Endemic persistence of a highly contagious pathogen: Foot-and-mouth disease in its wildlife host

Abstract

Persistence of acute viruses How do highly contagious viruses that cause acute infections hang on to cause recurrent problems in a population? It should be expected that such infections would fade out as herd immunity develops, but foot and mouth disease virus (FMDV) can reemerge. Jolles et al . explored how FMDV remains endemic in African buffalo and serves as a reservoir for disease in domestic livestock (see the Perspective by Hampson and Haydon). The authors found that the virus persists in the population in carrier animals. Inconspicuous, rare, and sporadic transmission rescues the virus from fade-out, assisted by antigenic shift and the seasonal birth of susceptible calves. —CA

Viral dynamics and immune responses to foot-and-mouth disease virus in African buffalo (Syncerus caffer)

“…We could not find any association of the carrier state with the route of infection or acute host responses, as suggested for cattle [ 20 ]. We and others have demonstrated that buffalo can remain persistently infected with FMDV for months and years [ 5 , 25 , 49 ] and although transmission from carrier buffalo to naïve is difficult to reproduce [ 44 , 50 ], a recent publication demonstrated that it is indeed the inclusion of occasional transmission from carriers that rescues FMDV from extinction in isolated African buffalo populations [ 10 ].…”

“…FMDV is mainly transmitted directly from infected animals in close contact with naïve animals during acute infection. FMDV has a very high rate of transmission and R 0 values during early stages of the disease were considered to be 21–88 for cattle, 1–14 for sheep [ 7 – 9 ] and very recently, the R 0 estimated for African buffalo was 5–15.8 [ 10 ]. In cattle, the onset of clinical signs occurs 3–4 days after infection and transmission occurs, on average, 0.5 days after the appearance of clinical signs [ 11 ] when very high titres of virus are found in the damaged epithelium due to vesicle formation and vesicular fluid [ 12 ].…”

Foot-and-mouth disease virus localisation on follicular dendritic cells and sustained induction of neutralising antibodies is dependent on binding to complement receptors (CR2/CR1)

“…A carrier of FMDV is defined as an animal from which live virus can be recovered from the nasopharynx after 28 days following infection, which frequently occurs in ruminants after acute infection [ 3 ]. Only ruminants have been shown to become FMDV carriers, and among them, the majority of infected African buffalo become carriers after acute infection and can carry FMDV for up to 5 years or more, which is why African buffalo are considered the primary reservoir of FMDV in Africa [ 4 – 7 ]. Over 50% of cattle exposed to FMDV become carriers [ 4 , 5 , 8 ], and although current vaccines prevent clinical disease, they do not prevent primary infection in the nasopharynx, therefore vaccinated animals can still become carriers of FMDV [ 9 ].…”

Viral Population Diversity during Co-Infection of Foot-And-Mouth Disease Virus Serotypes SAT1 and SAT2 in African Buffalo in Kenya

“…The mechanisms of FMDV persistence within the buffalo population has been an important area of investigation because most studies fail to observe transmission from persistently infected animals. A recent study combining experimental infection and modeling concluded that this persistence cannot be sustained only by infections in young calves after waning of maternal immunity, and that virus transmission from persistently infected carrier animals is needed for maintenance of the virus in the population [ 43 ]. Animals persistently infected with multiple FMDV genotypes may play an important role in virus evolution and divergence, and in the antigenic differences, allowing for infection or transmission to a new host.…”