Seroprevalence and Risk Factors of Crimean-Congo Hemorrhagic Fever in Cattle of Smallholder Farmers in Central Malawi

Abstract

Crimean-Congo hemorrhagic fever virus (CCHFV) is endemic in Africa, Asia, and Eastern Europe where it circulates among animals and ticks causing sporadic outbreaks in humans. Although CCHF is endemic in sub-Saharan Africa, epidemiological information is lacking in many countries, including Malawi. To assess the risk of CCHF in Malawi, we conducted an epidemiological study in cattle reared by smallholder livestock farmers in central Malawi. A cross-sectional study was conducted in April 2020 involving seven districts, four from Kasungu and three from Lilongwe Agriculture Development Divisions. A structured questionnaire was administered to farmers to obtain demographic, animal management, and ecological risk factors data. Sera were collected from randomly selected cattle and screened for CCHF virus (CCHFV) specific antibodies using a commercial ELISA kit. Ticks were collected from cattle and classified morphologically to species level. An overall CCHFV seropositivity rate of 46.9% (n = 416; 95% CI: 42.0–51.8%) was observed. The seropositivity was significantly associated with the age of cattle (p < 0.001), sex (p < 0.001), presence of ticks in herds (p = 0.01), district (p = 0.025), and type of grazing lands (p = 0.013). Five species of ticks were identified, including Hyalomma truncatum, a known vector of CCHFV. Ticks of the species Hyalomma truncatum were not detected in two districts with the highest seroprevalence for CCHF and vector competency must be further explored in the study area. To our knowledge, this is the first report of serologic evidence of the presence of CCHV among smallholder cattle in central Malawi. This study emphasizes the need for continued monitoring of CCHFV infection among livestock, ticks, and humans for the development of data-based risk mitigation strategies.

Systematic Review on Crimean–Congo Hemorrhagic Fever Enzootic Cycle and Factors Favoring Virus Transmission: Special Focus on France, an Apparently Free-Disease Area in Europe

“…This phenomenon was reported in cattle from Pakistan (88) and was considered a reliable preventive strategy when animals from Sudan were introduced into Saudi Arabia (104). This was clearly linked to the tick burden of animals, which was also measured in some studies (33,35,(87)(88)(89)(90)(91). Conversely, some studies reported insignificant or opposite effects of acaricide treatments or tick control actions but a little information was provided on the chemicals and methods used to assess their reliability (35,87,89).…”

“…Several studies conducted in Africa and Asia have shown that CCHF seroprevalence significantly increases with the animal age, either in cattle, small ruminants, and camels (33,35,(87)(88)(89)(90)(91)(92)(93)(94)(95)(96)(97). This correlation was mainly attributed to an increasing probability of an animal to be exposed to infected tick vectors, contract CCHFV, and develop an immune response in relation with increasing age (33). Such an additive effect of age seems obvious as antibodies are assumed to persist for a long period in animals, up to several years (98).…”

“…Apart from the breed, sex as another host-related risk factor was also tested in several studies and its effect was mostly insignificant on the CCHFV seroprevalence (88,91,96,97). The only exception was for cattle from Malawi and South Africa where CCHFV seroprevalence was higher in females than males, although this cannot be attributed to intrinsic resistance in females against ticks (33,87). In these countries, female cattle are raised mainly for breeding purposes, meaning they spend more time in the fields grazing and therefore have an increased risk of tick exposure.…”

“…In the end, a total of 1,035 resources, dating from 1947 to 2021, were selected for data extraction and were sorted based on their titles, abstracts, and keywords into a few categories ( Figure 1 ). For the purpose of our review, we directly removed those related to CCHFV virology number = 226, CCHF diagnosis and detection methods ( 32 ), CCHF symptoms in the form of case reports number = 134, as well as CCHF control and treatment ( 33 ) as they were not useful for the data extraction. As we focused on the enzootic circulation of CCHFV, we also removed the articles studying introduction pathways ( 15 ).…”

“…In these countries, female cattle are raised mainly for breeding purposes, meaning they spend more time in the fields grazing and therefore have an increased risk of tick exposure. Males, however, are used for drought power and stay away from pastures longer than females and young cattle, particularly during the rainy season when crop cultivation is at its peak and ticks are active ( 33 ). In two studies conducted on cattle from Sudan, animal body condition was also tested in relation to CCHFV seroprevalence but its effect was insignificant to the assumption that poor body conditions may invoke higher susceptibility of CCHFV infection in animals ( 35 , 89 ).…”