Heterogeneity in a communal cattle-farming system in a zone endemic for foot and mouth disease in South Africa

In South Africa, communal livestock farming is predominant in the foot and mouth disease control zone adjacent to the Greater Kruger National Park (KNP), where infected African buffaloes are common. During routine veterinary inspections of cattle in this area, a large amount of production and demographic parameters were being recorded. These data were collated for a five-year period (2003-2007) in three study sites to better understand the temporal dynamics and spatial heterogeneity in this system. A decreasing gradient from South to North with respect to both human and cattle population densities was observed. Rainfall and human population density alone could explain 71% of the variation in cattle density. Northern and central sites showed an overall decrease in total cattle numbers (15.1 and 2.9%, respectively), whereas a 28.6% increase was recorded in the South. The number of cattle owners in relation to cattle numbers remained stable during the study period. Only 4.0% of households in the South own cattle, compared to 13.7 and 12.7% in the North and Centre. The overall annual calving rate was 23.8%. Annual mortality rates ranged from 2.4 to 3.2%. Low calf mortality (2.1%) was recorded in the North compared to the South (11.6%). Annual off-take in the form of slaughter averaged 0.2, 11.7, and 11.0% in the North, Central and South sites, respectively. These figures provide valuable baseline data and demonstrate considerable spatial heterogeneity in cattle demography and production at this wildlife-livestock interface, which should be taken into consideration when performing disease risk assessments or designing disease control systems.

Taenia solium Infections in a rural area of Eastern Zambia-a community based study

Background

Taenia solium taeniosis/cysticercosis is a parasitic infection occurring in many developing countries. Data on the status of human infections in Zambia is largely lacking. We conducted a community-based study in Eastern Zambia to determine the prevalence of human taeniosis and cysticercosis in a rural community.

Methods and Findings

Stool and serum samples were collected from willing participants. Geographical references of the participants' households were determined and household questionnaires administered. Taeniosis was diagnosed in stool samples by coprology and by the polyclonal antibody-based copro-antigen enzyme-linked immunosorbent assay (copro-Ag ELISA), while cysticercosis was diagnosed in serum by the B158/B60 monoclonal antibody-based antigen ELISA (sero-Ag ELISA). Identification of the collected tapeworm after niclosamide treatment and purgation was done using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP). A total of 255 households from 20 villages participated in the study, 718 stool and 708 serum samples were collected and examined. Forty-five faecal samples (6.3%) were found positive for taeniosis on copro-Ag ELISA while circulating cysticercus antigen was detected in 5.8% (41/708) individuals. The tapeworm recovered from one of the cases was confirmed to be T. solium on PCR-RFLP. Seropositivity (cysticercosis) was significantly positively related to age (p = 0.00) and to copro-Ag positivity (taeniosis) (p = 0.03) but not to gender. Change point analysis revealed that the frequency of cysticercus antigens increased significantly in individuals above the age of 30. Copro-Ag positivity was not related to age or gender. The following risk factors were noted to be present in the study community: free-range pig husbandry system and poor sanitation with 47.8% of the households visited lacking latrines.

Conclusions

This study has recorded high taeniosis and cysticercosis prevalences and identified the need for further studies on transmission dynamics and impact of the disease on the local people.

Taenia solium taeniosis/cysticercosis is a zoonotic infection endemic in many developing countries, with humans as the definitive host (taeniosis) and pigs and humans as the intermediate hosts (cysticercosis). When humans act as the intermediate host, the result can be neurocysticercosis, which is associated with acquired epilepsy, considerable morbidity and even mortality. In Africa, most studies have been carried out in pigs with little or no data in humans available. In this human study, conducted in a rural community in Eastern Zambia, prevalences for taeniosis and cysticercosis were determined at 6.3% and 5.8% respectively, indicating the hyperendemicity of the area. Cysticercosis infection was strongly related with age, with a significant increase in prevalence occurring in individuals from the age of 30 onward. A collected tapeworm was confirmed to be T. solium. Risk factors associated with the transmission and maintenance of the parasite such as free roaming pigs, households without latrines, backyard slaughter of pigs without inspection and consumption of undercooked pork were also present. The findings of this work have identified the need for further research in the transmission dynamics and the burden that this infection has on the resources of poor local people.

