Rift Valley Fever – Mauritania

The Ministry of Health (MoH) informed the WHO that between September 13 and October 1, 2020, eight cases of Rift Valley Fever (RVF) were confirmed by animal breeders, including seven deaths. Included neighborhoods include Tidjikja and Moudjéria (Tagant region), Guerou (Assaba region) and Chinguetty (Adrar region). Laboratory confirmation of RVF infection was performed using a reverse transcription polymerase chain reaction (RT-PCR) at the National Institute of Public Health Research (INRSP) in Nouakchott. The age of the infected patients varied between 16 and 70 years and included one woman and seven men. All seven deaths occurred among hospitalized patients with fever and hemorrhagic syndrome (petechiae, gingivorrhagia) and vomiting.

Between September 4 and November 7, 2020, a total of 214 people were sampled and their samples were sent to the INRSP for laboratory testing, with a total of 75 positive RVF tests (RT-PCR and enzyme-linked immunosorbent assay (ELISA) serology. Positive cases recorded are in 11 of the 15 regions of the country: Brakna, Trarza, Gorgol (on the border with Senegal), Adrar, Assaba, Hodh El Gharby, Hodh El Chargui, Guidimaka (on the border with Mali) and Nouakchott Sud, Nouakchott Ouest and Tagant. the affected Tagant region (38/75, 51%) with the main focal points of Tidjikja and Moudjeria.A total of 25 deaths have been reported since this outbreak.

Animal outbreaks have also been confirmed in the regions of Assab, Tagant, Brakna, Trarza, Hodh El Gharbi and Hodh El Chargui. The results of 557 animal samples taken as of October 15, 2020, showed that 74 camels, 52 small ruminants, and 12 cattle were positive for Rift Valley fever.

Public health response

Since the outbreak, the WHO has worked closely with the Ministry of Health to respond to the current outbreak and monitor developments in the epidemiological situation.

The WHO supports the following public health activities in response to the outbreak:

• Regular coordination and technical meetings between the public and animal health sectors
• Coordination of epidemic response activities at the human-animal interface in all affected regions
• Epidemiological research
• Strengthening diagnostic capacity
• Preparation of communication tools
• Resource mobilization and expertise

Joint field missions by FAO, RES and WHO experts are planned to support the MoH and the Ministry of Rural Development in preventing and controlling RVF outbreaks, especially in terms of laboratory capacity, monitoring and risk communication for different vulnerable populations. other aspects related to the concept of “One Health”.

WHO risk assessment

The COVID-19 epidemic, which has been going on since February 2020, is putting pressure on health services and the activities of the National Reference Laboratory for Public Health (INRSP). There is a high demand for analysis of COVID-19 samples, limiting the processing of samples from other pathologies. The lifting of measures to combat the COVID-19 epidemic and restrictions on travel abroad have led to an increase in the movement of people to rural areas in search of animal products (such as milk and meat).

RVF attacks have previously been reported in Mauritania, and in the past the country has experienced six major epidemics (1987, 1998, 2003, 2010, 2012 and 2015) affecting several departments in the regions of Brakna, Tagant, Assaba. , Adrar, Inchiri, Trarza, Hodh Elgharby and Hodh El Chargui. The current epidemic affecting humans and animals occurred after heavy, unusual and prolonged rains in regions with high animal density which contributed to the spread of the vector and the spread of the virus. During the hot seasons, people spend more time in rural areas with a history of RVF transmission, resting at night outdoors. This could be a risk factor for exposure to mosquitoes and other disease vectors. It is likely that the seasonal change from November to February (moderate season) could limit disease transmission due to a reduction in mosquito spread.

Most of Mauritania (77%) is considered arid or semi-arid, and the movement of animals in search of water and pastures increases the risk of spreading the disease. Uncontrolled cross-border pastoral movements also increase the risk of spreading regional disease to Senegal, Mali and Morocco, and cooperation between neighboring countries is crucial for the surveillance, prevention and control of RVF.

People who have direct or indirect contact with infected animals or with the blood or organs of infected animals in endemic regions of RVF have a higher risk of infection. This may include livestock farmers, farmers, slaughterhouse workers, veterinarians and others who work with animals and related products.

To date, human-to-human transmission of RVF has not been documented.

The level of risk at the national level is considered high: this epidemic poses a high risk to human health with a death rate of 33% (25/75) as of 31 October 2020. Confirmation of virus circulation in animals from several attacks poses a high risk of human infection. This epidemic shows a large geographical phenomenon and moves through the movement of animals in agropastoral zones at the national level.

As of November 7, 2020, 11 of the 15 regions affected by the epidemic. The national human oversight system faces operational challenges, from early detection to case notification. Support measures are insufficient. High mortality would be associated with late referral of patients with severe symptoms, admitted to health facilities with limited medical care.

The overall risk at regional level is moderate: There is a real risk of regional spread due to favorable vector spread conditions (heavy rains, vector spread, floods, lack of sanitation), animal density and uncontrolled movement of livestock between regions and border countries (Mali , Senegal, Morocco).

WHO advice

Rift Valley Fever is an ecological zoonosis transmitted by mosquitoes and that primarily affects domestic animals (including cattle, sheep, camels and goats). Human cases often occur near livestock outbreaks in an environment conducive to the transmission of mosquito vectors locally. Most human infections are the result of direct or indirect contact with the blood or organs of infected animals. Care must be taken when handling sick animals or human patients, their products and laboratory samples. Raising awareness of risk factors for RVF infection, as well as other protective measures such as vector control and protection against mosquito bites, are key to reducing human infections and deaths. Public health messages to reduce risk should focus on:

• Reducing the risk of human-to-human transmission as a result of insecure animal husbandry and slaughter. Exercising hand hygiene, wearing gloves and other appropriate individual protective equipment when handling sick animals or their tissues or when slaughtering animals
• Reducing the risk of human-to-human transmission resulting from unsafe consumption of fresh blood, raw milk or animal tissue by thorough cooking before meals
• Reducing the risk of mosquito bites by carrying out vector control activities (eg spraying with insecticides and using larvicides to reduce mosquito breeding sites), using insect nets impregnated with mosquitoes and repellents, covering clothing
• Avoiding outdoor activities at the peak of vector species bite time

Because the outbreak of RVF in animals precedes human cases, the establishment of an active animal health surveillance system is crucial to provide early warning to animal authorities and public health. Routine immunization of animals in endemic areas can prevent RVF epizootics. Vaccination campaigns are not recommended during outbreaks, as this may increase transmission among the herd by the needle spread of the virus. Therefore, public education, livestock quarantine and slaughter bans may be the most effective measures against the spread of the disease in the pre- and outbreak stages.

The WHO advises against the application of any travel or trade restrictions in Mauritania or the affected area based on current data available on this event.

For more information on Rift Valley fever, see the links below: