a theoretical risk of transmission of the virus to healthcare personnel through contact with contaminated blood or tissue from infected patients. Thus, healthcare workers confronted with suspected or confirmed cases of RVF should apply standard precautions when handling specimens from their patients.

WHO advises against the application of any travel or trade restrictions to Mauritania or the affected regions, based on information currently available on this event.

• World Health Organization, Rift Valley Fever: https://www.who.int/health-topics/rift-valley-fever#tab=tab_1
• World Organization for Animal Health, Rift Valley Fever : https://www.woah.org/en/disease/rift-valley-fever/
• WHO fact sheet, Rift Valley fever:  https://www.who.int/fr/news-room/fact-sheets/detail/rift-valley-fever
• Disease Outbreak News, Rift Valley fever in Mauritania, published on 13 November 2020: https://www.who.int/emergencies/disease-outbreak-news/item/rift-valley-fever-mauritania

^[2] Fourteen wilayas have reported either confirmed human, confirmed animal or suspected animal cases. Twelve wilayas reported both confirmed human and animal cases, while two wilayas have reported suspected animal cases only (Tiris Zemmour and Trarza). Nine wilayas reported confirmed human cases (Adrar, Assaba, Dakhlet Nouadhibou, Hodh Echargui, Hodh El Gharbi, Nouakchott Nord, Nouakchott Oest, Nouakchott Sud and Tagant), eight reported confirmed animal cases (Adrar, Assaba, Guidimakha, Hodh Echargui, Hodh El Gharbi, Tagant, Tiris Zemmour and Trarza). Among these, five wilayas overlap in reporting both confirmed human and confirmed animal cases.

Citable reference: World Health Organization (20 October 2022). Disease Outbreak News; Rift Valley fever – Mauritania. Available at: https://www.who.int/emergencies/disease-outbreak-news/item/2022-DON417