Vector competence of Glossina austeni and Glossina brevipalpis for Trypanosoma congolense in KwaZulu-Natal, South Africa

Tsetse-transmitted trypanosomosis (nagana) has been the cause of stock losses in the recent past and still presents a major problem to livestock owners in certain areas of KwaZulu- Natal, South Africa. Over 10 000 cattle mortalities were reported in the 1990 nagana outbreak. Although information on the distribution and abundance of the tsetse flies Glossina brevipalpis and Glossina austeni in KwaZulu-Natal exists, data on their vector competence are lacking. This study aimed to determine the rate of natural Trypanosoma congolense infection by field-collected as well as colony-reared flies of these species. A total of 442 field-collected G. brevipalpis and 40 G. austeni flies were dissected immediately after collection to determine their infection rates, whilst 699 G. brevipalpis and 49 G. austeni flies were fed on susceptible animals in 10 and four batches, respectively, for use in xenodiagnosis experiments. Teneral colony flies were fed on infected animals and dissected 21 days post infection to confirm their infectivity testing. Glossina austeni harboured 8% immature and mature infections. In G. brevipalpis, the infection with the immature stages was lower (1%) and no mature infections were observed. Although all four batches of G. austeni transmitted T. congolense to four susceptible animals, no transmission resulted from 10 batches of G. brevipalpis fed on susceptible cattle. Colony-derived G. austeni (534) and G. brevipalpis (882) were fed on four bovines infected with different T. congolense isolates. Both G. austeni and G. brevipalpis acquired trypanosome infection from the bovines, with immature infection ranges of 20% - 33% and 1% - 4%, respectively. Parasites, however, only matured in G. austeni (average = 4%). Glossina austeni plays a larger role in the epidemiology of animal trypanosomosis in KwaZulu-Natal than G. brevipalpis and therefore more focus should be aimed at the former when control measures are implemented.

High prevalence of drug resistance in animal trypanosomes without a history of drug exposure

Background

Trypanosomosis caused by Trypanosoma congolense is a major constraint to animal health in sub-Saharan Africa. Unfortunately, the treatment of the disease is impaired by the spread of drug resistance. Resistance to diminazene aceturate (DA) in T. congolense is linked to a mutation modifying the functioning of a P2-type purine-transporter responsible for the uptake of the drug. Our objective was to verify if the mutation was linked or not to drug pressure.

Methodology/Principal Findings

Thirty-four T. congolense isolates sampled from tsetse or wildlife were screened for the DA-resistance linked mutation using DpnII-PCR-RFLP. The results showed 1 sensitive, 12 resistant and 21 mixed DpnII-PCR-RFLP profiles. This suggests that the mutation is present on at least one allele of each of the 33 isolates. For twelve of the isolates, a standard screening method in mice was used by (i) microscopic examination, (ii) trypanosome-specific 18S-PCR after 2 months of observation and (iii) weekly trypanosome-specific 18S-PCR for 8 weeks. The results showed that all mice remained microscopically trypanosome-positive after treatment with 5 mg/kg DA. With 10 and 20 mg/kg, 8.3% (n = 72) and 0% (n = 72) of the mice became parasitologically positive after treatment. However, in these latter groups the trypanosome-specific 18S-PCR indicated a higher degree of trypanosome-positivity, i.e., with a unique test, 51.4% (n = 72) and 38.9% (n = 72) and with the weekly tests 79.2% (n = 24) and 66.7% (n = 24) for 10 and 20 mg/kg respectively.

Conclusion/Significance

The widespread presence of the DA-resistance linked mutation in T. congolense isolated from wildlife suggests that this mutation is favourable to parasite survival and/or its dissemination in the host population independent from the presence of drug. After treatment with DA, those T. congolense isolates cause persisting low parasitaemias even after complete elimination of the drug and with little impact on the host's health.

Trypanosomosis is responsible for the death of 3 million heads of cattle yearly, with 50 million animals at risk in sub-Saharan Africa. DA, a commonly used drug against the disease, was marketed decades ago. Drug resistance is reported in 21 African countries. A common argument about the origin of drug resistance is the selection by the drug of rare individuals that are naturally resistant and the propagation of those individuals in the population because of the competitive advantage they have when exposed to drug. When the drug pressure decreases, the wild-type individuals regain their supremacy. The principal objective of this study was thus to estimate the prevalence of trypanosomes resistant to DA in a population that was never exposed to the drug. Our results showing a high prevalence of drug resistance in environments free of any drug pressure is thought provoking and suggests that ceasing the use of DA will not allow for a return to a DA-sensitive population of trypanosomes. Drug resistance in animal trypanosomes thus present a pattern different from what is observed with Plasmodium sp. (causative agent of malaria) where a complete stoppage in the use of the chloroquine allows for a return to drug sensitivity.

