Rift Valley Fever – Mauritania

The Ministry of Health (MoH) notified WHO that between 13 September and 1 October 2020, eight cases of Rift Valley Fever (RVF) including seven deaths were confirmed in animal breeders. Districts affected 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 for Public Health Research (INRSP) in Nouakchott. The age of infected patients varied between 16 and 70 years old and included one woman and seven men. All seven deaths occurred among hospitalised patients with fever and haemorrhagic syndrome (petechia, gingivorrhagia) and vomiting.

Between 4 September to 7 November 2020, a total of 214 people were sampled and their samples have been sent to the INRSP for laboratory testing with a total of 75 testing positive for RVF (RT-PCR and serology by enzyme-linked immunosorbent assay (ELISA). Positive cases have been reported in 11 of 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 Tagant region is the most affected (38/75, 51%) with principal hotspot districts being Tidjikja and Moudjeria. Thus far a total of 25 deaths have been reported from this outbreak.

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

Public Health Response

Since the beginning of the outbreak, WHO has been working closely with the Ministry of Health to respond to the current outbreak and monitor the evolution of the epidemiological situation.

WHO is supporting the following public health activities being implemented to respond to the outbreak:

  • Regular coordination and technical meetings between public health and animal health sectors
  • Coordination of the outbreak response activities at the human-animal interface in all affected regions
  • Epidemiological investigation
  • Reinforcement of diagnostic capacities
  • Preparation of communication tools
  • Mobilization of resources and expertise

Joint field missions by FAO, OIE and WHO experts are planned to support MOH and the Ministry of Rural Development in the prevention and control of RVF outbreaks, in particular with regards to laboratory capacities, surveillance and risk communication to various populations at risk, and in other aspects related to the “One Health” concept.

WHO risk assessment

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

RVF outbreaks have been reported previously in Mauritania, and the country has experienced six major outbreaks in the past (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 outbreak affecting human and animals occurred after heavy, unusual and prolonged rainfall in the regions with high animal density which contributed to the proliferation of vectors and the spread of the virus. During hot seasons, people spend more time in rural areas with history of RVF transmission, resting at night in the open air. This could be a risk factor for exposure to mosquitoes and others vector of the disease. It is likely that the season change from November to February (temperate season) could limit the transmission of the disease with the due the reduction of the proliferation of mosquitoes.

The majority of Mauritania (77%) is considered arid or semi-arid and the movement of animals in search of water and pasture increases the risk of disease spread. Uncontrolled cross-border pastoral movements also increases the risk for regional disease spread to Senegal, Mali and Morocco, and cooperation between neighbouring countries is essential for RVF surveillance, prevention and control.

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

To date, no human-to-human transmission of RVF has been documented.

The level of risk at national level is considered high: this epidemic represents a high risk for human health with a proportion of deaths of 33% (25/75) as of 31 October 2020. Confirmation of the circulation of the virus in animals from several outbreaks poses a great risk of human infection. This epidemic shows a large geographic emergence and is moving through animal movements in agro-pastoral zones at the national level.

As of 7 November October 2020, 11 of 15 regions affected by the epidemic. The national human surveillance system faces operational challenges ranging from early detection to notification of cases. Support measures are insufficient. The high lethality would be linked to the late referral of patients with severe symptoms, admitted to care structures with limited medical care.

The overall risk at the regional level is moderate: There is a real risk of propagation at the regional level given the favorable conditions of propagation of the vectors (heavy rainfall, proliferation of vectors, floods, lack of sanitation), animal density, and uncontrolled movements of livestock between regions and border countries (Mali, Senegal, Morocco).

WHO advice

Rift Valley Fever is an environmentally-driven mosquito-borne zoonosis that primarily affects domestic animals (including cattle, sheep, camels and goats). Human cases often occur in proximity to outbreaks in livestock in an environment favourable for mosquito vectors to transmit the virus locally. Most human infections result from 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 the risk factors of RVF infection as well as other protective measures such as vector control and protection against mosquito bites is the key to reduce human infection and deaths. Public health messages for risk reduction should focus on:

  • Reducing the risk of animal-to-human transmission as a result of unsafe animal husbandry and slaughtering practices. Practicing 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 animal-to-human transmission arising from the unsafe consumption of fresh blood, raw milk or animal tissue by thoroughly cooking before eating
  • Reducing the risk of mosquito bites through the implementation of vector control activities (e.g. insecticide spraying and use of larvicide to reduce mosquito breeding sites), use of insecticide-impregnated mosquito nets and repellents, covering clothing
  • Avoiding outdoor activity at peak biting times of the vector species

As outbreaks of RVF in animals precede human cases, the establishment of an active animal health surveillance system is essential in providing early warning for animal and public health authorities. Routine animal immunization in endemic areas can prevent RVF epizootics. Vaccination campaigns are not recommended during an outbreak as it may intensify transmission among the herd through needle propagation of the virus. Therefore, public education, livestock quarantine, and slaughter bans are perhaps the most effective measures against disease spread during the pre-outbreak and outbreak phases

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

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