Methodology for assessing determinants of manure use in urban areas of Africa

The objectives of this study were to identify the major determinants (e.g. zootechnical and socio-economic parameters) of manure management practised by urban livestock keepers. Data were collected from four single-visit, multi-object surveys in three cities of Africa. The livestock keepers were classified either as 'good user' or 'bad user' of manure depending on how they use the manure. The results of this study indicate that the habit of manure utilization shows geographical differences. In general, livestock keepers engaged in agricultural activities are good manure users. Furthermore, manual workers, traders or the self-employed are better manure users than other professional groups. The manure utilization varies also in function of the livestock numbers. In Brazzaville, the habit of selling animals influenced manure management positively. Experience of keeping livestock before the civil war in Brazzaville was also a determining factor of manure use in the post-war urban livestock keeping in 2001. When designing policies to reduce the environmental effects of urban livestock keeping, the highlighted factors can assist city planners to understand how urban livestock keepers use manure. Using the non-parametric classification tree method CART, two approaches were used to select an optimal classification of 'bad' manure users: the 'Cook and Goldman rule' and the 'Classification with different misclassification cost ratios' method. The optimal tree was selected by using receiver operating characteristics curve information. This method can be useful in assessing other aspects of waste management.

Distribution and density of tsetse flies (Glossinidae: Diptera) at the game/people/livestock interface of the Nkhotakota Game Reserve human sleeping sickness focus in Malawi

In large parts sub-Saharan Africa, tsetse flies, the vectors of African human or animal trypanosomiasis, are, or will in the foreseeable future, be confined to protected areas such as game or national parks. Challenge of people and livestock is likely to occur at the game/livestock/people interface of such infested areas. Since tsetse control in protected areas is difficult, management of trypanosomiasis in people and/or livestock requires a good understanding of tsetse population dynamics along such interfaces. The Nkhotakota Game Reserve, an important focus of human trypanosomiasis in Malawi, is a tsetse-infested protected area surrounded by a virtually tsetse-free zone. The abundance of tsetse (Glossina morsitans morsitans) along the interface, within and outside the game reserve, was monitored over 15 months using epsilon traps. A land cover map described the vegetation surrounding the traps. Few flies were captured outside the reserve. Inside, the abundance of tsetse at the interface was low but increased away from the boundary. This uneven distribution of tsetse inside the reserve is attributed to the uneven distribution of wildlife, the main host of tsetse, being concentrated deeper inside the reserve. Challenge of people and livestock at the interface is thus expected to be low, and cases of trypanosomiasis are likely due to people and/or livestock entering the reserve. Effective control of trypanosomiasis in people and livestock could be achieved by increasing the awareness among people of dangers associated with entering the reserve.

Five-fold increase in Trypanosoma congolense isolates resistant to diminazene aceturate over a seven-year period in Eastern Zambia

Two groups of Trypanosoma congolense isolates collected from cattle in 1996 (n=39) and 2003 (n=38) in the Eastern Province of Zambia were analyzed by BclI-PCR-RFLP to assess the evolution of diminazene aceturate (DA) resistance over a period of seven years. The results show a significant increase of DA resistance in this relatively short period of time. In 1996, among the 39 isolates, 61.5% were found sensitive, 12.8% resistant and 25.7% had a mixed BclI-PCR-RFLP profile. In 2004, among the 38 isolates, 10.5% were found sensitive, 63.2% were resistant and 26.3% showed a mixed BclI-PCR-RFLP profile. In vivo tests in mice showed that isolates with a sensitive or mixed RFLP profile were sensitive to DA whereas isolates with a resistant RFLP profile were resistant. Since there are no indications that the drug pressure has increased between 1996 and 2003, it is suggested that genetic exchange of resistance genes might explain the increased frequency of resistance to DA.

Energy metabolism of bloodstream form Trypanosoma theileri

Bloodstream form Trypanosoma theileri degrades glucose to acetate (47%) and succinate (45%) and, therefore, does not solely rely on glycolysis for ATP production. This trypanosomatid does not use amino acids for energy metabolism. These results refute the prevailing hypothesis that substrate availability determines the type of energy metabolism of trypanosomatids.